Heterologous immunization with inactivated vaccine followed by mRNA-booster elicits strong immunity against SARS-CoV-2 Omicron variant

Preliminary evaluation of a novel serotype O foot-and-mouth disease mRNA vaccine

Foot-and-mouth disease virus (FMDV) is one of the most significant animal pathogens worldwide, severely impacting the health and productivity of pigs, cattle, sheep, and other ungulates. Although the traditional vaccines have played a crucial role in epidemic control, inactivated vaccines face persistent challenges concerning the potential for virus dissemination and pressures from serotype and subtype matching. However, the manufacture of attenuated vaccines is forbidden, and the efficiency of alternative vaccines for immune protection is still inadequate. Consequently, there exists an urgent need for safer and more effective innovative vaccines in animal husbandry. In this study, we aimed to develop a lipid nanoparticle mRNA vaccine based on VP1-3A-3D epitopes from serotype O FMD and to verify its specific expression within cytoplasmic and injection sites. Our findings demonstrated that mRNA transfected into primary spleen cells derived from guinea pigs induced cytokine release, promoted differentiation of both CD4+ T and CD8+ T lymphocytes, and enhanced lymphocyte proliferation rates. Following immunization of mRNA vaccine in guinea pigs, we observed increased differentiation of both CD4+ T and CD8+ T cells, alongside elevated levels of cytokine secretion. Additionally, this vaccination induced the production of specific IgG antibodies as well as neutralizing antibodies. Importantly, our vaccine provided complete protection for all six guinea pigs against a lethal challenge of 100 GPID50, with histopathological scores indicating protection equivalent to that conferred by the inactivated vaccine. The viral load results demonstrated that the vaccine group significantly reduced viral copy numbers in serum and effectively decreased the concentration of the inflammatory cytokine IL-1β. Furthermore, during the pre-immune phase following vaccination with the mRNA vaccine in pigs, heightened cytokine secretion was observed, along with the inhibition of viral replication. Simultaneously, the neutralizing antibody titer in the serum remained stable over 4 months. Immunofluorescence analysis of spleen tissues from both guinea pigs and pigs demonstrated marked activation and increased expression of CD4+ and CD8+ T lymphocytes, as well as macrophages, in the mRNA vaccine group. In summary, this study suggests that the serotype O FMD mRNA vaccine is a promising candidate for further development in the fight against FMDV.

Effect of heterologous intranasal iNCOVACC® vaccination as a booster to two-dose intramuscular Covid-19 vaccination series: a randomized phase 3 clinical trial

BACKGROUND

Due to waning immunity and emerging variants, protection following primary intramuscular Covid-19 vaccinations is decreasing, so health agencies have been proposing heterologous booster vaccinations. Here, we report immunogenicity and safety evaluation of heterologous booster vaccination with an intranasal, adenovirus vectored SARS-CoV-2 vaccine (BBV154) in healthy adults, who were previously primed with two doses of either Covaxin® or Covishield™. We compare results with use of a homologous booster vaccination combination.

METHODS

This was a randomized, open-label phase 3 trial conducted to evaluate immunogenicity and safety of a booster dose of intranasal BBV154 vaccine or intramuscular EUA approved Covid-19 vacines in India. Healthy participants of ≥18 years age with no history of SARS-CoV-2 infection, who received two doses of Covaxin® or Covishield™ at least 6 ± 1 months earlier were enrolled. The primary outcome was the neutralising antibody titers against wild-type virus using a plaque-reduction neutralization test (PRNT50). Other outcomes measured were humoral (IgG), mucosal (IgA) and cell mediated responses. The protocol was registered #NCT05567471 and approved by National Regulatory Authority (India) #CTRI/2022/02/039992.

RESULTS

In this phase 3 trial, a total of 875 participants were randomized into 5 Groups in a ratio of 2:1:2:1:1 to receive either booster dose of BBV154 or Covaxin or Covishield. Based on per-protocol population, at Day 56, neutralization antibody titres were 564.1 (479·1, 664·1), 578.1 (436·9, 764·9), 655.5 (533·3, 805·8), 625.4 (474·7, 824·0), 650.1 (519·7, 813·1) for Group 1 to 5 respectively. This study was conducted, whilst the Omicron variant was prevalent. There were varying levels of severity of infection across different study sites with varied baseline antibody titers. Consequently, the average neutralization (PRNT50) antibody titers are similar across all Groups on day 56 and exhibited large differences within the Group, depending on the study site. All booster vaccinations are well tolerated and reported no serious adverse events; in particular, study participants boosted with BBV154 had significantly fewer solicited local adverse events than those primed and boosted with Covishield.

CONCLUSIONS

These findings demonstrate that impact of booster across different cohorts is governed by infection status of the individual and geographical diversity, thus necessitating large cohorts, well distributed studies before Covid-19 booster effects are interpreted.

