Immune correlates analysis of the PREVENT-19 COVID-19 vaccine efficacy clinical trial

Immunogenicity and safety of SARS-CoV-2 recombinant protein vaccine (CHO cell) LYB001 as a heterologous booster following two- or three-dose inactivated COVID-19 vaccine in adults aged ≥18 years: interim results of a randomized, active-controlled, double-blinded, phase 3 trial

BACKGROUND

LYB001 is a recombinant protein COVID-19 vaccine displaying a receptor-binding domain (RBD) in a highly immunogenic array on virus-like particles (VLPs). This study assessed the immunogenicity and safety of LYB001 as a booster.

RESEARCH DESIGN AND METHODS

In this randomized, active-controlled, double-blinded, phase 3 trial, participants aged ≥ 18 years received a booster with LYB001 or ZF2001 (Recombinant COVID-19 Vaccine). The primary endpoint was to compare the geometric mean titer (GMT) of neutralizing antibodies against Omicron BA.4/5 at 14 days after the booster.

RESULTS

Overall, 1,200 participants aged ≥ 18 years were enrolled, 599 received LYB001, and 601 received ZF2001. Based on similar baseline level, the 14-day GMT ratio (LYB001/ZF2001) against Omicron BA.4/5 was 1.39 (95% CI: 1.25, 1.56), demonstrating superiority (95% CI lower limit > 1) of LYB001. The spike protein-binding IgG concentrations induced by LYB001 were significantly higher than those induced by ZF2001 on day 14 and day 28 after the booster (p-value <0.0001). LYB001 recipients reported more adverse reactions than ZF2001 recipients (21.4% vs. 15.0%); however, all adverse reactions in the LYB001 group were mild-to-moderate.

CONCLUSIONS

LYB001 is highly immunogenic and retains a well-characterized safety profile in adults aged ≥ 18 years.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov, identifier is NCT05664932.

Immunogenicity and Safety of Influenza and COVID-19 Multicomponent Vaccine in Adults ≥50 Years: A Randomized Clinical Trial

Importance

Uptake of recommended seasonal influenza and COVID-19 vaccines remains suboptimal.

Objective

To assess the immunogenicity and safety of an investigational mRNA-1083 vaccine against seasonal influenza and SARS-CoV-2 in adults 50 years and older.

Design, Setting, and Participants

This phase 3, randomized, observer-blinded trial was conducted across 146 US sites in adults 50 years and older enrolled between October 19, 2023, and November 21, 2023. Data extraction was complete on April 9, 2024.

Interventions

Participants in 2 age cohorts (≥65 years and 50-64 years) were randomly assigned (1:1) to receive mRNA-1083 plus placebo or coadministered licensed quadrivalent seasonal influenza (≥65 years: high-dose quadrivalent inactivated influenza vaccine [HD-IIV4]; 50-64 years: standard-dose IIV4 [SD-IIV4]) and COVID-19 (all ages: mRNA-1273) vaccines.

Main Outcomes and Measures

The primary objectives were to demonstrate the noninferiority of humoral immune responses following mRNA-1083 vs comparators against vaccine-matched strains at day 29 and to evaluate the reactogenicity and safety of mRNA-1083. Secondary objectives included demonstration of superiority of humoral immune responses elicited by mRNA-1083 relative to comparators at day 29.

Results

Overall, 8015 participants were enrolled and vaccinated (4017 aged ≥65 y and 3998 aged 50-64 y). Among adults 65 years and older and 50 to 64 years, the median age was 70 and 58 years, 54.2% and 58.8% were female, 18.4% and 26.7% were Black or African American, and 13.9% and 19.3% were Hispanic or Latino, respectively. Noninferior immunogenicity of mRNA-1083 was demonstrated against all vaccine-matched influenza and SARS-CoV-2 strains based on lower bound of the 97.5% CI of the geometric mean ratio greater than 0.667 and lower bound of the 97.5% CI of the seroconversion/seroresponse rate difference greater than -10%. mRNA-1083 elicited higher immune responses than SD-IIV4 (50-64 years) for all 4 influenza strains and HD-IIV4 (≥65 years) for 3 influenza strains (A/H1N1, A/H3N2, B/Victoria) and against SARS-CoV-2 (all ages). Solicited adverse reactions were numerically higher in frequency and severity after mRNA-1083 vaccination than comparators in both age cohorts (≥65 y: 83.5% and 78.1%; 50-64 y: 85.2% and 81.8%); most were grade 1 or 2 in severity and of short duration. No safety concerns were identified.

Conclusions and Relevance

In this study, mRNA-1083 met noninferiority criteria and induced higher immune responses than recommended standard care influenza (standard and high dose) and COVID-19 vaccines against all 4 influenza strains (among those ages 50-64 y), the 3 clinically relevant influenza strains (among those aged ≥65 y), and SARS-CoV-2 (all ages), with an acceptable tolerability and safety profile.

Trial Registration

ClinicalTrials.gov Identifier: NCT06097273.

Immunogenicity and safety of a monovalent omicron XBB.1.5 SARS-CoV-2 recombinant spike protein vaccine as a heterologous booster dose in US adults: interim analysis of a single-arm phase 2/3 study

BACKGROUND

Authorities globally recommended a monovalent omicron XBB.1.5-based COVID-19 vaccine for the 2023-24 season. The Novavax COVID-19 vaccine, NVX-CoV2601, contains XBB.1.5 recombinant spike protein, based on an authorised prototype vaccine (NVX-CoV2373) technology. We aimed to determine whether a single dose of NVX-CoV2601 versus NVX-CoV2373 (from a previous study [2019nCoV-311 part 2]) produced superior neutralising antibody (nAb) responses, and non-inferior seroresponse rates to XBB.1.5, after three or more previous mRNA-based COVID-19 vaccinations.

METHODS

In part 1 of this single-arm, phase 2/3 study (2019nCoV-313), participants aged 18 years or older who had been previously vaccinated with three or more doses of mRNA-1273 (Moderna) or BNT162b2 (Pfizer-BioNTech) were enrolled across 30 US centres (research groups and universities) located across 20 states. Participants received one intramuscular injection of NVX-CoV2601 (5 μg XBB.1.5 spike plus 50 μg Matrix-M adjuvant). Coprimary endpoints were superiority of baseline-adjusted nAb geometric mean XBB.1.5 titres (adjusted GMTs), with superiority declared when the lower bound of the 95% CI for the GMT ratio (GMTR) was greater than 1, and non-inferiority of seroresponse rates, with non-inferiority declared when the lower bound of the 95% CI for the seroresponse rate difference was greater than -10%, on day 28; comparisons were made for NVX-CoV2601 administered in this study versus NVX-CoV2373 administered in part 2 (group G) of the 2019nCoV-311 study. Coprimary endpoints were assessed in the per-protocol immunogenicity set (ie, all participants who received study vaccine, underwent 28 days of follow-up, had day 0 and day 28 samples available, and had no major protocol deviations). Safety was a secondary endpoint and included assessments of solicited treatment-emergent adverse events up to 7 days and unsolicited treatment-emergent adverse events up to 28 days after vaccination in the safety analysis set (ie, all participants who received study vaccine). Here we report the prespecified interim analysis of immunogenicity and safety up to day 28. This study is registered with ClinicalTrials.gov, NCT05975060, and is now complete.

FINDINGS

Between Sept 7 and Sept 8, 2023, 380 individuals were screened, of whom 332 were enrolled and received study vaccine. At the 28-day interim analysis database lock (Jan 17, 2023), the per-protocol analysis sets included 309 (93%) of 332 NVX-CoV2601 recipients and 227 (90%) of 252 NVX-CoV2373 recipients. Mean age of NVX-CoV2601 recipients was 52·1 years (SD 16·1); 192 (62%) of 309 were female and 117 (38%) were male. Mean age of NVX-CoV2373 recipients was 42·2 years (13·4); 128 (56%) of 227 were female and 99 (44%) were male. At day 28, the baseline-adjusted nAb GMT for NVX-CoV2601 was 905·9 (95% CI 807·1-1016·8) and for NVX-CoV2373 was 156·6 (137·0-179·0); the between-group adjusted GMTR was 5·8 (95% CI 4·9-6·9). In the per-protocol immunogenicity set, seroresponse rates were 64% (196 of 305) among recipients of NVX-CoV2601 and 7% (16 of 227) among recipients of NVX-CoV2373, with a seroresponse rate difference of 57% (95% CI 51-63). In the NVX-CoV2601 group, within 7 days, solicited local treatment-emergent adverse events were reported in 189 (57%) of 332 participants (including one [<1%] grade 3 or worse event; tenderness) and solicited systemic treatment-emergent adverse events were reported in 158 (48%) participants (including four [1%] participants with one or more grade 3 events; malaise [n=3], headache [n=2], fatigue [n=1], and muscle pain [n=1]). The most common solicited treatment-emergent adverse events were tenderness (171 [52%]) and pain (98 [30%]) at the injection site, fatigue (97 [29%]), and muscle pain (97 [29%]). Up to day 28, unsolicited adverse events considered related to study vaccination in the NVX-CoV2601 group occurred in five (2%) participants (one for each of asthma, axillary pain, diarrhoea, hypertension [which was medically attended], and presyncope). No serious adverse events due to study product, adverse events of special interest, or deaths due to study product occurred, and no study discontinuations due to treatment-emergent adverse events occurred.

INTERPRETATION

The coprimary endpoints were met, and NVX-CoV2601 was well tolerated. These interim data support NVX-CoV2601 use per guidance for XBB.1.5-directed COVID-19 vaccines and demonstrate the adaptability of this vaccine platform for updated SARS-CoV-2 spike proteins.

FUNDING

Novavax.

A systems biology approach to define SARS-CoV-2 correlates of protection

Correlates of protection (CoPs) for SARS-CoV-2 have yet to be sufficiently defined. This study uses the machine learning platform, SIMON, to accurately predict the immunological parameters that reduced clinical pathology or viral load following SARS-CoV-2 challenge in a cohort of 90 non-human primates. We found that anti-SARS-CoV-2 spike antibody and neutralising antibody titres were the best predictors of clinical protection and low viral load in the lung. Since antibodies to SARS-CoV-2 spike showed the greatest association with clinical protection and reduced viral load, we next used SIMON to investigate the immunological features that predict high antibody titres. It was found that a pre-immunisation response to seasonal beta-HCoVs and a high frequency of peripheral intermediate and non-classical monocytes predicted low SARS-CoV-2 spike IgG titres. In contrast, an elevated T cell response as measured by IFNγ ELISpot predicted high IgG titres. Additional predictors of clinical protection and low SARS-CoV-2 burden included a high abundance of peripheral T cells. In contrast, increased numbers of intermediate monocytes predicted clinical pathology and high viral burden in the throat. We also conclude that an immunisation strategy that minimises pathology post-challenge did not necessarily mediate viral control. This would be an important finding to take forward into the development of future vaccines aimed at limiting the transmission of SARS-CoV-2. These results contribute to SARS-CoV-2 CoP definition and shed light on the factors influencing the success of SARS-CoV-2 vaccination.

