Persistence of immune responses after heterologous and homologous third COVID-19 vaccine dose schedules in the UK: eight-month analyses of the COV-BOOST trial

SARS-CoV-2 Vaccines and Multiple Sclerosis: An Update

The highly contagious zoonosis coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was declared a pandemic by the World Health Organization on March 11, 2020, and has led to a global health crisis with nearly 777 million confirmed infections and over 7 million deaths worldwide by November 10, 2024.1-3 Over time, various variants emerged, with Omicron and its sublines dominating the world over the past 3 years.4 In addition, there is increasing evidence regarding the immune response of SARS-CoV-2 vaccines, especially for people with multiple sclerosis (MS) receiving disease-modifying therapies. Hence, with this review, we aim to provide an updated overview and recommendations for clinical practice regarding MS and SARS-CoV-2 vaccines, including efficacy and safety, SARS-CoV-2 variants, vaccine hesitancy, and the immune response under treatment with respective disease-modifying therapies.

SARS-CoV-2 infection in the Indigenous Pataxó community of Southern Bahia, Brazil: second wave of transmission and vaccine effects

Indigenous people are at risk of several infectious diseases, including viruses that affect the respiratory system. In a previous study, we demonstrated how the Pataxó ethnic group, in the southernmost region of Bahia State, Brazil, was disproportionately affected during the first wave of COVID-19. Here, we provide an overview of how this community was affected by the second wave of the disease, evaluating the impact of vaccination on SARS-CoV-2 transmission. Prospective study data was grouped by Epidemiological Weeks 3/2021-43/2022, during which vaccine effects were analyzed and new variants of concern (VOC) emerged. The second wave produced a decreasing trimodal moving average curve, with an incidence rate of 4,407.2/100,000 inhabitants. Mobility and precarious work situations linked to tourism and craft trade increased infection rates in some villages. Risk factors for infection and severity (female sex, older age, and comorbidities) were determinants, but mortality was lower. Individuals with two doses of vaccine (Vac) developed more symptoms than the unvaccinated, but were less likely to have dyspnea. The mean time for COVID-19 symptoms to develop was longer in those with Vac (x̅ = 27 weeks) compared to those who received only one dose (x̅ = 12 weeks, p ≤ 0.001). Vac individuals who received booster shots, VacB1 and VacB2, had infection rates of 7.4% and 0%, respectively. The detrimental impact of COVID-19 once again highlights the persistence of health and socioeconomic inequities in this ethnic group. Moreover, the vaccines failed to prevent transmission, possibly due to mutated VOCs, but they may have protected this group against severe symptoms and extended the transmission period.

Decade-Long Sustained Cellular Immunity Induced by Sequential and Repeated Vaccination with Four Heterologous HIV Vaccines in Rhesus Macaques

BACKGROUND/OBJECTIVES

Developing durable cellular immunity remains a critical challenge for HIV vaccine development.

METHODS

We evaluated a sequential and repeated heterologous prime-boost vaccination regimen using four distinct vector-based vaccines (DNA, rAd5, rSeV, and rMVA) expressing HIV-1 gag in rhesus macaques over a decade-long observation period.

RESULTS

Compared to the two-vector and control groups, the four-vector regimen elicited potent gag-specific cellular immune responses, as evidenced by IFN-γ ELISPOT assays showing sustained responses exceeding 500 SFCs/106 PBMCs for up to 52 or 69 weeks post-vaccination. Intracellular cytokine staining revealed multifunctional CD4+ and CD8+ T-cell responses, while humoral immunity against Ad5 vectors remained manageable despite repeated administrations.

CONCLUSIONS

These findings demonstrate that sequential and repeated heterologous vaccination effectively induces and maintains durable cellular immunity, providing a strategic framework for HIV vaccine design.

The immunogenicity, reactogenicity, and safety of a bivalent mRNA or protein COVID-19 vaccine given as a fourth dose

OBJECTIVES

We conducted a randomised controlled trial (RCT) to compare immunogenicity, reactogenicity and safety one month after a fourth COVID-19 mRNA or protein vaccine dose.