RBD-depleted SARS-CoV-2 spike generates protective immunity in cynomolgus macaques

The SARS-CoV-2 pandemic revealed the rapid evolution of circulating strains. This led to new variants carrying mostly mutations within the receptor binding domain, which is immunodominant upon immunization and infection. In order to steer the immune response away from RBD epitopes to more conserved domains, we generated S glycoprotein trimers without RBD and stabilized them by formaldehyde cross-linking. The cryoEM structure demonstrated that SΔRBD folds into the native prefusion conformation, stabilized by one specific cross-link between S2 protomers. SΔRBD was coated onto lipid vesicles, to produce synthetic virus-like particles, SΔRBD-LV, which were utilized in a heterologous prime-boost strategy. Immunization of cynomolgus macaques either three times with the mRNA Comirnaty vaccine or two times followed by SΔRBD-LV showed that the SΔRBD-LV boost induced similar antibody titers and neutralization of different variants, including omicron. Upon challenge with omicron XBB.3, both the Comirnaty only and Comirnaty/SΔRBD-LV vaccination schemes conferred similar overall protection from infection for both the Comirnaty only and Comirnaty/SΔRBD-LV vaccination schemes. However, the SΔRBD-LV boost indicated better protection against lung infection than the Comirnaty strategy alone. Together our findings indicate that SΔRBD is highly immunogenic and provides improved protection compared to a third mRNA boost indicative of superior antibody-based protection.

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.

A promising mRNA vaccine derived from the JN.1 spike protein confers protective immunity against multiple emerged Omicron variants

Despite the declared end of the COVID-19 pandemic, SARS-CoV-2 continues to evolve, with emerging JN.1-derived subvariants (e.g., KP.2, KP.3) compromising the efficacy of current XBB.1.5-based vaccines. To address this, we developed an mRNA vaccine encoding the full-length spike protein of JN.1, incorporating GSAS and 2P mutations and encapsulated in lipid nanoparticles (LNPs). The JN.1-mRNA vaccine elicited robust humoral and cellular immune responses in mice, including high JN.1-specific IgG titers, cross-neutralizing antibodies, and increased T follicular helper (Tfh) cells, germinal center (GC) B cells, and T cell cytokines. Importantly, immunity persisted for up to six months and induced RBD-specific long-lived plasma cells. We also compared the immune responses induced by homologous and heterologous vaccination regimens, and our results demonstrated that the heterologous regimen-combining JN.1-mRNA with a recombinant protein vaccine (RBDJN.1-HR)-induced stronger responses. These findings highlight the JN.1-mRNA vaccine constitutes an effective prophylactic approach against JN.1-related variants, as it induces potent neutralizing antibody responses across all tested lineages. This enhanced immunogenicity is expected to significantly reduce hospitalization rates and mitigate post-COVID complications associated with JN.1 and KP.3 infections. This study emphasizes the need for timely vaccine updates and the adaptability of mRNA vaccines in addressing emerging pathogens, providing a framework for combating future infectious diseases. Collectively, these results offer critical insights for vaccine design and public health strategies in response to emerging SARS-CoV-2 variants.

A Meta-Analysis on the Immunogenicity of Homologous versus Heterologous Immunization Regimens against SARS-CoV-2 Beta, Delta, and Omicron BA.1 VoCs in Healthy Adults

Since the outbreak of the COVID-19 pandemic, SARS-CoV-2 has not stopped evolving, leading to the emergence of variants of concern (VoCs) involved in significant immune escape. Here, we compared the immunogenicity of different prime-boost vaccination regimens against SARS-CoV-2 wildtype (WT) and its Beta, Delta, and Omicron BA.1 VoCs. We used 5 databases to retrieve publications and random-effect models to estimate pooled neutralization titers. We included 11 randomized controlled trials (RCTs) and 16 non-RCTs, 10 prime-boost vaccination regimens, and 4598 subjects. We found neutralization activity against SARS-CoV-2 decreased with virus evolution. The heterologous immunization was more effective. The increase in neutralization titers against SARS-CoV-2 WT and Beta, Delta, and Omicron BA.1 VoCs after heterologous immunization was 1.41(95%CI:0.82-2.01), 0.90(95%CI:0.39-1.41), 1.23 (95%CI: 0.81-1.65), and 1.32 (95%CI: 0.99-1.65), respectively. Furthermore, the booster dose of viral vector vaccine did not show a higher increase in neutralization titers against SARS-CoV-2 WT(MD=0.48; 95%CI:-1.12-1.09), Beta (MD=0.20; 95%CI:-0.26-0.67), Delta (MD=0.35; 95%CI:-0.09-0.79), and Omicron BA.1 (MD=0.38; 95%CI:-0.14-0.89) VoCs. The combination of inactivated-recombinant protein vaccines showed a higher increase in neutralization titers (Beta: MD=1.88 and Delta: MD=1.70) than other combinations of vaccines. However, only a combination of mRNA-viral vector vaccines showed a higher increase in neutralization titers (MD:1.52; 95%CI:0.34-2.70) against Omicron BA.1 VoC. Interestingly, the viral vector-mRNA immunization regimen appears better compared to mRNA-viral vector regimen, especially against Beta and Delta VoCs. Overall, the type of combination followed by the order of administration of COVID-19 vaccines could be a potential vaccine strategy against the occurrence of SARS-CoV-2 variants.