Antibody Responses and Infection Prevention Following the Sixth Vaccination Using the BA.1 Bivalent COVID-19 Vaccine Among Healthcare Workers During the XBB Variant Dominance in Japan

The effect of the antibodies elicited by bivalent mRNA vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (the original strain and Omicron variant BA.1) on preventing coronavirus disease 2019 (COVID-19) onset during the XBB variant dominance remains unknown. We conducted a prospective cohort study at Chiba University Hospital and examined healthcare workers who received the Pfizer-BioNTech bivalent mRNA COVID-19 vaccine (targeting the original and Omicron BA.1) as their sixth dose of COVID-19 vaccine. The serum antibodies against SARS-CoV-2 spike (S) protein were measured quantitatively. Participants who were not infected during the 60-day observation period following the sixth vaccination had significantly higher S antibody titers than those who were newly infected (27,756 U/mL, 95% confidence interval [CI] 24,988-30,831 U/mL vs. 15,321 U/mL, 95% CI 10,824-21,688 U/mL; P < 0.05). S antibody titer ≥15,500 U/mL decreased the risk of infection by 84%. Neutralizing antibody titers against the XBB.1.16 and XBB.1.42 variants were higher in age- and sex-matched non-infected individuals than in newly infected individuals during the post-vaccination observation period. S antibody titers were highly correlated with neutralizing antibody titers. In conclusion, after the sixth vaccination with a bivalent mRNA COVID-19 vaccine, high S antibody titers correlated with disease prevention, even in the presence of the XBB variants.

Variant-specific antibody correlates of protection against SARS-CoV-2 Omicron symptomatic and overall infections

Background

Vaccination and prior infection elicit neutralizing antibodies targeting SARS-CoV-2, yet the quantitative relationship between serum antibodies and infection risk against viral variants remains uncertain, particularly in underrepresented regions.

Methods

We investigated the protective correlation of pre-exposure serum neutralizing antibody levels, employing a panel of SARS-CoV-2 pseudoviruses (Omicron BA.1, Omicron BA.2, and ancestral D614G), and Spike-binding antibody levels, with symptomatic BA.1 or BA.2 SARS-CoV-2 infections and overall infection, in 345 household contacts from a SARS-CoV-2 household cohort study.

Results

A four-fold increase in homotypic-neutralizing (e.g., BA.1-neutralizing vs. BA.1 exposure) titers was correlated with protection from symptomatic infections (BA.1 protection: 28% [95%CI 12-42%]; BA.2 protection: 43% [20-62%]), and ancestral-neutralizing titers were also correlated with protection from either variant, but only at higher average levels than homotypic. Mediation analyses revealed that homotypic and D614G-neutralizing antibodies mediated protection from infection and symptomatic infection both from prior infection and vaccination.

Conclusions

These findings underscore the importance of monitoring variant-specific antibody responses and highlight that antibodies targeting circulating strains may be more predictive of protection from infection. Nevertheless, ancestral-strain-neutralizing antibodies remain relevant as a correlate of protection. Our study emphasizes the need for continued efforts to assess antibody correlates of protection.

Funding

We acknowledge funding from the U.S. N.I.H., the Open Philanthropy Project, and the Bill and Melinda Gates Foundation.

Research In Context

Evidence before this study

Based on searches of Google Scholar and PubMed, not restricted to English-language articles, using search terms including "correlates of protection," "SARS-CoV-2," "COVID-19," "BA.1," "BA.2," "neutralizing antibodies," "immune response," and "thresholds of protection" we identified multiple studies, primarily based on randomized clinical trials or prospective cohort designs, which have shown that serum SARS-CoV-2-neutralizing antibodies are informative correlates of protection from overall or symptomatic infection after vaccination or infection. Our search was limited to 2020 and later, and included several high-quality RCTs and cohort studies, as well as consideration of published meta-analyses. Often the serum correlates used were spike-binding or -neutralizing peak titers or baseline titers months before infection waves, and specific viral exposures for participants remained unknown. Most prior evidence related to neutralizing antibodies focused on neutralizing titers against the ancestral strain even when participants were challenged with later viral variants, although a small number of groups have also investigated neutralizing antibody titers directed against contemporaneous strains, such as Omicron BA.1. Furthermore, most studies of correlates of protection focused on vaccines widely available in North America and Europe; few serum antibody correlates of protection studies have included globally used COVID-19 vaccines, such as Soberana or Sputnik. Relatedly, Central America as a region has had no known studies of SARS-CoV-2 serum neutralizing antibody correlates of protection, to the best of our knowledge, despite the unique vaccine exposure histories of its residents and widespread infections before such vaccines became available.

Added value of this study

In this study, we used a household-based cohort study design with an embedded transmission study, in which we collected serum from household members just before they were exposed to a co-resident in the household who developed COVID-19. This design enabled correlates of protection analysis of serum antibody titers at the time of known exposure, relatively homogeneously across the cohort. Our study was conducted in Managua, Nicaragua, during Omicron BA.1 and BA.2 infection waves, presenting the first such study in Central America, and the first such study including participants who received some global vaccines. We conducted pseudovirus neutralization assays against the ancestral SARS-CoV-2 strain and contemporaneous Omicron BA.1 and BA.2 variants, allowing for parallel analyses of anti-Omicron titers as correlates of protection and more widely available ancestral-neutralizing titers.

Implications of all the available evidence

Overall, the results in this study, in combination with the prior available evidence, continue to point to serum neutralizing antibodies as an informative correlate of protection from overall and symptomatic infection. Titers against contemporaneous variants (BA.1 and BA.2 in this case), were protective at lower levels than those against the ancestral strain, but ancestral-neutralizing titer was still informative as a correlate of protection. Lastly, for any known vaccination or prior infection history studied with such an analysis, neutralizing antibodies appear to mediate protective effects of prior SARS-CoV-2 exposure on overall or symptomatic infection.

Neutralizing Antibody Immune Correlates for a Recombinant Protein Vaccine in the COVAIL Trial

For COVAIL recipients of a coronavirus disease 2019 (COVID-19) Sanofi booster vaccine, neutralizing antibody titers were assessed as a correlate of risk (CoR) of COVID-19. Peak and exposure-proximal titers were inverse CoRs with covariate-adjusted hazard ratios (95% confidence intervals) 0.30 (0.11, 0.78) and 0.25 (0.07, 0.85) per 10-fold increase in weighted average titer.

Neutralizing antibody immune correlates in COVAIL trial recipients of an mRNA second COVID-19 vaccine boost

Neutralizing antibody titer has been a surrogate endpoint for guiding COVID-19 vaccine approval and use, although the pandemic's evolution and the introduction of variant-adapted vaccine boosters raise questions as to this surrogate's contemporary performance. For 985 recipients of an mRNA second bivalent or monovalent booster containing various Spike inserts [Prototype (Ancestral), Beta, Delta, and/or Omicron BA.1 or BA.4/5] in the COVAIL trial (NCT05289037), titers against 5 strains were assessed as correlates of risk of symptomatic COVID-19 ("COVID-19") and as correlates of relative (Pfizer-BioNTech Omicron vs. Prototype) booster protection against COVID-19 over 6 months of follow-up during the BA.2-BA.5 Omicron-dominant period. Consistently across the Moderna and Pfizer-BioNTech vaccine platforms and across all variant Spike inserts assessed, both peak and exposure-proximal ("predicted-at-exposure") titers correlated with lower Omicron COVID-19 risk in individuals previously infected with SARS-CoV-2, albeit significantly less so in naïve individuals [e.g., exposure-proximal hazard ratio per 10-fold increase in BA.1 titer 0.74 (95% CI 0.59, 0.94) for naïve vs. 0.41 (95% CI 0.23, 0.64) for non-naïve; interaction p = 0.013]. Neutralizing antibody titer was a strong inverse correlate of Omicron COVID-19 in non-naïve individuals and a weaker correlate in naïve individuals, posing questions about how prior infection alters the neutralization correlate.

A bivalent COVID-19 mRNA vaccine elicited broad immune responses and protection against Omicron subvariants infection

Continuously emerging SARS-CoV-2 Omicron subvariants pose a threat thwarting the effectiveness of approved COVID-19 vaccines. Especially, the protection breadth and degree of these vaccines against antigenically distant Omicron subvariants is unclear. Here, we report the immunogenicity and efficacy of a bivalent mRNA vaccine, PTX-COVID19-M1.2 (M1.2), which encodes native spike proteins from Wuhan-Hu-1 (D614G) and Omicron BA.2.12.1, in mouse and hamster models. Both primary series and booster vaccination using M1.2 elicited potent and broad nAbs against Wuhan-Hu-1 (D614G) and some Omicron subvariants. Strong spike-specific T cell responses against Wuhan-Hu-1 and Omicron subvariants, including JN.1, were also induced. Vaccination with M1.2 protected animals from Wuhan-Hu-1 and multiple Omicron subvariants challenges. Interestingly, protection against XBB.1.5 lung infection did not correlate with nAb levels. These results indicate that M1.2 generated a broadly protective immune response against antigenically distant Omicron subvariants, and spike-specific T cells probably contributed to the breadth of the protection.

Immunogenicity and safety following a homologous booster dose of a SARS-CoV-2 recombinant spike protein vaccine with Matrix-MTM adjuvant (NVX-CoV2373) versus a primary series in people living with and without HIV-1 infection in South Africa: A randomized crossover phase 2a/2b trial

COVID-19 remains a global public health issue and an improved understanding of vaccine performance in immunocompromised individuals, including people living with HIV (PLWH), is needed. Initial data from the present study's pre-crossover/booster phase were previously reported. This phase 2a/b clinical trial in South Africa (2019nCoV-501/NCT04533399) revisits 1:1 randomly assigned HIV-negative adults (18-84 years) and medically stable PLWH (18-64 years) who previously received two NVX-CoV2373 doses (5 μg recombinant Spike protein with 50 μg Matrix-M™ adjuvant) or placebo. During the 6-month blinded crossover/booster phase, NVX-CoV2373 recipients could receive a single NVX-CoV2373 booster dose and placebo recipients a 2-dose NVX-CoV2373 primary series. NVX-CoV2373 safety and immunogenicity were assessed according to prior SARS-CoV-2 infection and HIV status. Post-crossover, 1900/3793 NVX-CoV2373 recipients were assigned another dose, and 1893/3793 placebo recipients were assigned NVX-CoV2373 primary series. Approximately 56% of the participants were SARS-CoV-2-seropositive ("seropositive") at crossover (6% PLWH). In seropositive participants (HIV-negative and PLWH), booster-dose anti-spike IgG, MN50 and hACE2 inhibition responses increased to similar levels, exceeding those in seronegative participants. In primary-series and booster cohorts, seronegative PLWH showed higher neutralizing responses (4.9- to 5.5-fold, respectively) versus peak pre-crossover primary-series responses. The safety profile was similar among the pre-crossover/booster phase groups; solicited and unsolicited adverse events were infrequent in all groups. A single NVX-CoV2373 booster dose substantially increased antibodies. All baseline seropositive participants showed higher immune responses than seronegative participants. These findings support use of NVX-CoV2373, including in immunocompromised individuals.