METHODS

This RCT recruited healthy adults in Melbourne, Australia, who had previously received three COVID-19 vaccine doses at least six months prior and had no SARS-CoV-2 infection in the last three months. The participants were randomised (1:1) to receive the bivalent mRNA vaccine (mRNA-1273.214/mRNA-1273.222, hereafter Moderna) or protein vaccine (NVX-CoV-2373, hereafter Novavax) as a fourth dose. A self-selected control group who elected not to receive an additional dose were also included. The co-primary endpoints compared immunogenicity at 28 days post-vaccination measured as binding antibodies (IgG against Ancestral and Omicron subvariants; BA.1, BA.4/5 and JN.1) between the two vaccine groups, and reactogenicity within one-week post-vaccination.

CLINICALTRIALS

gov Identifier: NCT05543356.

RESULTS

Between Feb 28 and Oct 4, 2023, 496 participants were enrolled into the study. Participants were randomised into either the bivalent mRNA Moderna (n=177) or protein Novavax (n=176) vaccine groups, with n=143 allocated to the control group. The geometric mean ratio (GMR) of anti-Spike binding IgG antibody levels were higher for the Moderna vaccine compared to the Novavax vaccine at 28 days post-vaccination for all variants tested, including Ancestral (GMR: 2.11, 95% CI: 1.88 - 2.37), BA.1 (GMR: 2.32, 95% CI 2.04 - 2.63), BA.4/5 (GMR: 2.32, 95% CI: 2.04 - 2.65), and JN.1 (GMR: 2.40, 95% CI: 2.14 - 2.70). The frequency of any local and systemic reactions (grades 1-4) was higher for the Moderna vaccine (159/177; 89.8%) compared to the Novavax vaccine (130/176; 73.9%). Serious reactions (grade 3-4) between the groups were similar (11/177; 6.2%, versus 9/176; 5.1%, respectively).

CONCLUSION

At day 28 post-vaccination, higher immunogenicity was observed following Moderna vaccination compared to Novavax vaccination when given as a fourth dose in healthy adults for Ancestral and Omicron subvariants, including JN.1. However, local and systemic reactogenicity was higher in the Moderna vaccine group compared with the Novavax vaccine group. These results may have important implications for ongoing booster strategies.

Waning neutralizing antibodies through 180 days after homologous and heterologous boosters of inactivated COVID-19 vaccine

To enhance the personal immunity to COVID-19, a third booster dose of inactivated COVID-19 vaccines program campaign was implemented in China. Our study endeavored to compare the dynamics of neutralizing antibodies generated by four distinct booster vaccines against three kinds of live SARS-CoV-2 virus (wild-type, Delta AY.23, and Omicron BA5.2). This cohort study involved 320 healthy individuals, who were randomly assigned to four groups, to receive boosters with inactivated vaccine (COVac and BIBP), the adenovirus type-5-vectored vaccine (Convidecia), and the recombinant protein-based vaccine (Zifivax), respectively, all the vaccines studied had the Wuhan variant as their parental variant. Participants were recruited from December 2021 to June 2022, with a follow-up period of 180 days. We evaluated humoral immune responses and their longevity by measuring the geometric mean titers (GMTs) of neutralizing antibodies against the SARS-CoV-2 virus at various time points post-boost. After 180 days of follow-up, 310 participants completed the study. Across all booster groups, neutralizing antibodies against the wild-type virus declined sharply within the first 90 days, accounting for an 81.24 to 92.34% reduction, then slowed down with gradually decreasing decay rates. By day 14 of post-boost, the ability to neutralize the Delta variant slightly diminished compared to the wild-type, whereas neutralizing antibodies against the Omicron variant exhibited a more pronounced decline, ranging from 10.78 to 19.88 times lower than those against the wild-type. Notably, heterologous boosting with the Convidecia vaccine maintained higher GMTs of neutralizing antibodies against both Delta and Omicron variants compared to the other boosters. At 180 days of post-boost, GMTs of neutralizing antibodies against SARS-CoV-2 had substantially decreased, yet individuals who received the Convidecia vaccine still exhibited higher titers than those who received other boosters. In summary, neutralizing antibody levels significantly waned 180 days after the third vaccine dose, with the most pronounced decline occurring within the initial 90 days. Heterologous boosting with Convidecia demonstrated a more robust, durable, and broad humoral immune response compared to boosting with inactivated vaccines or Zifivax, suggesting that adenovirus vector vaccines possess a special advantage in the realm of vaccine development for preventing infectious diseases.