Neutralizing and binding antibody dynamics following primary and booster COVID-19 vaccination among healthcare workers

BACKGROUND

Vaccine-induced neutralizing antibodies (NAbs) are key for COVID-19 protective-immunity. As the efficacy of SARS-CoV-2 vaccines declines over time and variants of the virus continue to emerge, the need for booster doses of vaccine remains on the agenda. The aim of this study was to assess NAbs dynamics and its correlation with anti-RBD IgG levels during the nine-month follow-up period after primary-CoronaVac vaccination and booster vaccinations to evaluate vaccination strategies.

METHODS

This prospective longitudinal observational study followed 226 healthcare workers who received primary (two doses CoronaVac) and booster (CoronaVac or BNT162b2) immunization. Serum samples were collected at four different time points, two after primary vaccination and two after booster. Anti-RBD IgG antibody levels were assessed with the SARS CoV-2 IgG-II-QUANT kit (Abbott, USA) and neutralizing antibody levels were determined with the ACE2-RBD-Neutralization-Assay (Dia-Pro, Italy) using a surrogate virus neutralization method. Factors affecting antibody response were analyzed. Statistical analysis was performed with IBM-SPSS-22.0.

RESULTS

One month after the second dose of CoronaVac, 79.2% of participants had NAb, but this had decreased to 49.7% by the fourth month and was influenced by smoking, BMI and chronic diseases. Boosters, regardless of type, significantly raised NAb levels. Heterologous vaccination yielded higher NAb and anti-RBD IgG responses. Both single or double-BNT162b2 boosters resulted in similar NAb responses. There was a strong correlation between anti-RBD IgG and NAb levels following CoronaVac vaccination, leading to the identification of predictive IgG threshold for the presence of NAb. The type of booster influenced the correlation strength and threshold-value.

CONCLUSIONS

NAbs levels decreased rapidly after primary CoronaVac vaccination. Boosters significantly increased levels while the heterologous vaccine combination induced a greater response. Anti-RBD IgG levels were able to predict the NAb response, however the correlation varied by the vaccine type, NAb response strength and the time since vaccination.

An allelic atlas of immunoglobulin heavy chain variable regions reveals antibody binding epitope preference resilient to SARS-CoV-2 mutation escape

Background

Although immunoglobulin (Ig) alleles play a pivotal role in the antibody response to pathogens, research to understand their role in the humoral immune response is still limited.

Methods

We retrieved the germline sequences for the IGHV from the IMGT database to illustrate the amino acid polymorphism present within germline sequences of IGHV genes. We aassembled the sequences of IgM and IgD repertoire from 130 people to investigate the genetic variations in the population. A dataset comprising 10,643 SARS-CoV-2 spike-specific antibodies, obtained from COV-AbDab, was compiled to assess the impact of SARS-CoV-2 infection on allelic gene utilization. Binding affinity and neutralizing activity were determined using bio-layer interferometry and pseudovirus neutralization assays. Primary docking was performed using ZDOCK (3.0.2) to generate the initial conformation of the antigen-antibody complex, followed by simulations of the complete conformations using Rosetta SnugDock software. The original and simulated structural conformations were visualized and presented using ChimeraX (v1.5).

Results

We present an allelic atlas of immunoglobulin heavy chain (IgH) variable regions, illustrating the diversity of allelic variants across 33 IGHV family germline sequences by sequencing the IgH repertoire of in the population. Our comprehensive analysis of SARS-CoV-2 spike-specific antibodies revealed the preferential use of specific Ig alleles among these antibodies. We observed an association between Ig alleles and antibody binding epitopes. Different allelic genotypes binding to the same RBD epitope on the spike show different neutralizing potency and breadth. We found that antibodies carrying the IGHV1-69*02 allele tended to bind to the RBD E2.2 epitope. The antibodies carrying G50 and L55 amino acid residues exhibit potential enhancements in binding affinity and neutralizing potency to SARS-CoV-2 variants containing the L452R mutation on RBD, whereas R50 and F55 amino acid residues tend to have reduced binding affinity and neutralizing potency. IGHV2-5*02 antibodies using the D56 allele bind to the RBD D2 epitope with greater binding and neutralizing potency due to the interaction between D56 on HCDR2 and K444 on RBD of most Omicron subvariants. In contrast, IGHV2-5*01 antibodies using the N56 allele show increased binding resistance to the K444T mutation on RBD.

Discussion

This study provides valuable insights into humoral immune responses from the perspective of Ig alleles and population genetics. These findings underscore the importance of Ig alleles in vaccine design and therapeutic antibody development.