Early antiviral CD4+ and CD8+ T cells are associated with upper airway clearance of SARS-CoV-2

T cells are involved in protective immunity against numerous viral infections. Data regarding functional roles of human T cells in SARS-CoV-2 (SARS2) viral clearance in primary COVID-19 are limited. To address this knowledge gap, we assessed samples for associations between SARS2 upper respiratory tract viral RNA levels and early virus-specific adaptive immune responses for 95 unvaccinated clinical trial participants with acute primary COVID-19 aged 18-86 years old, approximately half of whom were considered at high risk for progression to severe COVID-19. Functionality and magnitude of acute SARS2-specific CD4+ and CD8+ T cell responses were evaluated, in addition to antibody responses. Most individuals with acute COVID-19 developed SARS2-specific T cell responses within 6 days of COVID-19 symptom onset. Early CD4+ T cell and CD8+ T cell responses were polyfunctional, and both strongly associated with reduced upper respiratory tract SARS2 viral RNA, independent of neutralizing antibody titers. Overall, these findings provide evidence for protective roles for circulating SARS2-specific CD4+ and CD8+ T cells during acute COVID-19.

Mechanisms and implications of IgG4 responses to SARS-CoV-2 and other repeatedly administered vaccines

Vaccine-induced immunoglobulin G (IgG) profiles can vary with respect to the predominant subclasses that characterize the response. Among IgG subclasses, IgG4 is reported to have anti-inflammatory properties, but can also exhibit reduced capacity for virus neutralization and activation of Fc-dependent effector functions. Here, we review evidence that IgG4 subclass responses can be disproportionately increased in response to some types of vaccines targeting an array of diseases, including pertussis, HIV, malaria, and COVID-19. The basis for enhanced IgG4 induction by vaccines is poorly understood but may be associated with platform- or dose regimen-specific differences in antigen exposure and/or cytokine stimulation. The clinical implications of vaccine-induced IgG4 responses remain uncertain, though collective evidence suggests that proportional increases in IgG4 might reduce vaccine antigen-specific immunity. Additional work is needed to determine underlying mechanisms and to elucidate what role IgG4 may play in modifications of vaccine-induced immunity to disease.

Immunogenicity and safety of SARS-CoV-2 recombinant spike protein vaccine in South African people living with and without HIV-1 infection: A phase 2 randomised trial

BACKGROUND

Response data for COVID-19 vaccines in immunosuppressed individuals are typically limited to standard dosing in small populations. Adjusting number or interval of doses may impact immune responses based on HIV status.

METHODS

This phase 2 randomised, observer-blinded, placebo-controlled South African study (2019nCoV-505/NCT05112848) enrolled medically stable people living with HIV (PLWH) and HIV-uninfected participants aged 18-65 years. PLWH were randomised 1:1:1 to receive NVX-CoV2373 on day 0 (D0) and either D21 (2-DoseD0/D21) or D70 (2-DoseD0/D70), or on D0, D21, and D70 (3-Dose). HIV-uninfected participants were randomised 1:1 to each 2-Dose regimen. PLWH were stratified into well-controlled and less-well-controlled subgroups. The primary immunologic endpoint included serum IgG and neutralising antibody responses (per geometric mean fold rise [GMFR] in titre and seroconversion rate) to ancestral SARS-CoV-2 at D35 (2-DoseD0/D21) and D84 (2-DoseD0/D70 and 3-Dose). The primary safety endpoints were participants with an unsolicited adverse event through D84, at D120, and at D180, or reactogenicity ≤7 days post-vaccination.

RESULTS

Of 288 PLWH, 98, 96, and 94 were randomised into the 2-DoseD0/D21, 2-DoseD0/D70, and 3-Dose groups, respectively; 96 HIV-uninfected participants were randomised to the 2-DoseD0/D21 (n = 47) or 2-DoseD0/D70 (n = 49) regimens. Most (>85%) of the population were SARS-CoV-2 positive at baseline. Ancestral anti-spike IgG GMFRs in PLWH and HIV-uninfected participants, respectively, were 12·4 and 12·9 (D35) and 12·2 and 13·6 (D84). Comparable outcomes occurred across dosing regimens and in well-controlled and less-well-controlled PLWH. Microneutralization GMFRs at D84 in PLWH and HIV-uninfected participants, respectively, were: 6·9 and 10·1 (2-DoseD0/D21), 11·0 and 11·3 (2-DoseD0/D70), and 17·2 (PLWH 3-Dose). Antibody responses against BA.1 trended similar to those against the ancestral virus. Safety outcomes were comparable among PLWH and HIV-uninfected participants.

CONCLUSION

This study demonstrated that NVX-CoV2373 produced consistent immunogenicity responses to SARS-CoV-2 among PLWH and HIV-uninfected participants, with no new safety signals.

First-in-Human Phase I Trial to Assess the Safety and Immunogenicity of an Orf Virus-Based COVID-19 Vaccine Booster

The emergence of SARS-CoV-2 has necessitated the development of versatile vaccines capable of addressing evolving variants. Prime-2-CoV_Beta, a novel Orf virus-based COVID-19 vaccine, was developed to express the SARS-CoV-2 spike and nucleocapsid antigens. This first-in-human, phase I, dose-finding clinical trial was conducted to assess the safety, reactogenicity, and immunogenicity of Prime-2-CoV_Beta as a booster in healthy adults. From June 2022 to June 2023, 60 participants in Germany received varying doses of Prime-2-CoV_Beta. The study demonstrated a favorable safety profile, with no serious adverse events (AEs) reported. All AEs were mild (107) or moderate (10), with the most common symptoms being pain at the injection site, fatigue, and headache. Immunogenicity assessments revealed robust vaccine-induced antigen-specific immune responses. High doses notably elicited significant increases in antibodies against the spike and nucleocapsid proteins as well as neutralizing antibodies against SARS-CoV-2 and its variants. Additionally, the vaccine did not induce ORFV-neutralizing antibodies, indicating the potential for repeated administration. In conclusion, Prime-2-CoV_Beta was safe, well tolerated, and immunogenic, demonstrating potential as a broadly protective vaccine against SARS-CoV-2 and its variants. These promising results support further evaluation of higher doses and additional studies to confirm efficacy and long-term protection. This trial was registered at ClinicalTrials, NCT05389319.

Development of Next-Generation COVID-19 Vaccines: Biomedical Advanced Research and Development Authority (BARDA-)-Supported Phase 2b Study Designs

In response to the coronavirus disease 2019 (COVID-19) pandemic, vaccines were quickly and successfully developed and deployed, saving millions of lives globally. While first-generation vaccines are safe and effective in preventing disease caused by SARS-CoV-2, next-generation vaccines have the potential to improve efficacy and safety. Vaccines delivered by a mucosal route may elicit greater protective immunity at respiratory surfaces, thereby reducing transmission. Inclusion of viral antigens in addition to the spike protein may enhance protection against emerging variants of concern. Next-generation vaccine platforms with a new mechanism of action may necessitate efficacy trials to fulfill regulatory requirements. The Biomedical Advanced Research and Development Authority (BARDA) will be supporting Phase 2b clinical trials of candidate next-generation vaccines. The primary endpoint will be improved efficacy in terms of symptomatic disease relative to a currently approved COVID-19 vaccine. In this paper, we discuss the planned endpoints and potential challenges to this complex program.

Modelling the Relative Vaccine Efficacy of ARCT-154, a Self-Amplifying mRNA COVID-19 Vaccine, versus BNT162b2 Using Immunogenicity Data

Background: Self-amplifying mRNA vaccines have the potential to increase the magnitude and duration of protection against COVID-19 by boosting neutralizing antibody titers and cellular responses. Methods: In this study, we used the immunogenicity data from a phase 3 randomized trial comparing the immunogenicity of ARCT-154, a self-amplifying mRNA COVID-19 vaccine, with BNT162b2 mRNA COVID-19 vaccine to estimate the relative vaccine efficacy (rVE) of the two vaccines over time in younger (<60 years) and older (≥60 years) adults. Results: By day 181 post-vaccination, the rVE against symptomatic and severe Wuhan-Hu-1 disease was 9.2-11.0% and 1.2-1.5%, respectively, across age groups whereas the rVE against symptomatic and severe Omicron BA.4/5 disease was 26.8-48.0% and 5.2-9.3%, respectively, across age groups. Sensitivity analysis showed that varying the threshold titer for 50% protection against severe disease up to 10% of convalescent sera revealed incremental benefits of ARCT-154 over BNT162b2, with an rVE of up to 28.0% against Omicron BA.4/5 in adults aged ≥60 year. Conclusions: Overall, the results of this study indicate that ARCT-154 elicits broader and more durable immunogenicity against SARS-CoV-2, translating to enhanced disease protection, particularly for older adults against Omicron BA.4/5.

SARS-CoV-2 correlates of protection from infection against variants of concern

Serum neutralizing antibodies (nAbs) induced by vaccination have been linked to protection against symptomatic and severe coronavirus disease 2019. However, much less is known about the efficacy of nAbs in preventing the acquisition of infection, especially in the context of natural immunity and against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immune-escape variants. Here we conducted mediation analysis to assess serum nAbs induced by prior SARS-CoV-2 infections as potential correlates of protection against Delta and Omicron infections, in rural and urban household cohorts in South Africa. We find that, in the Delta wave, D614G nAbs mediate 37% (95% confidence interval: 34-40%) of the total protection against infection conferred by prior exposure to SARS-CoV-2, and that protection decreases with waning immunity. In contrast, Omicron BA.1 nAbs mediate 11% (95% confidence interval: 9-12%) of the total protection against Omicron BA.1 or BA.2 infections, due to Omicron's neutralization escape. These findings underscore that correlates of protection mediated through nAbs are variant specific, and that boosting of nAbs against circulating variants might restore or confer immune protection lost due to nAb waning and/or immune escape. However, the majority of immune protection against SARS-CoV-2 conferred by natural infection cannot be fully explained by serum nAbs alone. Measuring these and other immune markers including T cell responses, both in the serum and in other compartments such as the nasal mucosa, may be required to comprehensively understand and predict immune protection against SARS-CoV-2.