COVID-19 Vaccine Booster Dose Fails to Enhance Antibody Response to Omicron Variant in Reinfected Healthcare Workers

The emergence of new variants and diverse vaccination regimens have raised uncertainty about vaccine effectiveness against SARS-CoV-2. This study aims to investigate the impact of Omicron primo-/reinfection and primary vaccination schedules on the immunogenicity of an mRNA-based booster dose over a six-month period. We conducted a prospective cohort study to assess the durability and level of antibodies of 678 healthcare workers fully vaccinated against COVID-19. They were categorized based on their primary vaccination regimen. Blood samples were collected before the booster dose and 1 and 6 months after. Significant Anti-S-RBD differences were found between previously infected and naïve volunteers (p = 0.01). Considering the initial vaccine schedules, mRNA-based vaccines displayed significant higher antibody production and longer persistence among both infected and naïve participants. After the booster dose, participants primoinfected with the Omicron variant exhibited higher antibody concentrations than those who experienced reinfection, even after 6 months of follow-up (22,545 and 9460 U/mL, respectively). Moreover, these groups showed the most pronounced disparity in antibody titers ratios between infected and uninfected individuals. Overall, the booster dose failed to enhance humoral response in individuals reinfected with the Omicron variant after receiving it. Hybrid immunity and mRNA-based vaccine initial schedules showed higher levels and longer persistence of antibodies.

Prevalence Estimation Methods for Time-Dependent Antibody Kinetics of Infected and Vaccinated Individuals: A Markov Chain Approach

Immune events such as infection, vaccination, and a combination of the two result in distinct time-dependent antibody responses in affected individuals. These responses and event prevalence combine non-trivially to govern antibody levels sampled from a population. Time-dependence and disease prevalence pose considerable modeling challenges that need to be addressed to provide a rigorous mathematical underpinning of the underlying biology. We propose a time-inhomogeneous Markov chain model for event-to-event transitions coupled with a probabilistic framework for antibody kinetics and demonstrate its use in a setting in which individuals can be infected or vaccinated but not both. We conduct prevalence estimation via transition probability matrices using synthetic data. This approach is ideal to model sequences of infections and vaccinations, or personal trajectories in a population, making it an important first step towards a mathematical characterization of reinfection, vaccination boosting, and cross-events of infection after vaccination or vice versa.

Variant-specific neutralising antibodies levels induced by the PHH-1 V SARS-CoV-2 vaccine (Bimervax®) by HIPRA

SARS-CoV-2 virus variants continue to emerge at an alarming rate due to spontaneous genetic mutations, particularly in the spike protein receptor-binding domain (RBD) portion, which render the virus more likely to escape immunity. So far, the immunity obtained through global primary and/or booster immunisation campaigns has been sufficient to protect the population from new emerging variants of the Omicron lineage. The current approach to update vaccines' antigen composition to new variants to boost immunity may not be sustainable in the long term. It might also be potentially redundant if the mutations are giving rise to variants which induce milder infections and existing vaccines, such as Bimervax®, are still sufficiently protective, as Covid is slowly becoming a seasonal illness. Through measuring neutralising antibody titres in sera from subjects boosted with Bimervax®, we have demonstrated the ability of Bimervax® to induce immune responses against a variety of SARS-CoV-2 variants, ranging from earlier variants inducing more serious infections to more recent variants which have been found to produce milder infections.

The Potential of mRNA Vaccines to Fight Against Viruses

Vaccines have always been a critical tool in preventing infectious diseases. However, the development of traditional vaccines often takes a long time and may struggle to address the challenge of rapidly mutating viruses. The emergence of mRNA technology has brought revolutionary changes to vaccine development, particularly in rapidly responding to the threat of emerging viruses. The global promotion of mRNA vaccines against severe acute respiratory syndrome coronavirus 2 has demonstrated the importance of mRNA technology. Also, mRNA vaccines targeting viruses such as influenza, respiratory syncytial virus, and Ebola are under development. These vaccines have shown promising preventive effects and safety profiles in clinical trials, although the duration of immune protection is still under evaluation. However, the development of mRNA vaccines also faces many challenges, such as stability, efficacy, and individual differences in immune response. Researchers adopt various strategies to address these challenges. Anyway, mRNA vaccines have shown enormous potential in combating viral diseases. With further development and technological maturity, mRNA vaccines are expected to have a profound impact on public health and vaccine equity. This review discussed the potential of mRNA vaccines to fight against viruses, current progress in clinical trials, challenges faced, and future prospects, providing a comprehensive scientific basis and reference for future research.