Enhanced immunity against SARS-CoV-2 in returning Chinese individuals

Global COVID-19 vaccination programs effectively contained the fast spread of SARS-CoV-2. Characterizing the immunity status of returned populations will favor understanding the achievement of herd immunity and long-term management of COVID-19 in China. Individuals were recruited from 7 quarantine stations in Guangzhou, China. Blood and throat swab specimens were collected from participants, and their immunity status was determined through competitive ELISA, microneutralization assay and enzyme-linked FluoroSpot assay. A total of 272 subjects were involved in the questionnaire survey, of whom 235 (86.4%) were returning Chinese individuals and 37 (13.6%) were foreigners. Blood and throat swab specimens were collected from 108 returning Chinese individuals. Neutralizing antibodies against SARS-CoV-2 were detected in ~90% of returning Chinese individuals, either in the primary or the homologous and heterologous booster vaccination group. The serum NAb titers were significantly decreased against SARS-CoV-2 Omicron BA.5, BF.7, BQ.1 and XBB.1 compared with the prototype virus. However, memory T-cell responses, including specific IFN-γ and IL-2 responses, were not different in either group. Smoking, alcohol consumption, SARS-CoV-2 infection, COVID-19 vaccination, and the time interval between last vaccination and sampling were independent influencing factors for NAb titers against prototype SARS-CoV-2 and variants of concern. The vaccine dose was the unique common influencing factor for Omicron subvariants. Enhanced immunity against SARS-CoV-2 was established in returning Chinese individuals who were exposed to reinfection and vaccination. Domestic residents will benefit from booster homologous or heterologous COVID-19 vaccination after reopening of China, which is also useful against breakthrough infection.

Optimizing immunogenicity and product presentation of a SARS-CoV-2 subunit vaccine composition: effects of delivery route, heterologous regimens with self-amplifying RNA vaccines, and lyophilization

Introduction

Dozens of vaccines have been approved or authorized internationally in response to the ongoing SARS-CoV-2 pandemic, covering a range of modalities and routes of delivery. For example, mucosal delivery of vaccines via the intranasal (i.n.) route has been shown to improve protective mucosal responses in comparison to intramuscular (i.m.) delivery. As we gain knowledge of the limitations of existing vaccines, it is of interest to understand if changes in product presentation or combinations of multiple vaccine modalities can further improve immunological outcomes.

Methods

We investigated a commercial-stage SARS-CoV-2 receptor binding domain (RBD) antigen adjuvanted with a clinical-stage TLR-7/8 agonist (3M-052) formulated on aluminum oxyhydroxide (Alum). In a murine immunogenicity model, we compared i.n. and i.m. dosing of the RBD-3M-052-Alum vaccine. We measured the magnitude of antibody responses in serum and lungs, the antibody-secreting cell populations in bone marrow, and antigen-specific cytokine-secreting splenocyte populations. Similarly, we compared different heterologous and homologous prime-boost regimens using the RBD-3M-052-Alum vaccine and a clinical-stage self-amplifying RNA (saRNA) vaccine formulated on a nanostructured lipid carrier (NLC) using the i.m. route alone. Finally, we developed a lyophilized presentation of the RBD-3M-052-Alum vaccine and compared it to the liquid presentation and a heterologous regimen including a previously characterized lyophilized form of the saRNA-NLC vaccine.

Results and discussion

We demonstrate that i.n. dosing of the RBD-3M-052-Alum vaccine increased IgA titers in the lung by more than 1.5 logs, but induced serum IgG titers 0.8 logs lower, in comparison to i.m. dosing of the same vaccine. We also show that the homologous prime-boost RBD-3M-052-Alum regimen led to the highest serum IgG and bronchial IgA titers, whereas the homologous saRNA-NLC regimen led to the highest splenocyte interferon-γ response. We found that priming with the saRNA-NLC vaccine and boosting with the RBD-3M-052-Alum vaccine led to the most desirable immune outcome of all regimens tested. Finally, we show that the lyophilized RBD-3M-052-Alum vaccine retained its immunological characteristics. Our results demonstrate that the route of delivery and the use of heterologous regimens each separately impacts the resulting immune profile, and confirm that multi-product vaccine regimens can be developed with stabilized presentations in mind.

SpiN-Tec: A T cell-based recombinant vaccine that is safe, immunogenic, and shows high efficacy in experimental models challenged with SARS-CoV-2 variants of concern

The emergence of new SARS-CoV-2 variants of concern associated with waning immunity induced by natural infection or vaccines currently in use suggests that the COVID-19 pandemic will become endemic. Investing in new booster vaccines using different platforms is a promising way to enhance protection and keep the disease under control. Here, we evaluated the immunogenicity, efficacy, and safety of the SpiN-Tec vaccine, based on a chimeric recombinant protein (SpiN) adjuvanted with CTVad1 (MF59-based adjuvant), aiming at boosting immunity against variants of concern of SARS-CoV-2. Immunization of K18-hACE-2 transgenic mice and hamsters induced high antibody titers and cellular immune response to the SpiN protein as well as to its components, RBD and N proteins. Importantly in a heterologous prime/boost protocol with a COVID-19 vaccine approved for emergency use (ChAdOx1), SpiN-Tec enhanced the level of circulation neutralizing antibodies (nAb). In addition to protection against the Wuhan isolate, protection against the Delta and Omicron variants was also observed as shown by reduced viral load and lung pathology. Toxicity and safety tests performed in rats demonstrated that the SpiN-Tec vaccine was safe and, based on these results, the SpiN-Tec phase I/II clinical trial was approved.