Immune correlates analysis of the Imbokodo (HVTN 705/HPX2008) efficacy trial of a mosaic HIV-1 vaccine regimen evaluated in Southern African people assigned female sex at birth: a two-phase case-control study

BACKGROUND

The HVTN 705 Imbokodo trial of 2636 people without HIV and assigned female sex at birth, conducted in southern Africa, evaluated a heterologous HIV-1 vaccine regimen: mosaic adenovirus 26-based vaccine (Ad26.Mos4.HIV) at Months 0, 3, 6, 12 and alum-adjuvanted clade C gp140 at Months 6, 12. Per-protocol vaccine efficacy (VE) against HIV-1 diagnosis from seven to 24 months was 14.1% (95% CI: -22.0% to 39.5%). Immune correlates analysis was performed for markers selected based on prior evidence in efficacy trials and/or nonhuman primate models.

METHODS

Humoral and cellular immune response markers at Month 7 were evaluated as immune correlates of risk and of protection in a breakthrough case-control cohort (n = 52 cases, 246 non-cases). Primary markers were IgG binding to vaccine-strain gp140, IgG3 binding to diverse Env antigens (IgG3 Env breadth), IgG3 binding to diverse V1V2 antigens (IgG3 V1V2 breadth), antibody-dependent phagocytosis against the vaccine-strain gp140, Env-specific CD4+ and CD8+ T-cell responses, and multi-epitope functions.

FINDINGS

No immune markers were statistically significant correlates of risk. IgG3 V1V2 breadth trended toward an inverse association: hazard ratio 0.70 (95% CI: 0.36 to 1.35; p = 0.29) per 10-fold increase and 0.51 (95% CI: 0.21 to 1.24; p = 0.14) in a Cox model with all primary markers. The VE estimate was 11.8% (95% CI: -17.9% to 34.0%) at all IgG3 V1V2 breadth values below 667 weighted geometric mean net MFI; just above this value, the VE estimate sharply increased to 62.6% (95% CI: -17.9% to 89.6%), and further increased to 80.9% (95% CI: -17.9% to 99.5%) at 1471 MFI, the 95th percentile of the marker distribution. Mediation analysis yielded a VE of 35.7% (95% CI: 15.0% to 51.3%) attributable to the vaccine's impact on this marker.

INTERPRETATION

The trend in association of greater IgG3 V1V2 antibody breadth with lower likelihood of HIV acquisition is consistent with the identification of antibodies against V1V2 as immune correlates in three other HIV vaccine efficacy trials and suggests that a greater emphasis should be placed on studying this region in the HIV-1 envelope as a vaccine immunogen.

FUNDING

National Institute of Allergy and Infectious Diseases and Janssen Vaccines & Prevention BV.

Navigating the Landscape of B Cell Mediated Immunity and Antibody Monitoring in SARS-CoV-2 Vaccine Efficacy: Tools, Strategies and Clinical Trial Insights

Correlates of Protection (CoP) are biomarkers above a defined threshold that can replace clinical outcomes as primary endpoints, predicting vaccine effectiveness to support the approval of new vaccines or follow up studies. In the context of COVID-19 vaccination, CoPs can help address challenges such as demonstrating vaccine effectiveness in special populations, against emerging SARS-CoV-2 variants or determining the durability of vaccine-elicited immunity. While anti-spike IgG titres and viral neutralising capacity have been characterised as CoPs for COVID-19 vaccination, the contribution of other components of the humoral immune response to immediate and long-term protective immunity is less well characterised. This review examines the evidence supporting the use of CoPs in COVID-19 clinical vaccine trials, and how they can be used to define a protective threshold of immunity. It also highlights alternative humoral immune biomarkers, including Fc effector function, mucosal immunity, and the generation of long-lived plasma and memory B cells and discuss how these can be applied to clinical studies and the tools available to study them.

Antibody Persistence and Risk of COVID-19 Infection: Insights from Modeling

BACKGROUND

In this post hoc exploratory study of the APHP-COVIBOOST trial (NCT05124171), we used statistical modeling to describe the evolution of neutralizing antibody (nAb) titers over time, asses its impact on SARS-CoV-2 infection, and explore potential differences between three booster vaccine formulations (D614, B.1.351, and BNT162b2).

METHODS

Antibody titers were measured for 208 adult participants at day 28, 3 months, and 6 months using a microneutralization assay against different Omicron subvariants. We developed four specific Bayesian statistical models based on a core model, accounting for vaccine-specific antibody decline, boosting of nAb for breakthrough infection, and risk of infection according to nAb levels. The model findings were cross-verified using another validated microneutralization assay.

RESULTS

The decrease in nAb titers was significantly lower for the B.1.351 vaccine than for the other booster formulations. An inverse relationship was found between risk of infection upon exposure and nAb levels. With Omicron BA.1 data, these results translated into a positive relative vaccine efficacy against any infection over 6 months for the B.1.351 vaccine compared to the BNT162b2 (31%) and D614 (21%) vaccines.

CONCLUSIONS

Risk of infection decreased with increasing nAb titers for all vaccines. Statistical models predicted significantly better antibody persistence for the B.1.351 booster formulation compared to the other evaluated vaccines.

A Brighton Collaboration standardized template with key considerations for a benefit-risk assessment for the Comirnaty COVID-19 mRNA vaccine

The Brighton Collaboration Benefit-Risk Assessment of VAccines by TechnolOgy (BRAVATO) Working Group evaluates the safety and other key features of new platform technology vaccines, including nucleic acid (RNA and DNA) vaccines. This manuscript uses the BRAVATO template to report the key considerations for a benefit-risk assessment of the coronavirus disease 2019 (COVID-19) mRNA-based vaccine BNT162b2 (Comirnaty®, or Pfizer-BioNTech COVID-19 vaccine) including the subsequent Original/Omicron BA.1, Original/Omicron BA.4-5 and Omicron XBB.1.5 variant-adapted vaccines developed by BioNTech and Pfizer to protect against COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Initial Emergency Use Authorizations or conditional Marketing Authorizations for the original BNT162b2 vaccine were granted based upon a favorable benefit-risk assessment taking into account clinical safety, immunogenicity, and efficacy data, which was subsequently reconfirmed for younger age groups, and by real world evidence data. In addition, the favorable benefit-risk assessment was maintained for the bivalent vaccines, developed against newly arising SARS-CoV-2 variants, with accumulating clinical trial data.

Early antiviral CD4 and CD8 T cell responses and antibodies are associated with upper respiratory tract clearance of SARS-CoV-2

T cells are involved in protective immunity against numerous viral infections. Data regarding functional roles of human T cells in SARS-CoV-2 (SARS2) viral clearance in primary COVID-19 are limited. To address this knowledge gap, samples were assessed for associations between SARS2 upper respiratory tract viral RNA levels and early virus-specific adaptive immune responses for 95 unvaccinated clinical trial participants with acute primary COVID-19 aged 18-86 years old, approximately half of whom were considered high risk for progression to severe COVID-19. Functionality and magnitude of acute SARS2-specific CD4 and CD8 T cell responses were evaluated, in addition to antibody responses. Most individuals with acute COVID-19 developed SARS2-specific T cell responses within 6 days of COVID-19 symptom onset. Early CD4 T cell and CD8 T cell responses were polyfunctional, and both strongly associated with reduced upper respiratory tract SARS2 viral RNA, independent of neutralizing antibody titers. Overall, these findings provide evidence for protective roles for circulating SARS2-specific CD4 and CD8 T cells during acute COVID-19.

Anti-Spike IgG antibodies as correlates of protection against SARS-CoV-2 infection in the pre-Omicron and Omicron era

Anti-Spike IgG antibodies against SARS-CoV-2, which are elicited by vaccination and infection, are correlates of protection against infection with pre-Omicron variants. Whether this association can be generalized to infections with Omicron variants is unclear. We conducted a retrospective cohort study with 8457 blood donors in Tyrol, Austria, analyzing 15,340 anti-Spike IgG antibody measurements from March 2021 to December 2022 assessed by Abbott SARS-CoV-2 IgG II chemiluminescent microparticle immunoassay. Using a Bayesian joint model, we estimated antibody trajectories and adjusted hazard ratios for incident SARS-CoV-2 infection ascertained by self-report or seroconversion of anti-Nucleocapsid antibodies. At the time of their earliest available anti-Spike IgG antibody measurement (median November 23, 2021), participants had a median age of 46.0 years (IQR 32.8-55.2), with 45.3% being female, 41.3% having a prior SARS-CoV-2 infection, and 75.5% having received at least one dose of a COVID-19 vaccine. Among 6159 participants with endpoint data, 3700 incident SARS-CoV-2 infections with predominantly Omicron sublineages were recorded over a median of 8.8 months (IQR 5.7-12.4). The age- and sex-adjusted hazard ratio for SARS-CoV-2 associated with having twice the anti-Spike IgG antibody titer was 0.875 (95% credible interval 0.868-0.881) overall, 0.842 (0.827-0.856) during 2021, and 0.884 (0.877-0.891) during 2022 (all p < 0.001). The associations were similar in females and males (Pinteraction = 0.673) and across age (Pinteraction = 0.590). Higher anti-Spike IgG antibody titers were associated with reduced risk of incident SARS-CoV-2 infection across the entire observation period. While the magnitude of association was slightly weakened in the Omicron era, anti-Spike IgG antibody continues to be a suitable correlate of protection against newer SARS-CoV-2 variants.

Anti-spike antibody level is associated with the risk of clinical progression among subjects hospitalized with COVID-19 pneumonia: results from a retrospective cohort study

PURPOSE

Antibodies against SARS-CoV-2 spike (anti-S) may confer protection against symptomatic COVID-19. Whether their level predicts progression among those with COVID-19 pneumonia remains unclear.

METHODS

We conducted a retrospective cohort study to assess predictors of anti-S levels and whether anti-S titer is associated with death or mechanical ventilation (MV). Adults hospitalized for COVID-19 pneumonia between July 2021 and July 2022 were enrolled if anti-S had been measured within 72 h of admission. Predictors of anti-S level were explored using multivariable quantile regression. The association between anti-S levels and 30-day death/MV was investigated via multivariable logistic regression. Analyses were stratified by vaccine status.