Immunogenicity, reactogenicity, and safety of a second booster with BNT162b2 or full-dose mRNA-1273: A randomized VACCELERATE trial in adults aged ≥75 years (EU-COVAT-1-AGED Part B)

OBJECTIVES

To assess the safety and immunogenicity of a fourth vaccination (second booster) in individuals aged ≥75 years.

METHODS

Participants were randomized to BNT162b2 (Comirnaty, 30 µg) or messenger RNA (mRNA)-1273 (Spikevax, 100 µg). The primary end point was the rate of two-fold antibody titer increase 14 days after vaccination, targeting the receptor binding domain (RBD) region of wild-type SARS-CoV-2. The secondary end points included changes in neutralizing activity against wild-type and 25 variants. Safety was assessed by monitoring solicited adverse events (AEs) for 7 days.

RESULTS

A total of 269 participants (mean age 81 years, mRNA-1273 n = 135/BNT162b2 n = 134) were included. Two-fold anti-RBD immunoglobulin (Ig) G titer increase was achieved by 101 of 129 (78%) and 116 of 133 (87%) subjects in the BNT162b2 and the mRNA-1273 group, respectively (P = 0.054). A second booster of mRNA-1273 provided higher anti-RBD IgG geometric mean titer: 21.326 IU/mL (95% confidence interval: 18.235-24.940) vs BNT162b2: 15.181 IU/mL (95% confidence interval: 13.172-17.497). A higher neutralizing activity was noted for the mRNA-1273 group. The most frequent AE was pain at the injection site (51% in mRNA-1273 and 48% in BNT162b2). Participants in the mRNA-1273 group had less vaccine-related AEs (30% vs 39%).

CONCLUSIONS

A second booster of either BNT162b2 or mRNA-1273 provided substantial IgG increase. Full-dose mRNA-1273 provided higher IgG levels and neutralizing capacity against SARS-CoV-2, with similar safety profile for subjects of advanced age.

Heterologous Ad26.COV2.S booster after primary BBIBP-CorV vaccination against SARS-CoV-2 infection: 1-year follow-up of a phase 1/2 open-label trial

BACKGROUND

Inactivated whole-virus vaccination elicits immune responses to both SARS-CoV-2 nucleocapsid (N) and spike (S) proteins, like natural infections. A heterologous Ad26.COV2.S booster given at two different intervals after primary BBIBP-CorV vaccination was safe and immunogenic at days 28 and 84, with higher immune responses observed after the longer pre-boost interval. We describe booster-specific and hybrid immune responses over 1 year.

METHODS

This open-label phase 1/2 study was conducted in healthy Thai adults aged ≥ 18 years who had completed primary BBIBP-CorV primary vaccination between 90-240 (Arm A1; n = 361) or 45-75 days (Arm A2; n = 104) before enrolment. All received an Ad26.COV2.S booster. We measured anti-S and anti-N IgG antibodies by Elecsys®, neutralizing antibodies by SARS-CoV-2 pseudovirus neutralization assay, and T-cell responses by quantitative interferon (IFN)-γ release assay. Immune responses were evaluated in the baseline-seronegative population (pre-booster anti-N < 1.4 U/mL; n = 241) that included the booster-effect subgroup (anti-N < 1.4 U/mL at each visit) and the hybrid-immunity subgroup (anti-N ≥ 1.4 U/mL and/or SARS-CoV-2 infection, irrespective of receiving non-study COVID-19 boosters).