The characterization of CD8+ T-cell responses in COVID-19

This review gives an overview of the protective role of CD8+ T cells in SARS-CoV-2 infection. The cross-reactive responses intermediated by CD8+ T cells in unexposed cohorts are described. Additionally, the relevance of resident CD8+ T cells in the upper and lower airway during infection and CD8+ T-cell responses following vaccination are discussed, including recent worrisome breakthrough infections and variants of concerns (VOCs). Lastly, we explain the correlation between CD8+ T cells and COVID-19 severity. This review aids in a deeper comprehension of the association between CD8+ T cells and SARS-CoV-2 and broadens a vision for future exploration.

Maintenance of Long-Term Effective Humoral Immune Response in Patients with COVID-19 with Homologous or Heterologous Booster Vaccines: A Retrospective Study

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and first identified in Wuhan, China, in December 2019, has led to global efforts in vaccination to mitigate rising morbidity and mortality, with vaccines proving crucial in controlling the pandemic. This study evaluated the humoral responses to the inactivated virus vaccine Sinopharm or Koxing Kerlafor, the protein subunit vaccine ZF001, and the adenoviral vector vaccine Convidecia after 18 months of inactivated virus vaccination by heterologous and homologous booster vaccination in patients with previous SARS-CoV-2 infection and healthy individuals. We discovered that patients who had recovered from the infection and then received a third vaccine dose (booster) exhibited durable immunity. Furthermore, the heterologous booster vaccine induced higher neutralizing antibody responses compared with the homologous booster. These findings offer valuable insights into the efficacy of different COVID-19 vaccine strategies following booster immunization.

Impact of Immunosenescence on Vaccine Immune Responses and Countermeasures

The biological progression of aging encompasses complex physiological processes. As individuals grow older, their physiological functions gradually decline, including compromised immune responses, leading to immunosenescence. Immunosenescence significantly elevates disease susceptibility and severity in older populations while concurrently compromising vaccine-induced immune responses. This comprehensive review aims to elucidate the implications of immunosenescence for vaccine-induced immunity and facilitate the development of optimized vaccination strategies for geriatric populations, with specific focus on COVID-19, influenza, pneumococcal, herpes zoster, and respiratory syncytial virus (RSV) vaccines. This review further elucidates the relationship between immunosenescence and vaccine-induced immunity. This review presents a systematic evaluation of intervention strategies designed to enhance vaccine responses in older populations, encompassing adjuvant utilization, antigen doses, vaccination frequency modification, inflammatory response modulation, and lifestyle interventions, including physical activity and nutritional modifications. These strategies are explored for their potential to improve current vaccine efficacy and inform the development of next-generation vaccines for geriatric populations.

Development of pseudotyped VSV-SARS-CoV-2 spike variants for the assessment of neutralizing antibodies

Aim: Serological studies with pseudotyped viruses offer a safer alternative to live SARS-CoV-2 in evaluating neutralizing antibodies, enabling research in standard labs.Methods: The SARS-CoV-2 Spike pseudotyped vesicular stomatitis virus (VSV) pseudoviruses were generated using Spike of Wuhan strain and two variants (B.1.1.7, B.1.351) and utilized to evaluate the serum neutralizing activity of human plasma samples of vaccinated (n = 13) and healthy people (n = 2) compared with a plaque assay with authentic virus.Results: Neutralizing titer of convalescent plasma resulted with a good correlation (R2 = 0.7).Conclusion: We evaluated a safe and reliable pseudotyped virus system that effectively mimics authentic virus and correlates well with traditional assays. The developed system allows easier testing of variants and has the potential to improve vaccine development.

Efficacy, immunogenicity, and safety of a monovalent mRNA vaccine, ABO1020, in adults: A randomized, double-blind, placebo-controlled, phase 3 trial

BACKGROUND

ABO1020 is a monovalent COVID-19 mRNA vaccine. Results from a phase 1 trial showed ABO1020 was safe and well tolerated, and phase 3 trials to evaluate the efficacy, immunogenicity, and safety of ABO1020 in healthy adults are urgently needed.

METHODS

We conducted a multinational, randomized, placebo-controlled, double-blind, phase 3 trial among healthy adults (ClinicalTrials.gov: NCT05636319). Participants were randomly assigned (1:1) to receive either 2 doses of ABO1020 (15 μg per dose) or placebo, administered 28 days apart. The primary endpoint was the vaccine efficacy in preventing symptomatic COVID-19 cases that occurred at least 14 days post-full vaccination. The second endpoint included the neutralizing antibody titers against Omicron BA.5 and XBB and safety assessments.