RESULTS

The median anti-S level was 1370 BAU/ml in 328 vaccinated and 15.5 BAU/ml in 206 unvaccinated individuals. Among the vaccinated, shorter symptom duration (p = 0.001), hematological malignancies (p = 0.002), and immunosuppressive therapy (p = 0.004) were associated with lower anti-S levels. In the unvaccinated group, symptom duration was the only predictor of anti-S levels (p < 0.001). After 30 days, 134 patients experienced death or MV. Among vaccinated individuals, higher anti-S levels correlated significantly with lower death/MV risk (per log2 increase, OR 0.88, 95%CI 0.81-0.97), irrespective of age and solid malignancies. Among unvaccinated, a marginally protective effect was observed (OR 0.86, 95%CI 0.73-1.01), independent of age, immunosuppressive therapy, and diabetes. Adjustment for monoclonal antibody treatment strengthened the association (OR 0.81, 95%CI 0.68-0.96).

CONCLUSION

This study suggests that levels of anti-S antibodies can predict critical or fatal outcomes in COVID-19 pneumonia patients, regardless of vaccination. Whether anti-S Ab could guide risk assessment and vaccination boosting merits further evaluation.

Immunogenicity and Safety of Heterologous Omicron BA.1 and Bivalent SARS-CoV-2 Recombinant Spike Protein Booster Vaccines: A Phase 3 Randomized Clinical Trial

BACKGROUND

Mutations present in emerging SARS-CoV-2 variants permit evasion of neutralization with prototype vaccines. A novel Omicron BA.1 subvariant-specific vaccine (NVX-CoV2515) was tested alone or as a bivalent preparation with the prototype vaccine (NVX-CoV2373) to assess antibody responses to SARS-CoV-2.

METHODS

Participants aged 18 to 64 years immunized with 3 doses of prototype mRNA vaccines were randomized 1:1:1 to receive a single dose of NVX-CoV2515, NVX-CoV2373, or the bivalent mixture in a phase 3 study investigating heterologous boosting with SARS-CoV-2 recombinant spike protein vaccines. Immunogenicity was measured 14 and 28 days after vaccination for the SARS-CoV-2 Omicron BA.1 sublineage and ancestral strain. Safety profiles of vaccines were assessed.

RESULTS

Of participants who received trial vaccine (N = 829), those administered NVX-CoV2515 (n = 286) demonstrated a superior neutralizing antibody response to BA.1 vs NVX-CoV2373 (n = 274) at day 14 (geometric mean titer ratio, 1.6; 95% CI, 1.33-2.03). Seroresponse rates were 73.4% (91/124; 95% CI, 64.7-80.9) for NVX-CoV2515 vs 50.9% (59/116; 95% CI, 41.4-60.3) for NVX-CoV2373. All formulations were similarly well tolerated.

CONCLUSIONS

NVX-CoV2515 elicited a superior neutralizing antibody response against the Omicron BA.1 subvariant as compared with NVX-CoV2373 when administered as a fourth dose. Safety data were consistent with the established safety profile of NVX-CoV2373.

CLINICAL TRIALS REGISTRATION

ClinicalTrials.gov (NCT05372588).

Safety, reactogenicity, and immunogenicity of Ad26.COV2.S as homologous or heterologous COVID-19 booster vaccination: Results of a randomized, double-blind, phase 2 trial

COVID-19 vaccine boosters may optimize durability of protection against variants of concern (VOCs). In this randomized, double-blind, phase 2 trial, participants received 3 different dose levels of an Ad26.COV2.S booster (5 × 1010 vp [viral particles], 2.5 × 1010 vp, or 1 × 1010 vp) ≥6 months post-primary vaccination with either single-dose Ad26.COV2.S (homologous boost; n = 774) or 2-dose BNT162b2 (heterologous boost; n = 758). Primary endpoints were noninferiority of neutralizing antibody responses at Day 15 post-boost versus Day 29 post-primary vaccination. Secondary endpoints included reactogenicity/safety and neutralizing antibody responses to VOCs. All primary endpoints passed prespecified hierarchical noninferiority criteria by Day 15 post-boost. Geometric mean increases in neutralizing antibody titers against the D614G reference strain ranged from 5.5 to 6.8 at Day 15 for homologous boosting and 12.6 to 22.0 for heterologous boosting. For VOCs, heterologous boosting elicited higher neutralizing antibody responses than homologous boosting. Neutralizing antibody responses were dose-dependent and durable for ≥6 months post-boost. More solicited systemic adverse events occurred following heterologous versus homologous boosting. Trial Registration:ClinicalTrials.gov Identifier: NCT04999111.

Antibody Response to Symptomatic Infection With SARS-CoV-2 Omicron Variant Viruses, December 2021-June 2022

We describe humoral immune responses in 105 ambulatory patients with laboratory-confirmed SARS-CoV-2 Omicron variant infection. In dried blood spot (DBS) collected within 5 days of illness onset and during convalescence, we measured binding antibody (bAb) against ancestral spike protein receptor binding domain (RBD) and nucleocapsid (N) protein using a commercial multiplex bead assay. Geometric mean bAb concentrations against RBD increased by a factor of 2.5 from 1258 to 3189 units/mL and by a factor of 47 against N protein from 5.5 to 259 units/mL between acute illness and convalescence; lower concentrations were associated with greater geometric mean ratios. Paired DBS specimens may be used to evaluate humoral response to SARS-CoV-2 infection.

Validation of a Pseudovirus Neutralization Assay for Severe Acute Respiratory Syndrome Coronavirus 2: A High-Throughput Method for the Evaluation of Vaccine Immunogenicity

The evaluation of coronavirus disease 2019 (COVID-19) vaccine immunogenicity remains essential as the severe acute respiratory syncytial virus 2 (SARS-CoV-2) pandemic continues to evolve and as additional variants emerge. Neutralizing antibodies are a known correlate of protection for SARS-CoV-2 vaccines. A pseudovirus neutralization (PNT) assay was developed and validated at Novavax Clinical Immunology Laboratories to allow for the detection of neutralizing antibodies in vaccine clinical trial sera. The PNT assay was precise, accurate, linear, and specific in measuring SARS-CoV-2 neutralization titers in human serum for ancestral strain and the Omicron subvariants BA.5 and XBB.1.5, with an overall geometric coefficient of variation of ≤43.4%, a percent relative bias within the expected range of -60% to 150%, and a linearity value of R2 > 0.98 for all three strains. This pseudovirus assay will be useful for the analysis of vaccine clinical trial samples to assess vaccine immunogenicity. Future work will focus on modifying the assay for emerging variants, including XBB.1.16, EG.5.1, BA.2.86, and any other variants that emerge in the ongoing pandemic.

Immunogenicity and safety of a bivalent (omicron BA.5 plus ancestral) SARS-CoV-2 recombinant spike protein vaccine as a heterologous booster dose: interim analysis of a phase 3, non-inferiority, randomised, clinical trial

BACKGROUND

SARS-CoV-2 variants evade immunity despite vaccination with prototype COVID-19 vaccines or previous infection. The 2019nCoV-311 (part 2) study is evaluating immune responses after two booster doses of a vaccine containing the omicron BA.5 subvariant spike protein in adults previously vaccinated with a prototype mRNA vaccine. This interim analysis reports on day 28 immunogenicity and safety outcomes after one booster dose.

METHODS

In this phase 3, randomised, observer-blinded study conducted at 35 sites in Australia, medically stable, previously COVID-19-vaccinated (mRNA-based; ≥three doses) adults aged 18 years or older were enrolled and randomly allocated (1:1:1; via an interactive web response system) to receive two doses of bivalent (NVX-CoV2373 + NVX-CoV2540; bivalent group), authorised prototype (NVX-CoV2373; prototype group), or BA.5 (NVX-CoV2540; BA.5 group) vaccine. Only blinded personnel performed study assessments or had participant contact to collect data after study vaccination. Participants received vaccines containing 5 μg SARS-CoV-2 recombinant spike protein and 50 μg Matrix-M adjuvant, administered via a 0·5 mL intramuscular injection (2·5 μg of NVX-CoV2373 plus 2·5 μg of NVX-CoV2540 for the bivalent vaccine, prepared on-site as a 1:1 mixture). The coprimary endpoints include day 28 neutralising antibody geometric mean titre (GMT) ratios (GMTRs) to omicron BA.5 and the ancestral strain, and seroresponse rates to BA.5, in the bivalent and prototype groups. These endpoints were calculated in the per-protocol analysis set, which was defined as participants who had received a vaccine dose, had baseline and day 28 immunogenicity data, and were PCR-negative for SARS-CoV-2, with no major protocol deviations. The primary objective was to determine the primary outcome (antibody responses), which consisted of three comparisons: superiority of the bivalent versus prototype vaccine for neutralising antibody GMT to BA.5 (ie, lower bound of the GMTR 95% CI >1·0); non-inferiority of neutralising antibody seroresponse rate to BA.5 (ie, lower bound of the seroresponse rate 95% CI >-5%); and non-inferiority of neutralising antibody GMT to the ancestral strain (ie, lower bound of GMTR 95% CI >0·67). This trial was registered at ClinicalTrials.gov, number NCT05372588.

FINDINGS

Between March 22, 2023 and May 2, 2023, 837 participants were screened for eligibility and 766 were randomly allocated to receive the BA.5 (n=255), prototype (n=252), or bivalent (n=259) vaccine. After accounting for exclusions due to participants being baseline SARS-CoV-2-positive, having previous infection, or protocol deviations, the per-protocol analysis set included 694 participants (236 in BA.5 group, 227 in prototype group, and 231 in bivalent group). In this interim analysis (maximum follow-up 35 days after the first dose), the bivalent group, compared with the prototype group, had superior neutralising antibody responses to BA.5 (GMT 1017·8 [95% CI 891·0-1162·6] vs 515·1 [450·4-589·0]; GMTR 2·0 [1·69-2·33]) and a non-inferior seroresponse rate to BA.5 at day 28 (39·8% [33·5-46·5] vs 12·3% [8·4-17·3]; difference 27·5% [19·8-35·0]). The bivalent group also had non-inferior neutralising antibody responses to the ancestral strain (GMTR 1·0 [0·84-1·20]), compared with the prototype group. All vaccines were similarly well tolerated.

INTERPRETATION

All three coprimary endpoints were met in part 2 of the ongoing 2019nCoV-311 study. These data support the development of monovalent and/or bivalent vaccines for the most currently circulating variants, to optimise protection. With no new safety findings, further investigation of omicron-based subvariant vaccines is supported by the evidence.

FUNDING

Novavax.