RESULTS

In Arm A1 of the booster-effect subgroup, anti-S GMCs were 131-fold higher than baseline at day 336; neutralizing responses against ancestral SARS-CoV-2 were 5-fold higher than baseline at day 168; 4-fold against Omicron BA.2 at day 84. IFN-γ remained approximately 4-fold higher than baseline at days 168 and 336 in 18-59-year-olds. Booster-specific responses trended lower in Arm A2. In the hybrid-immunity subgroup at day 336, anti-S GMCs in A1 were 517-fold higher than baseline; neutralizing responses against ancestral SARS-CoV-2 and Omicron BA.2 were 28- and 31-fold higher, respectively, and IFN-γ was approximately 14-fold higher in 18-59-year-olds at day 336. Durable immune responses trended lower in ≥ 60-year-olds.

CONCLUSION

A heterologous Ad26.COV2.S booster after primary BBIBP-CorV vaccination induced booster-specific immune responses detectable up to 1 year that were higher in participants with hybrid immunity.

CLINICAL TRIALS REGISTRATION

NCT05109559.

Equal Maintenance of Anti-SARS-CoV-2 Antibody Levels Induced by Heterologous and Homologous Regimens of the BNT162b2, ChAdOx1, CoronaVac and Ad26.COV2.S Vaccines: A Longitudinal Study Up to the 4th Dose of Booster

Several technological approaches have been used to develop vaccines against COVID-19, including those based on inactivated viruses, viral vectors, and mRNA. This study aimed to monitor the maintenance of anti-SARS-CoV-2 antibodies in individuals from Brazil according to the primary vaccination regimen, as follows: BNT162b2 (group 1; 22) and ChAdOx1 (group 2; 18). Everyone received BNT162b2 in the first booster while in the second booster CoronaVac, Ad26.COV2.S, or BNT162b2. Blood samples were collected from 2021 to 2023 to analyze specific RBD (ELISA) and neutralizing antibodies (PRNT50). We observed a progressive increase in anti-RBD and neutralizing antibodies in each subsequent dose, remaining at high titers until the end of follow-up. Group 1 had higher anti-RBD antibody titers than group 2 after beginning the primary regimen, with significant differences after the 2nd and 3rd doses. Group 2 showed a more expressive increase after the first booster with BNT162B2 (heterologous booster). Group 2 also presented high levels of neutralizing antibodies against the Gamma and Delta variants until five months after the second booster. In conclusion, the circulating levels of anti-RBD and neutralizing antibodies against the two variants of SARS-CoV-2 were durable even five months after the 4th dose, suggesting that periodic booster vaccinations (homologous or heterologous) induced long-lasting immunity.

Risk Factors for Impaired Cellular or Humoral Immunity after Three Doses of SARS-CoV-2 Vaccine in Healthy and Immunocompromised Individuals

Background: We aimed to identify the risk factors for impaired cellular and humoral immunity after three doses of the SARS-CoV-2 vaccine. Methods: Six months after the third vaccine dose, T-cell immunity was evaluated using interferon-gamma release assays (IGRAs) in 60 healthy and 139 immunocompromised (IC) individuals, including patients with hematologic malignancy (HM), solid malignancy (SM), rheumatic disease (RD), and kidney transplantation (KT). Neutralizing antibody titers were measured using the plaque reduction neutralization test (PRNT) and surrogate virus neutralization test (sVNT). Results: T-cell immunity results showed that the percentages of IGRA-positive results using wild-type/alpha spike protein (SP) and beta/gamma SP were 85% (51/60) and 75% (45/60), respectively, in healthy individuals and 45.6% (62/136) and 40.4% (55/136), respectively, in IC individuals. IC with SM or KT showed a high percentage of IGRA-negative results. The underlying disease poses a risk for impaired cellular immune response to wild-type SP. The risk was low when all doses were administered as mRNA vaccines. The risk factors for an impaired cellular immune response to beta/gamma SP were underlying disease and monocyte%. In the sVNT using wild-type SP, 12 of 191 (6.3%) individuals tested negative. In the PRNT of 46 random samples, 6 (13%) individuals tested negative for the wild-type virus, and 19 (41.3%) tested negative with omicrons. KT poses a risk for an impaired humoral immune response. Conclusions: Underlying disease poses a risk for impaired cellular immune response after the third dose of the SARS-CoV-2 vaccine; KT poses a risk for impaired humoral immune response, emphasizing the requirement of precautions in patients.