FINDINGS

A total of 14,138 participants were randomly assigned to receive either vaccine or placebo (7,069 participants in each group). A total of 366 symptomatic COVID-19 cases were confirmed 14 days after the second dose among 93 participants in the ABO1020 group and 273 participants in the placebo group, yielding a vaccine efficacy of 66.18% (95% confidence interval: 57.21-73.27, p < 0.0001). A single dose or two doses of ABO1020 elicited potent neutralizing antibodies against both BA.5 and XBB.1.5. The safety profile of ABO1020 was characterized by transient, mild-to-moderate fever, pain at the injection site, and headache.

CONCLUSION

ABO1020 was well tolerated and conferred 66.18% protection against symptomatic COVID-19 in adults.

FUNDING

National Key Research and Development Project of China, Innovation Fund for Medical Sciences from the CAMS, National Natural Science Foundation of China.

Hybrid Immunity against SARS-CoV-2 Variants: A Narrative Review of the Literature

The emergence of SARS-CoV-2 led to a global health crisis and the burden of the disease continues to persist. The rapid development and emergency authorization of various vaccines, including mRNA-based vaccines, played a pivotal role in mitigating severe illness and mortality. However, rapid viral mutations, leading to several variants of concern, challenged vaccine effectiveness, particularly concerning immune evasion. Research on immunity, both from natural infection and vaccination, revealed that while neutralizing antibodies provide protection against infection, their effect is short-lived. The primary defense against severe COVID-19 is derived from the cellular immune response. Hybrid immunity, developed from a combination of natural infection and vaccination, offers enhanced protection, with convalescent vaccinated individuals showing significantly higher levels of neutralizing antibodies. As SARS-CoV-2 continues to evolve, understanding the durability and breadth of hybrid immunity becomes crucial. This narrative review examines the latest data on humoral and cellular immunity from both natural infection and vaccination, discussing how hybrid immunity could inform and optimize future vaccination strategies in the ongoing battle against COVID-19 and in fear of a new pandemic.

Safety and immunogenicity of COReNAPCIN, a SARS-CoV-2 mRNA vaccine, as a fourth heterologous booster in healthy Iranian adults: A double-blind, randomized, placebo-controlled, phase 1 clinical trial with a six-month follow-up

The recurrent COVID-19 infection, despite global vaccination, highlights the need for booster doses. A heterologous booster has been suggested to enhance immunity and protection against emerging variants of concern of the SARS-CoV-2 virus. In this report, we aimed to assess the safety, and immunogenicity of COReNAPCIN, as a fourth booster dose after three doses of inactivated vaccines.

METHODS

The study was conducted as a double-blind, randomized, placebo-controlled phase 1 clinical trial of the mRNA-based vaccine candidate, COReNAPCIN. The vaccine was injected as a heterologous booster in healthy Iranian adults aged 18-50 who had previously received three doses of inactivated SARS-CoV-2 vaccines. In the study, 30 participants were randomly assigned to receive either COReNAPCIN in two different doses (25 µg and 50 µg) or placebo. The vaccine candidate contained mRNA encoding the complete sequence of the pre-fusion stabilized Spike protein of SARS-CoV-2, formulated within lipid nanoparticles. The primary endpoint was safety and the secondary objective was humoral immunogenicity until 6 months post-vaccination. The cellular immunogenicity was pursued as an exploratory outcome.

RESULTS

COReNAPCIN was well tolerated in vaccinated individuals in both doses with no life-threatening or other serious adverse events. The most noticeable solicited adverse events were pain at the site of injection, fatigue and myalgia. Regarding the immunogenicity, despite the seroprevalence of SARS-CoV-2 antibodies due to the vaccination history for all and previous SARS-CoV-2 infection for some participants, the recipients of 25 and 50 µg COReNAPCIN, two weeks post-vaccination, showed 6·6 and 8·1 fold increase in the level of anti-RBD, and 11·5 and 21·7 fold increase in the level of anti-spike antibody, respectively. The geometric mean virus neutralizing titers reached 10.2 fold in the 25 µg group and 8.4 fold in 50 µg group of pre-boost levels. After 6 months, the measured anti-spike antibody concentration still maintains a geometric mean fold rise of 2.8 and 6.3, comparing the baseline levels in 25 and 50 µg groups, respectively. Additionally, the significant increase in the spike-specific IFN-ϒ T-cell response upon vaccination underscores the activation of cellular immunity.

CONCLUSION

COReNAPCIN booster showed favorable safety, tolerability, and immunogenicity profile, supporting its further clinical development (Trial registration: IRCT20230131057293N1).

Efficacy, safety, and immunogenicity of SARS-CoV-2 mRNA vaccine (Omicron BA.5) LVRNA012: a randomized, double-blind, placebo-controlled phase 3 trial

Background

We aimed to evaluate the efficacy, safety, and immunogenicity of a SARS-CoV-2 mRNA vaccine (Omicron BA.5) LVRNA012 given as the booster in immunized but SARS-CoV-2 infection-free adults in China.