Validation of a severe acute respiratory syndrome coronavirus 2 microneutralization assay for evaluation of vaccine immunogenicity

As variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continue to emerge, assessment of vaccine immunogenicity remains a critical factor to support continued vaccination. To this end, an in vitro microneutralization (MN50) assay was validated to quantitate SARS-CoV-2 neutralizing antibodies against prototype and variant strains (Beta, Delta, Omicron BA.1, Omicron BA.5, and XBB.1.5) in human serum. For the prototype strain, the MN50 assay met acceptance criteria for inter-/intra-assay precision, specificity, linearity, and selectivity. The assay was robust against changes to virus/serum incubation time, cell seeding density, virus content per well, cell passage number, and serum interference. Analyte in serum samples was stable up to five freeze/thaw cycles and for up to 12 months of storage at -80 ± 10 °C. Similar results were observed for the variant-adapted MN50 assays. The conversion factor to convert assay result units to WHO international standard units (IU/mL) was determined to be 0.62 for the prototype strain. This MN50 assay will be useful for vaccine immunogenicity analyses in clinical trial samples, enabling assessment of vaccine immunogenicity for ancestral and variant strains as variant-adapted vaccines are developed.

Mosaic sarbecovirus nanoparticles elicit cross-reactive responses in pre-vaccinated animals

Immunization with mosaic-8b [60-mer nanoparticles presenting 8 SARS-like betacoronavirus (sarbecovirus) receptor-binding domains (RBDs)] elicits more broadly cross-reactive antibodies than homotypic SARS-CoV-2 RBD-only nanoparticles and protects against sarbecoviruses. To investigate original antigenic sin (OAS) effects on mosaic-8b efficacy, we evaluated effects of prior COVID-19 vaccinations in non-human primates and mice on anti-sarbecovirus responses elicited by mosaic-8b, admix-8b (8 homotypics), or homotypic SARS-CoV-2 immunizations, finding greatest cross-reactivity for mosaic-8b. As demonstrated by molecular fate-mapping in which antibodies from specific cohorts of B cells are differentially detected, B cells primed by WA1 spike mRNA-LNP dominated antibody responses after RBD-nanoparticle boosting. While mosaic-8b- and homotypic-nanoparticles boosted cross-reactive antibodies, de novo antibodies were predominantly induced by mosaic-8b, and these were specific for variant RBDs with increased identity to RBDs on mosaic-8b. These results inform OAS mechanisms and support using mosaic-8b to protect COVID-19 vaccinated/infected humans against as-yet-unknown SARS-CoV-2 variants and animal sarbecoviruses with human spillover potential.

Serological Correlates of Protection Induced by COVID-19 Vaccination in the Working Age Population: A Systematic Review and Meta-Analysis

COVID-19 vaccines represent effective public health measures in contrasting the pandemic worldwide. However, protection at the individual-level, which is of crucial importance from an occupational health perspective, is commonly assessed by a serological correlate of protection (CoP) for SARS-CoV-2, which has not yet been determined. The emergence of variants of concern (VOCs) that have shown high rates of breakthrough infections has further complicated the understanding of immune protection against infection. To define a potential serological correlate of protection induced by the COVID-19 vaccination, a systematic review and meta-analysis was performed to summarize the evidence concerning the binding antibody concentration corresponding to a protective effect. Eighteen and four studies were included in the qualitative and quantitative analyses, respectively. The protection against infection was shown for anti-receptor-binding domain (RBD) titers ranging from 154 to 168.2 binding antibody units (BAU)/mL during the pre-Omicron period, while ranging from 1235 to 3035 BAU/mL in the Omicron period. Pooling the results from the studies concerning anti-RBD and anti-Spike antibody titer, we found a mean of 1341.5 BAU/mL and 1400.1 BAU/mL, respectively. These findings suggest that although a fixed serological threshold corresponding to protection against different SARS-CoV-2 variants is not yet definable, higher binding antibody concentrations are associated with increased protective effects.

Principles and therapeutic applications of adaptive immunity

Adaptive immunity provides protection against infectious and malignant diseases. These effects are mediated by lymphocytes that sense and respond with targeted precision to perturbations induced by pathogens and tissue damage. Here, we review key principles underlying adaptive immunity orchestrated by distinct T cell and B cell populations and their extensions to disease therapies. We discuss the intracellular and intercellular processes shaping antigen specificity and recognition in immune activation and lymphocyte functions in mediating effector and memory responses. We also describe how lymphocytes balance protective immunity against autoimmunity and immunopathology, including during immune tolerance, response to chronic antigen stimulation, and adaptation to non-lymphoid tissues in coordinating tissue immunity and homeostasis. Finally, we discuss extracellular signals and cell-intrinsic programs underpinning adaptive immunity and conclude by summarizing key advances in vaccination and engineering adaptive immune responses for therapeutic interventions. A deeper understanding of these principles holds promise for uncovering new means to improve human health.

Plant stanol consumption increases anti-COVID-19 antibody responses, independent of changes in serum cholesterol concentrations: a randomized controlled trial

BACKGROUND

People with overweight/obesity generally have impaired immune responses, resulting among others in increased risk of severe complaints and hospitalization after infections with severe acute respiratory syndrome coronavirus 2 (COVID-19), as well as decreased antibody production after vaccinations. Plant stanol ester previously increased the combined IgM/IgG antibody titers toward a hepatitis A vaccination in patients with allergic asthma, but the underlying mechanism is unknown.

OBJECTIVES

We evaluated whether plant stanol ester consumption improved the immune response in subjects with overweight/obesity after a COVID-19 vaccination.

METHODS

A double-blind, randomized, placebo-controlled trial was performed. Thirty-two subjects with overweight/obesity consumed products with added plant stanols (4 g/d; provided as plant stanol ester) or control ≥2 wk before receiving their COVID-19 vaccination until 4 wk after vaccination. Antibody titers were analyzed weekly and statistically analyzed using mixed models. Serum metabolic markers and cytokine profiles were also analyzed.

RESULTS

IgM concentrations against the COVID-19 Spike protein were increased in the plant stanol ester group compared with the control group, with the largest difference observed 2 wk after vaccination [31.2 (0.43, 62.1) BAU/mL, or +139%; Group × Time: P = 0.031]. Subjects that produced very low IgM antibodies produced, as expected, hardly any IgG antibodies. In those with IgG seroconversion, IgG Spike concentrations were also increased in the plant stanol ester group compared with the control group [71.3 (2.51, 140.1) BAU/mL; Group P = 0.043]. Stimulated cytokine concentrations decreased in the plant stanol ester group compared with the control group in all 3 cytokine domains (that is, proinflammatory, T helper [Th1]/Th17, and Th2/regulatory T cells). Between-group differences in serum LDL cholesterol or other metabolic markers were not observed.

CONCLUSIONS

Consuming plant stanols (4 g/d) affects immune responses to COVID-19 vaccinations, translating into increased serum anti-COVID-19 IgM concentrations in subjects with overweight/obesity. Only in IgG seroconverted subjects, serum anti-COVID-19 IgG concentrations also increase. These effects are independent of reductions in LDL cholesterol. These results suggest that this high-risk group for COVID-19 complications could benefit from plant stanol consumption. This trial was registered at clinicaltrials.gov as NCT04844346.

Beta-variant recombinant booster vaccine elicits broad cross-reactive neutralization of SARS-CoV-2 including Omicron variants

Background

SARS-CoV-2 Omicron lineage contains variants with multiple sequence mutations relative to the ancestral strain particularly in the viral spike gene. These mutations are associated inter alia with loss of neutralization sensitivity to sera generated by immunization with vaccines targeting ancestral strains or prior infection with circulating (non-Omicron) variants. Here we present a comparison of vaccine formulation elicited cross neutralization responses using two different assay readouts from a subpopulation of a Phase II/III clinical trial.

Methods

Human sera from a Phase II/III trial (NCT04762680) was collected and evaluated for neutralizing responses to SARS-CoV-2 spike antigen protein vaccines formulated with AS03 adjuvant, following a primary series of two-doses of ancestral strain vaccine in individuals who were previously unvaccinated or as an ancestral or variant strain booster vaccine among individuals previously vaccinated with the mRNA BNT162b2 vaccine.

Results

We report that a neutralizing response to Omicron BA.1 is induced by the two-dose primary series in 89% of SARS-CoV-2-seronegative individuals. A booster dose of each vaccine formulation raises neutralizing antibody titers that effectively neutralizes Omicron BA.1 and BA.4/5 variants. Responses are highest after the monovalent Beta variant booster and similar in magnitude to human convalescent plasma titers.

Conclusion

The findings of this study suggest the possibility to generate greater breadth of cross-neutralization to more recently emerging viral variants through use of a diverged spike vaccine in the form of a Beta variant booster vaccine.

Quantifying how single dose Ad26.COV2.S vaccine efficacy depends on Spike sequence features

In the ENSEMBLE randomized, placebo-controlled phase 3 trial (NCT04505722), estimated single-dose Ad26.COV2.S vaccine efficacy (VE) was 56% against moderate to severe-critical COVID-19. SARS-CoV-2 Spike sequences were determined from 484 vaccine and 1,067 placebo recipients who acquired COVID-19. In this set of prespecified analyses, we show that in Latin America, VE was significantly lower against Lambda vs. Reference and against Lambda vs. non-Lambda [family-wise error rate (FWER) p < 0.05]. VE differed by residue match vs. mismatch to the vaccine-insert at 16 amino acid positions (4 FWER p < 0.05; 12 q-value ≤ 0.20); significantly decreased with physicochemical-weighted Hamming distance to the vaccine-strain sequence for Spike, receptor-binding domain, N-terminal domain, and S1 (FWER p < 0.001); differed (FWER ≤ 0.05) by distance to the vaccine strain measured by 9 antibody-epitope escape scores and 4 NTD neutralization-impacting features; and decreased (p = 0.011) with neutralization resistance level to vaccinee sera. VE against severe-critical COVID-19 was stable across most sequence features but lower against the most distant viruses.

One-year follow-up of the immunogenicity and safety of a primary series of the NVX-CoV2373 (TAK-019) vaccine in healthy Japanese adults: Final report of a phase I/II randomized controlled trial

BACKGROUND

In the interim report of this phase I/II randomized, placebo-controlled trial in Japanese adults, a two-dose primary series of NVX-CoV2373 (5 µg SARS-CoV-2 recombinant nanoparticle spike protein [rS]; 50 µg Matrix-M) administered 21 days apart induced robust anti-SARS-CoV-2 immune responses up to day 50 and had an acceptable safety profile.