Monitoring of adaptive immune responses in healthcare workers who received a Coronavirus disease 2019 vaccine booster dose

Background and Aims

Coronavirus disease 2019 (COVID-19) has become a global pandemic and led to increased mortality and morbidity. Vaccines against the etiologic agent; severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) were approved for emergency use on different platforms. In the early phase of the pandemic, Thai healthcare workers (HCWs) received CoronaVac, an inactivated vaccine, as the first vaccine against SARS-CoV-2, followed by ChAdOx1 nCoV-19, a viral vector-based vaccine, or BNT162b2, an mRNA vaccine, as a booster dose. This preliminary study evaluated the immunogenicity of ChAdOx1 nCoV-19 and BNT162b2 as a booster dose in HCWs who previously received two doses of CoronaVac.

Methods

Ten HCW participants received ChAdOx1 nCoV-19 and another 10 HCWs received BNT162b2 as a booster dose after two doses of CoronaVac. Anti-RBD IgG, neutralizing antibodies (NAb), and cellular immunity, including interferon-gamma (IFN-γ)-releasing CD4, CD8, double negative T cells, and NK cells, were measured at 3 and 5 months after the booster dose.

Results

There was no significant difference in anti-RBD IgG levels at 3 and 5 months between the two different types of booster vaccine. The levels of anti-RBD IgG and NAb were significantly decreased at 5 months. HCWs receiving BNT162b2 had significantly higher NAb levels than those receiving ChAdOx1 nCoV-19 at 5 months after the booster dose. IFN-γ release from CD4 T cells was detected at 3 months with no significant difference between the two types of booster vaccines. However, IFN-γ-releasing CD4 T cells were present at 5 months in the ChAdOx1 nCoV-19 group only.

Conclusion

ChAdOx1 nCoV-19 or BNT162b2 can be used as a booster dose after completion of the primary series primed by inactivated vaccine. Although the levels of immunity decline at 5 months, they may be adequate during the first 3 months after the booster dose.

Longitudinal immune kinetics of COVID-19 booster versus primary series vaccination: Insight into the annual vaccination strategy

Background

Data on the durability of booster dose immunity of COVID-19 vaccines are relatively limited.

Methods

Immunogenicity was evaluated for up to 9-12 months after the third dose of vaccination in 94 healthy adults.

Results

Following the third dose, the anti-spike immunoglobulin G (IgG) antibody response against the wild-type was boosted markedly, which decreased gradually over time. However, even 9-12 months after the booster dose, both the median and geometric mean of anti-spike IgG antibody levels were higher than those measured 4 weeks after the second dose. Breakthrough infection during the Omicron-dominant period boosted neutralizing antibody titers against Omicron sublineages (BA.1 and BA.5) and the ancestral strain. T-cell immune response was efficiently induced and maintained during the study period.

Conclusions

mRNA vaccine booster dose elicited durable humoral immunity for up to 1 year after the third dose and T-cell immunity was sustained during the study period, supporting an annual COVID-19 vaccination strategy.

Effectiveness of BNT162b2 mRNA vaccine third doses and previous infection in protecting against SARS-CoV-2 infections during the Delta and Omicron variant waves; the UK SIREN cohort study September 2021 to February 2022

Third doses of COVID-19 vaccines were widely deployed following the primary vaccine course waning and the emergence of the Omicron-variant. We investigated protection from third-dose vaccines and previous infection against SARS-CoV-2 infection during Delta-variant and Omicron-variant (BA.1 & BA.2) waves in our frequently PCR-tested cohort of healthcare-workers. Relative effectiveness of BNT162b2 third doses and infection-acquired immunity was assessed by comparing the time to PCR-confirmed infection in boosted participants with those with waned dose-2 protection (≥254 days after dose-2), by primary series vaccination type. Follow-up time was divided by dominant circulating variant: Delta 07 September 2021 to 30 November 2021, Omicron 13 December 2021t o 28 February 2022. We used a Cox regression model with adjustment/stratification for demographic characteristics and staff-type. We explored protection associated with vaccination, infection and both. We included 19,614 participants, 29% previously infected. There were 278 primary infections (4 per 10,000 person-days of follow-up) and 85 reinfections (0.8/10,000 person-days) during the Delta period and 2467 primary infections (43/10,000 person-days) and 881 reinfections (33/10,000) during the Omicron period. Relative Vaccine Effectiveness (VE) 0-2 months post-3rd dose (3rd dose) (3-doses BNT162b2) in the previously uninfected cohort against Delta infections was 63% (95% Confidence Interval (CI) 40%-77%) and was lower (35%) against Omicron infection (95% CI 21%-47%). The relative VE of 3rd dose (heterologous BNT162b2) was greater for primary course ChAdOX1 recipients, with VE 0-2 months post-3rd dose over ≥68% higher for both variants. Third-dose protection waned rapidly against Omicron, with no significant difference between two and three BNT162b2 doses observed after 4-months. Previous infection continued to provide additional protection against Omicron (67% (CI 56%-75%) 3-6 months post-infection), but this waned to about 25% after 9-months, approximately three times lower than against Delta. Infection rates surged with Omicron emergence. Third doses of BNT162b2 vaccine provided short-term protection, with rapid waning against Omicron infections. Protection associated with infections incurred before Omicron was markedly diminished against the Omicron wave. Our findings demonstrate the complexity of an evolving pandemic with the potential emergence of immune-escape variants and the importance of continued monitoring.