Methods

This is a single-center, randomized, double-blind, placebo-controlled phase 3 clinical trial enrolling healthy adult participants (≥18 years) who had completed two or three doses of inactivated COVID-19 vaccines at least 6 months before, in Bengbu, Anhui province, China. Eligible participants were randomly assigned (1:1) to receive a booster intramuscular vaccination with an LVRNA012 vaccine (100ug) or placebo. The primary endpoint was the protective efficacy of a booster dose of the LVRNA012 vaccine or placebo against symptomatic COVID-19 of any severity 14 days after vaccination. Laboratory-confirmed COVID-19 infections were identified from 14 days to 180 days after intervention, with active surveillance for symptomatic illness 8 times per month between 7 to 90 days and at least once per month between 90 to 180 days after intervention.

Results

2615 participants were recruited and randomly assigned in a 1:1 ratio to either the vaccine group (1308) or the placebo group (1307). A total of 141 individuals (46 in the LVRNA012 group and 95 in the placebo group) developed symptomatic COVID-19 infection 14 days after the booster immunization, showing a vaccine efficacy of 51.9% (95% CI, 31.3% to 66.4%). Most infections were detected 90 days after intervention during a period when XBB was prevalent in the community. Adverse reactions were reported by 64% of participants after the LVRNA012 vaccination, but most of them were mild or moderate. The booster vaccination with the LVRNA012 mRNA vaccine could significantly enhance neutralizing antibody titers against the Omicron variant XBB.1.5 (GMT 132.3 [99.8, 175.4]) than did those in the placebo group (GMT 12.5 [8.4, 18.7]) at day 14 for the previously immunized individuals.

Conclusion

The LVRNA012 mRNA vaccine is immunogenic, and shows robust efficacy in preventing COVID-19 during the omicron-predominate period.

Clinical trial registration

ClinicalTrials.gov, identifier NCT05745545.

Evaluation of antibody responses in healthy individuals receiving SARS-CoV-2 inactivated vaccines

Inactivated coronavirus disease 2019 (COVID-19) vaccines such as CoronaVac and BBIBP-CorV have been widely used in China. However, more investigation is still needed to understand antibodies' duration and effectiveness against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants in the real world. In this study, 575 participants who had been vaccinated with two or three doses of the inactivated vaccine were recruited. Serum samples were collected and tested for anti-spike IgG and neutralizing antibodies against SARS-CoV-2 (original strain, Dela, and Omicron). Unsurprisingly, a third dose of the vaccine significantly enhanced antibody responses against SARS-CoV-2 and its variants. However, despite a booster dose, the neutralizing antibody levels against Omicron, particularly the BA.5.2 subvariant, remained low. There was no sex bias, but an age bias was observed. Notably, the predominant IgG subclass antibodies were IgG1 and IgG2, with a much lower level of IgG4. After the booster shot, the ratio of IgG4 to IgG1 significantly increased. The observation of IgG1 to the IgG4 class switch after repeated inactivated vaccinations underscores the importance of continuous monitoring of subclass antibody responses. Further clinical investigations are required to understand the implications of this class switch for optimizing immunization strategies.

Update on Omicron variant and its threat to vulnerable populations

Objective

To reduce the incidence of severe illness and fatalities, and promote the awareness of protection and precaution, increased vaccination, strengthen the physical fitness, frequent ventilation, and health education should be enhanced among vulnerable populations as essential measures for the future control of COVID-19.

Study design

Systematic review.

Method

The search was done using PubMed, EMBASE and Web of Science for studies without language restrictions, published up through March 2023, since their authoritative and comprehensive literature search database. Eighty articles were included. Extraction of articles and quality assessment of included reviews was performed independently by two authors using the AMSTAR 2 score.

Results

The articles in the final data set included research on epidemiological characteristics, pathogenicity, available vaccines, treatments and epidemiological features in special populations including the elders, pregnant women, kids, people with chronic diseases concerning Omicron.

Conclusion

Although less pathogenic potential is found in Omicron, highly mutated forms have enhanced the ability of immune evasion and resistance to existing vaccines compared with former variants. Severe complications and outcomes may occur in vulnerable populations. Infected pregnant women are more likely to give birth prematurely, and fatal implications in children infected with Omicron are hyperimmune response and severe neurological disorders. In immunocompromised patients, there is a greater reported mortality and complication compared to patients with normal immune systems. Therefore, maintain social distancing, wear masks, and receive vaccinations are effective long-term measures.

Effectiveness of different booster vaccine combinations against SARS-CoV-2 during a six-month follow-up in Mexico and Argentina

Introduction

Given the limited number of patients in Latin America who have received a booster dose against the COVID-19, it remains crucial to comprehend the effectiveness of different vaccine combinations as boosters in real-world scenarios. This study aimed to assess the real-life efficacy of seven different vaccine schemes against COVID-19, including BNT162b2, ChAdOx1-S, Gam-COVID-Vac, and CoronaVac as primary schemes with either BNT162b2 or ChAdOx1-S as booster vaccines.

Methods

In this multicentric longitudinal observational study, participants from Mexico and Argentina were followed for infection and SARS-CoV-2 Spike 1-2 IgG antibodies during their primary vaccination course and for 185 days after the booster dose.