METHODS

Following the double-blind phase of this study (day 1-50), participants were informed about their assignment to NVX-CoV2373 or placebo, and their reconsent was required for continuation in the open-label phase (day 51-387). This final report evaluated immunogenicity on days 202 and 387, and safety findings from the 1-year follow-up.

RESULTS

In total, 131/150 participants in the NVX-CoV2373 arm and 4/50 in the placebo arm completed the study. The most common reason for discontinuation was because the participant requested a publicly available COVID-19 vaccine. At 6 months and 1 year after the second vaccine dose, both the geometric mean titres of anti-SARS-CoV-2 rS serum immunoglobulin G and serum neutralizing antibodies against the SARS-CoV-2 ancestral strain were numerically higher than before the second dose. There were no deaths, adverse events (AEs) leading to participant withdrawal, or AEs of special interest throughout the trial. During follow-up, 2.0 % (1/50) of participants in the placebo arm reported COVID-19 approximately 1 month after the second vaccine dose (serious AE requiring hospitalisation, already presented in the interim report) and 2.7 % (4/150) in the NVX-CoV2373 arm after approximately 10 months (mild [2/4] or moderate [2/4] in severity).

DISCUSSION

A primary series of NVX-CoV2373 induced persistent immune responses up to 1 year after the second dose. The vaccine was well tolerated and had an acceptable safety profile. We believe our findings offer important insights for determining dosing intervals between primary and booster vaccinations.

Immunogenicity and safety of a second heterologous booster dose of NVX-CoV2373 (TAK-019) in healthy Japanese adults who had previously received a primary series of COVID-19 mRNA vaccine: Interim analysis report of a phase 3 open-label trial

BACKGROUND

The phase 3, single-arm, open-label TAK-019-3001 study assessed two heterologous booster doses of NVX-CoV2373 administered 5 months apart in healthy Japanese adults who had completed a primary series of a COVID-19 mRNA vaccine 6-12 months previously. In the main part of this study, a first booster induced rapid and robust anti-SARS-CoV-2 immune responses, addressing waning immunity in participants.

METHODS

This interim analysis evaluated the immunogenicity and safety of a second booster in the extension part of this study including comparisons with the first booster. Immunogenicity was assessed on extension day (ED) 1 (before vaccination) and ED15. Solicited and unsolicited adverse events occurring in the 7 and 28 days, respectively, after vaccination were assessed.

RESULTS

Of the 150 participants who received a first NVX-CoV2373 booster, 129 were administered a second booster on ED1. Participant characteristics were consistent between the main and extension parts of the study. Titres of anti-SARS-CoV-2 rS serum immunoglobulin G and serum neutralizing antibodies against the SARS-CoV-2 ancestral strain at ED15 were 4.0- and 3.0-fold higher, respectively, than those observed 5 months after the first booster on ED1, and 3.0- and 1.4-fold higher, respectively, than those observed 14 days after the first booster on day 15. The proportions of participants who experienced solicited local and systemic adverse events (AEs) in the 7 days after the second booster were 73.6 % and 51.2 %, respectively: most were of grade 2 severity or lower. Seven percent of participants experienced unsolicited AEs in the 28 days after the second booster: all were unrelated to the treatment. There were no deaths or AEs leading to study discontinuation.

DISCUSSION

A second heterologous NVX-CoV2373 booster in healthy Japanese adults induced more robust anti-SARS-CoV-2 immune responses than the first booster. The second booster was well tolerated. No new safety concerns were identified.

Antibody and B Cell Responses to SARS-CoV-2 Infection and Vaccination: The End of the Beginning

As the COVID-19 pandemic has evolved during the past years, interactions between human immune systems, rapidly mutating and selected SARS-CoV-2 viral variants, and effective vaccines have complicated the landscape of individual immunological histories. Here, we review some key findings for antibody and B cell-mediated immunity, including responses to the highly mutated omicron variants; immunological imprinting and other impacts of successive viral antigenic variant exposures on antibody and B cell memory; responses in secondary lymphoid and mucosal tissues and non-neutralizing antibody-mediated immunity; responses in populations vulnerable to severe disease such as those with cancer, immunodeficiencies, and other comorbidities, as well as populations showing apparent resistance to severe disease such as many African populations; and evidence of antibody involvement in postacute sequelae of infection or long COVID. Despite the initial phase of the pandemic ending, human populations will continue to face challenges presented by this unpredictable virus.

Broadly neutralizing antibody induction by non-stabilized SARS-CoV-2 Spike mRNA vaccination in nonhuman primates

Immunization with mRNA or viral vectors encoding spike with diproline substitutions (S-2P) has provided protective immunity against severe COVID-19 disease. How immunization with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) spike elicits neutralizing antibodies (nAbs) against difficult-to-neutralize variants of concern (VOCs) remains an area of great interest. Here, we compare immunization of macaques with mRNA vaccines expressing ancestral spike either including or lacking diproline substitutions, and show the diproline substitutions were not required for protection against SARS-CoV-2 challenge or induction of broadly neutralizing B cell lineages. One group of nAbs elicited by the ancestral spike lacking diproline substitutions targeted the outer face of the receptor binding domain (RBD), neutralized all tested SARS-CoV-2 VOCs including Omicron XBB.1.5, but lacked cross-Sarbecovirus neutralization. Structural analysis showed that the macaque broad SARS-CoV-2 VOC nAbs bound to the same epitope as a human broad SARS-CoV-2 VOC nAb, DH1193. Vaccine-induced antibodies that targeted the RBD inner face neutralized multiple Sarbecoviruses, protected mice from bat CoV RsSHC014 challenge, but lacked Omicron variant neutralization. Thus, ancestral SARS-CoV-2 spike lacking proline substitutions encoded by nucleoside-modified mRNA can induce B cell lineages binding to distinct RBD sites that either broadly neutralize animal and human Sarbecoviruses or recent Omicron VOCs.

Stochastic interventional approach to assessing immune correlates of protection: Application to the COVE messenger RNA-1273 vaccine trial

BACKGROUND

Stochastic interventional vaccine efficacy (SVE) analysis is a new approach to correlate of protection (CoP) analysis of a phase III trial that estimates how vaccine efficacy (VE) would change under hypothetical shifts of an immune marker.

METHODS

We applied nonparametric SVE methodology to the COVE trial of messenger RNA-1273 vs placebo to evaluate post-dose 2 pseudovirus neutralizing antibody (nAb) titer against the D614G strain as a CoP against COVID-19. Secondly, we evaluated the ability of these results to predict VE against variants based on shifts of geometric mean titers to variants vs D614G. Prediction accuracy was evaluated by 13 validation studies, including 12 test-negative designs.

RESULTS

SVE analysis of COVE supported post-dose 2 D614G titer as a CoP: estimated VE ranged from 66.9% (95% confidence interval: 36.2, 82.8%) to 99.3% (99.1, 99.4%) at 10-fold decreased or increased titer shifts, respectively. The SVE estimates only weakly predicted variant-specific VE estimates (concordance correlation coefficient 0.062 for post 2-dose VE).

CONCLUSION

SVE analysis of COVE supports nAb titer as a CoP for messenger RNA vaccines. Predicting variant-specific VE proved difficult due to many limitations. Greater anti-Omicron titers may be needed for high-level protection against Omicron vs anti-D614G titers needed for high-level protection against pre-Omicron COVID-19.

Antibody response to symptomatic infection with SARS-CoV-2 Omicron variant viruses, December 2021-June 2022

To describe humoral immune responses to symptomatic SARS-CoV-2 infection, we assessed immunoglobulin G binding antibody levels using a commercial multiplex bead assay against SARS-CoV-2 ancestral spike protein receptor binding domain (RBD) and nucleocapsid protein (N). We measured binding antibody units per mL (BAU/mL) during acute illness within 5 days of illness onset and during convalescence in 105 ambulatory patients with laboratory-confirmed SARS-CoV-2 infection with Omicron variant viruses. Comparing acute- to convalescent phase antibody concentrations, geometric mean anti-N antibody concentrations increased 47-fold from 5.5 to 259 BAU/mL. Anti-RBD antibody concentrations increased 2.5-fold from 1258 to 3189 BAU/mL.

XBB.1.5 spike protein COVID-19 vaccine induces broadly neutralizing and cellular immune responses against EG.5.1 and emerging XBB variants

Monovalent SARS-CoV-2 Prototype (Wuhan-Hu-1) and bivalent (Prototype + BA.4/5) COVID-19 vaccines have demonstrated a waning of vaccine-mediated immunity highlighted by lower neutralizing antibody responses against SARS-CoV-2 Omicron XBB sub-variants. The reduction of humoral immunity due to the rapid evolution of SARS-CoV-2 has signaled the need for an update to vaccine composition. A strain change for all authorized/approved vaccines to a monovalent composition with Omicron subvariant XBB.1.5 has been supported by the WHO, EMA, and FDA. Here, we demonstrate that immunization with a monovalent recombinant spike protein COVID-19 vaccine (Novavax, Inc.) based on the subvariant XBB.1.5 induces neutralizing antibodies against XBB.1.5, XBB.1.16, XBB.2.3, EG.5.1, and XBB.1.16.6 subvariants, promotes higher pseudovirus neutralizing antibody titers than bivalent (Prototype + XBB.1.5) vaccine, induces SARS-CoV-2 spike-specific Th1-biased CD4 + T-cell responses against XBB subvariants, and robustly boosts antibody responses in mice and nonhuman primates primed with a variety of monovalent and bivalent vaccines. Together, these data support updating the Novavax vaccine to a monovalent XBB.1.5 formulation for the 2023-2024 COVID-19 vaccination campaign.

Distinct receptor binding domain IgG thresholds predict protective host immunity across SARS-CoV-2 variants and time

SARS-CoV-2 neutralising antibodies provide protection against COVID-19. Evidence from early vaccine trials suggested binding antibody thresholds could serve as surrogate markers of neutralising capacity, but whether these thresholds predict sufficient neutralising capacity against variants of concern (VOCs), and whether this is impacted by vaccine or infection history remains unclear. Here we analyse individuals recovered from, vaccinated or with hybrid immunity against SARS-CoV-2. An NT50 ≥ 100 IU confers protection in vaccine trials, however, as VOC induce a reduction in NT50, we use NT50 ≥ 1000 IU as a cut off for WT NT50 that would retain neutralisation against VOC. In unvaccinated convalescent participants, a receptor binding domain (RBD) IgG of 456 BAU/mL predicts an NT50 against WT of 1000 IU with an accuracy of 80% (95%CI 73-86%). This threshold maintains accuracy in determining loss of protective immunity against VOC in two vaccinated cohorts. It predicts an NT50 < 100 IU against Beta with an accuracy of 80% (95%CI 67-89%) in 2 vaccine dose recipients. In booster vaccine recipients with a history of COVID-19 (hybrid immunity), accuracy is 87% (95%CI 77-94%) in determining an NT50 of <100 IU against BA.5. This analysis provides a discrete threshold that could be used in future clinical studies.