Effect of second booster vaccinations and prior infection against SARS-CoV-2 in the UK SIREN healthcare worker cohort

Background

The protection of fourth dose mRNA vaccination against SARS-CoV-2 is relevant to current global policy decisions regarding ongoing booster roll-out. We aimed to estimate the effect of fourth dose vaccination, prior infection, and duration of PCR positivity in a highly-vaccinated and largely prior-COVID-19 infected cohort of UK healthcare workers.

Methods

Participants underwent fortnightly PCR and regular antibody testing for SARS-CoV-2 and completed symptoms questionnaires. A multi-state model was used to estimate vaccine effectiveness (VE) against infection from a fourth dose compared to a waned third dose, with protection from prior infection and duration of PCR positivity jointly estimated.

Findings

1298 infections were detected among 9560 individuals under active follow-up between September 2022 and March 2023. Compared to a waned third dose, fourth dose VE was 13.1% (95% CI 0.9 to 23.8) overall; 24.0% (95% CI 8.5 to 36.8) in the first 2 months post-vaccination, reducing to 10.3% (95% CI -11.4 to 27.8) and 1.7% (95% CI -17.0 to 17.4) at 2-4 and 4-6 months, respectively. Relative to an infection >2 years ago and controlling for vaccination, 63.6% (95% CI 46.9 to 75.0) and 29.1% (95% CI 3.8 to 43.1) greater protection against infection was estimated for an infection within the past 0-6, and 6-12 months, respectively. A fourth dose was associated with greater protection against asymptomatic infection than symptomatic infection, whilst prior infection independently provided more protection against symptomatic infection, particularly if the infection had occurred within the previous 6 months. Duration of PCR positivity was significantly lower for asymptomatic compared to symptomatic infection.

Interpretation

Despite rapid waning of protection, vaccine boosters remain an important tool in responding to the dynamic COVID-19 landscape; boosting population immunity in advance of periods of anticipated pressure, such as surging infection rates or emerging variants of concern.

Funding

UK Health Security Agency, Medical Research Council, NIHR HPRU Oxford, Bristol, and others.

One-year antibody durability induced by EuCorVac-19, a liposome-displayed COVID-19 receptor binding domain subunit vaccine, in healthy Korean subjects

OBJECTIVE

EuCorVac-19 (ECV-19), an adjuvanted liposome-displayed receptor binding domain (RBD) COVID-19 vaccine, previously reported interim Phase 2 trial results showing induction of neutralizing antibodies 3 weeks after prime-boost immunization. The objective of this study was to determine the longer-term antibody response of the vaccine.

METHODS

To assess immunogenicity 6 and 12 months after vaccination, participants in the Phase 2 trial (NCT04783311) were excluded if they: 1) withdrew, 2) reported COVID-19 infection or additional vaccination, or 3) exhibited increasing Spike (S) antibodies (representing possible non-reported infection). Following exclusions, of the 197 initial subjects, anti-S IgG antibodies and neutralizing antibodies were further assessed in 124 subjects at the 6-month timepoint, and 36 subjects at the 12-month timepoint.