The breadth of the neutralizing antibody response to original SARS-CoV-2 infection is linked to the presence of Long COVID symptoms

The associations between longitudinal dynamics and the breadth of SARS-CoV-2 neutralizing antibody (nAb) response with various Long COVID phenotypes before vaccination are not known. The capacity of antibodies to cross-neutralize a variety of viral variants may be associated with ongoing pathology and persistent symptoms. We measured longitudinal neutralizing and cross-neutralizing antibody responses to pre- and post-SARS-CoV-2 Omicron variants in participants infected early in the COVID-19 pandemic, before widespread rollout of SARS-CoV-2 vaccines. Cross-sectional regression models adjusted for clinical covariates and longitudinal mixed-effects models were used to determine the impact of the breadth and rate of decay of neutralizing responses on the development of Long COVID symptoms, as well as Long COVID phenotypes. We identified several novel relationships between SARS-CoV-2 antibody neutralization and the presence of Long COVID symptoms. Specifically, we show that, although nAb responses to the original, infecting strain of SARS-CoV-2 were not associated with Long COVID in cross-sectional analyses, cross-neutralization ID50 levels to the Omicron BA.5 variant approximately 4 months following acute infection was independently and significantly associated with greater odds of Long COVID and with persistent gastrointestinal and neurological symptoms. Longitudinal modeling demonstrated significant associations in the overall levels and rates of decay of neutralization capacity with Long COVID phenotypes. A higher proportion of participants had antibodies capable of neutralizing Omicron BA.5 compared with BA.1 or XBB.1.5 variants. Our findings suggest that relationships between various immune responses and Long COVID are likely complex but may involve the breadth of antibody neutralization responses.

Immunogenicity and safety of AZD2816, a beta (B.1.351) variant COVID-19 vaccine, and AZD1222 (ChAdOx1 nCoV-19) as third-dose boosters for previously vaccinated adults: a multicentre, randomised, partly double-blinded, phase 2/3 non-inferiority immunobridging study in the UK and Poland

BACKGROUND

This study aimed to evaluate AZD2816, a variant-updated COVID-19 vaccine expressing the full-length SARS-CoV-2 beta (B.1.351) variant spike protein that is otherwise similar to AZD1222 (ChAdOx1 nCoV-19), and AZD1222 as third-dose boosters.

METHODS

This phase 2/3, partly double-blinded, randomised, active-controlled study was done at 19 sites in the UK and four in Poland. Adult participants who had received a two-dose AZD1222 or mRNA vaccine primary series were randomly assigned by means of an Interactive Response Technology-Randomisation and Trial Supply Management system (1:1 within each primary-series cohort, stratified by age, sex, and comorbidities) to receive AZD1222 or AZD2816 (intramuscular injection; 5 × 1010 viral particles). Participants, investigators, and all sponsor staff members involved in study conduct were masked to randomisation. AZD1222 and AZD2816 doses were prepared by unmasked study staff members. The primary objectives were to evaluate safety and humoral immunogenicity (non-inferiority of day-29 pseudovirus neutralising antibody geometric mean titre [GMT] against ancestral SARS-CoV-2: AZD1222 booster vs AZD1222 primary series [historical controls]; margin 0·67; SARS-CoV-2-seronegative participants). This study is registered with ClinicalTrials.gov, NCT04973449, and is completed.

FINDINGS

Between June 27 and Sept 30, 2021, 1394 participants of the 1741 screened were randomly assigned to AZD1222 or AZD2816 following an AZD1222 (n=373, n=377) or mRNA vaccine (n=322, n=322) primary series. In SARS-CoV-2-seronegative participants receiving AZD1222 or AZD2816, 78% and 80% (AZD1222 primary series) and 90% and 93%, respectively (mRNA vaccine primary series) reported solicited adverse events to the end of day 8; 2%, 2%, 1%, and 1% had serious adverse events and 12%, 12%, 10%, and 11% had adverse events of special interest, respectively, to the end of day 180. The primary immunogenicity non-inferiority endpoint was met: day-29 neutralising antibody GMT ratios (ancestral SARS-CoV-2) were 1·02 (95% CI 0·90-1·14) and 3·47 (3·09-3·89) with AZD1222 booster versus historical controls (AZD1222 and mRNA vaccine primary series, respectively). Responses against beta were greater with AZD2816 versus AZD1222 (GMT ratios, AZD1222, mRNA vaccine primary series 1·84 [1·63-2·08], 2·22 [1·99-2·47]).

INTERPRETATION

Both boosters were well tolerated, with immunogenicity against ancestral SARS-CoV-2 similar to AZD1222 primary-series vaccination. AZD2816 gave greater immune responses against beta versus AZD1222.

FUNDING

AstraZeneca.

Clinical Utility of SARS-CoV-2 Serological Testing and Defining a Correlate of Protection

Herein, we review established clinical use cases for SARS-CoV-2 antibody measures, which include diagnosis of recent prior infection, isolating high titer convalescent plasma, diagnosing multisystem inflammatory syndrome in children (MIS-C), and booster dosing in the immunosuppressed and other populations. We then address whether an antibody correlate of protection (CoP) for SARS-CoV-2 has been successfully defined with the following considerations: Antibody responses in the immunocompetent, vaccine type, variants, use of binding antibody tests vs. neutralization tests, and endpoint measures. In the transition from the COVID-19 pandemic to endemic, there has been much interest in defining an antibody CoP. Due to the high mutability of respiratory viruses and our current knowledge of SARS-CoV-2 variants defining a CoP for prevention of infection is unrealistic. However, a CoP may be defined for prevention of severe disease requiring hospitalization and/or death. Most SARS-CoV-2 CoP research has focused on neutralization measurements. However, there can be significant differences in neutralization test methods, and disparate responses to new variants depending on format. Furthermore, neutralization assays are often impractical for high throughput applications (e.g., assessing humoral immune response in populations or large cohorts). Nevertheless, CoP studies using neutralization measures are reviewed to determine where there is consensus. Alternatively, binding antibody tests could be used to define a CoP. Binding antibody assays tend to be highly automatable, high throughput, and therefore practical for large population applications. Again, we review studies for consensus on binding antibody responses to vaccines, focusing on standardized results. Binding antibodies directed against the S1 receptor binding domain (S1-RBD) of the viral spike protein can provide a practical, indirect measure of neutralization. Initially, a response for S1-RBD antibodies may be selected that reflects the peak response in immunocompetent populations and may serve as a target for booster dosing in the immunocompromised. From existing studies reporting peak S1-RBD responses in standardized units, an approximate range of 1372-2744 BAU/mL for mRNA and recombinant protein vaccines was extracted that could serve as an initial CoP target. This target would need to be confirmed and potentially adjusted for updated vaccines, and almost certainly for other vaccine formats (i.e., viral vector). Alternatively, a threshold or response could be defined based on outcomes over time (i.e., prevention of severe disease). We also discuss the precedent for clinical measurement of antibodies for vaccine-preventable diseases (e.g., hepatitis B). Lastly, cellular immunity is briefly addressed for its importance in the nature and durability of protection.

Stochastic Interventional Vaccine Efficacy and Principal Surrogate Analyses of Antibody Markers as Correlates of Protection against Symptomatic COVID-19 in the COVE mRNA-1273 Trial

The COVE trial randomized participants to receive two doses of mRNA-1273 vaccine or placebo on Days 1 and 29 (D1, D29). Anti-SARS-CoV-2 Spike IgG binding antibodies (bAbs), anti-receptor binding domain IgG bAbs, 50% inhibitory dilution neutralizing antibody (nAb) titers, and 80% inhibitory dilution nAb titers were measured at D29 and D57. We assessed these markers as correlates of protection (CoPs) against COVID-19 using stochastic interventional vaccine efficacy (SVE) analysis and principal surrogate (PS) analysis, frameworks not used in our previous COVE immune correlates analyses. By SVE analysis, hypothetical shifts of the D57 Spike IgG distribution from a geometric mean concentration (GMC) of 2737 binding antibody units (BAU)/mL (estimated vaccine efficacy (VE): 92.9% (95% CI: 91.7%, 93.9%)) to 274 BAU/mL or to 27,368 BAU/mL resulted in an overall estimated VE of 84.2% (79.0%, 88.1%) and 97.6% (97.4%, 97.7%), respectively. By binary marker PS analysis of Low and High subgroups (cut-point: 2094 BAU/mL), the ignorance interval (IGI) and estimated uncertainty interval (EUI) for VE were [85%, 90%] and (78%, 93%) for Low compared to [95%, 96%] and (92%, 97%) for High. By continuous marker PS analysis, the IGI and 95% EUI for VE at the 2.5th percentile (519.4 BAU/mL) vs. at the 97.5th percentile (9262.9 BAU/mL) of D57 Spike IgG concentration were [92.6%, 93.4%] and (89.2%, 95.7%) vs. [94.3%, 94.6%] and (89.7%, 97.0%). Results were similar for other D29 and D57 markers. Thus, the SVE and PS analyses additionally support all four markers at both time points as CoPs.

The role of vaccination route with an adenovirus-vectored vaccine in protection, viral control, and transmission in the SARS-CoV-2/K18-hACE2 mouse infection model

Introduction

Vaccination is the most effective mechanism to prevent severe COVID-19. However, breakthrough infections and subsequent transmission of SARS-CoV-2 remain a significant problem. Intranasal vaccination has the potential to be more effective in preventing disease and limiting transmission between individuals as it induces potent responses at mucosal sites.

Methods

Utilizing a replication-deficient adenovirus serotype 5-vectored vaccine expressing the SARS-CoV-2 RBD (AdCOVID) in homozygous and heterozygous transgenic K18-hACE2, we investigated the impact of the route of administration on vaccine immunogenicity, SARS-CoV-2 transmission, and survival.

Results

Mice vaccinated with AdCOVID via the intramuscular or intranasal route and subsequently challenged with SARS-CoV-2 showed that animals vaccinated intranasally had improved cellular and mucosal antibody responses. Additionally, intranasally vaccinated animals had significantly better viremic control, and protection from lethal infection compared to intramuscularly vaccinated animals. Notably, in a novel transmission model, intranasal vaccination reduced viral transmission to naïve co-housed mice compared to intramuscular vaccination.

Discussion

Our data provide convincing evidence for the use of intranasal vaccination in protecting against SARS-CoV-2 infection and transmission.