RESULTS

Median anti-S antibody half-life was 52 days (interquartile range [IQR]:42-70), in the "early" period from 3 weeks to 6 months, and 130 days (IQR:97-169) in the "late" period from 6 to 12 months. There was a negative correlation between initial antibody titer and half-life. Anti-S and neutralizing antibody responses were correlated. Neutralizing antibody responses showed longer half-lives; the early period had a median half-life of 120 days (IQR:81-207), and the late period had a median half-life of 214 days (IQR:140-550).

CONCLUSION

These data establish antibody durability of ECV-19, using a framework to analyze COVID-19 vaccine-induced antibodies during periods of high infection.

Pivoting to protein: the immunogenicity and safety of protein-based NVX-CoV2373 as a heterologous booster for inactivated and viral vector COVID-19 vaccines

INTRODUCTION

Approximately half of the 13.4 billion COVID-19 vaccine doses administered globally were inactivated or viral vector platforms. The harmonization and optimization of vaccine regimens has become a key focus of policymakers and health-care providers and presents an opportunity to reassess the continued use of pandemic-era vaccines.

AREAS COVERED

Immunological evidence from studies of various homologous and heterologous regimens has been rapidly published; however, interpretation of these data is complicated by the many vaccine types and highly variable participant viral exposure and vaccination histories. Recent studies demonstrate that after primary series doses of inactivated (i.e. BBV152, and BBIBP-CorV), and viral vector (ChAdOx1 nCov-2019) vaccines, a heterologous boost with protein-based NVX-CoV2373 elicits more potent ancestral strain and omicron-specific antibody responses compared to homologous and heterologous inactivated and viral vector boosts.

EXPERT OPINION

While mRNA vaccines likely yield similar performance to protein-based heterologous booster doses, the latter offers notable advantages to countries with high uptake of inactivated and viral vector vaccines in terms of transportation and storage logistics and can potentially appeal to vaccine hesitant individuals. Moving forward, vaccine-mediated protection in inactivated and viral vector recipients may be optimized with the use of a heterologous protein-based booster such as NVX-CoV2373.

PIVOTING TO PROTEIN

The Immunogenicity and Safety of Protein-based NVX-CoV2373 as a Heterologous Booster for Inactivated and Viral Vector COVID-19 Vaccines. Inactivated or viral vector primary series following a booster dose with homologous or heterologous inactivated vaccines (i.e., BBV152, BBIBP-CorV), and homologous or heterologous viral vector vaccines (i.e., ChAd-Ox1 nCov-19) induces suboptimal immunogenicity compared to the enhanced immunogenicity of heterologous protein-based vaccine NVX-CoV2373.

Safety, immunogenicity and immune-persistence of heterologous prime-boost immunization with BBIBP-CorV and ZF2001 against SARS-CoV-2 in healthy adults aged 18 years or older

BACKGROUND

Because SARS-CoV-2 mutations and immunity wane over time, a third dose of heterologous COVID-19 vaccine is proposed for individuals primed with inactivated COVID-19 vaccine.

RESEARCH DESIGN AND METHODS

We conducted a single-center, open-label trial to assess the safety, immunogenicity, and immune-persistence of a heterologous BBIBP-CorV/ZF2001 prime-boost vaccination in Chinese adults. 480 participants who had been primed with two doses of BBIBP-CorV, received a third dose of ZF2001 after an interval of 3-4, 5-6, or 7-9 months.

RESULTS

The overall incidence of adverse reactions within 30 days after vaccination was 5.83%. No serious adverse reactions were reported. The respective geometric mean titers (GMTs) of neutralizing antibodies for 3-4, 5-6, and 7-9 months groups at baseline were 2.06, 2.02, and 2.10; which increased to 55.42, 63.45, and 62.06 on day 14; then decreased to 17.53, 23.79, and 26.73 on day 30; before finally waning to 8.29, 9.24, and 9.51 on day 180. After the booster, the three groups showed no significant differences in GMTs. GMTs were lower in older participants than younger participants.

CONCLUSIONS

A heterologous BBIBP-CorV/ZF2001 prime-boost vaccination was safe and immunogenic. Prime-boost intervals did not affect the immune response. The immune response was weaker in older adults than younger adults.

CLINICAL TRIAL IDENTIFIER

NCT05205083.