Results

A total of 491 patients were included, and the booster dose led to an overall increase in the humoral response for all groups. Patients who received BNT162b2 exhibited the highest antibody levels after the third dose, while those with primary Gam-COVID-Vac maintained a higher level of antibodies after six months. Infection both before vaccination and after the booster dose, and Gam-COVIDVac + BNT162b2 combination correlated with higher antibody titers.

Discussion

The sole predictor of infection in the six-month follow-up was a prior COVID-19 infection before the vaccination scheme, which decreased the risk of infection, and all booster vaccine combinations conveyed the same amount of protection.

Adjuvant-dependent impact of inactivated SARS-CoV-2 vaccines during heterologous infection by a SARS-related coronavirus

Whole virus-based inactivated SARS-CoV-2 vaccines adjuvanted with aluminum hydroxide have been critical to the COVID-19 pandemic response. Although these vaccines are protective against homologous coronavirus infection, the emergence of novel variants and the presence of large zoonotic reservoirs harboring novel heterologous coronaviruses provide significant opportunities for vaccine breakthrough, which raises the risk of adverse outcomes like vaccine-associated enhanced respiratory disease. Here, we use a female mouse model of coronavirus disease to evaluate inactivated vaccine performance against either homologous challenge with SARS-CoV-2 or heterologous challenge with a bat-derived coronavirus that represents a potential emerging disease threat. We show that inactivated SARS-CoV-2 vaccines adjuvanted with aluminum hydroxide can cause enhanced respiratory disease during heterologous infection, while use of an alternative adjuvant does not drive disease and promotes heterologous viral clearance. In this work, we highlight the impact of adjuvant selection on inactivated vaccine safety and efficacy against heterologous coronavirus infection.

Impact of Prior COVID-19 Immunization and/or Prior Infection on Immune Responses and Clinical Outcomes

Cellular and humoral immunity exhibit dynamic adaptation to the mutating SARS-CoV-2 virus. It is noteworthy that immune responses differ significantly, influenced by whether a patient has received vaccination or whether there is co-occurrence of naturally acquired and vaccine-induced immunity, known as hybrid immunity. The different immune reactions, conditional on vaccination status and the viral variant involved, bear implications for inflammatory responses, patient outcomes, pathogen transmission rates, and lingering post-COVID conditions. Considering these developments, we have performed a review of recently published literature, aiming to disentangle the intricate relationships among immunological profiles, transmission, the long-term health effects post-COVID infection poses, and the resultant clinical manifestations. This investigation is directed toward understanding the variability in the longevity and potency of cellular and humoral immune responses elicited by immunization and hybrid infection.

Finally neutralizing the threat? A novel SARS-CoV-2 vaccine platform that elicits enhanced neutralizing antibody responses

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) outbreak took the world by storm due to its rapid global spread and unpredictable disease outcomes. The extraordinary ascension of SARS-CoV-2 to pandemic status motivated a world-wide effort to rapidly develop vaccines that could effectively suppress virus spread and mitigate severe disease. These efforts culminated in the development and deployment of several highly effective vaccines that were heralded as the beginning-of-the-end of the pandemic. However, these successes were short lived due to the unexpected and continuous emergence of more transmissible and immune-evasive SARS-CoV-2 variants. Thus, attention has shifted toward developing novel vaccine platforms that elicit more robust and sustained neutralizing antibody responses. Recent findings by Muñoz-Alía and colleagues address this by combining a live recombinant measles vaccine platform with novel biochemical approaches to generate vaccine candidates that bolster the potency of neutralizing antibody responses against diverse SARS-CoV-2 spike proteins (M. Á. Muñoz-Alía, R. A. Nace, B. Balakrishnan, L. Zhang, et al., mBio 9:e02928-23, 2024, https://doi.org/10.1128/mbio.02928-23).

Persistent immune imprinting occurs after vaccination with the COVID-19 XBB.1.5 mRNA booster in humans

Immune imprinting describes how the first exposure to a virus shapes immunological outcomes of subsequent exposures to antigenically related strains. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) Omicron breakthrough infections and bivalent COVID-19 vaccination primarily recall cross-reactive memory B cells induced by prior Wuhan-Hu-1 spike mRNA vaccination rather than priming Omicron-specific naive B cells. These findings indicate that immune imprinting occurs after repeated Wuhan-Hu-1 spike exposures, but whether it can be overcome remains unclear. To understand the persistence of immune imprinting, we investigated memory and plasma antibody responses after administration of the updated XBB.1.5 COVID-19 mRNA vaccine booster. We showed that the XBB.1.5 booster elicited neutralizing antibody responses against current variants that were dominated by recall of pre-existing memory B cells previously induced by the Wuhan-Hu-1 spike. Therefore, immune imprinting persists after multiple exposures to Omicron spikes through vaccination and infection, including post XBB.1.5 booster vaccination, which will need to be considered to guide future vaccination.

Post-vaccination SARS-CoV-2 IgG spike antibody responses among clinical and non-clinical healthcare workers at a tertiary facility in Kenya

INTRODUCTION

Following the coronavirus disease 19 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, vaccination became the main strategy against disease severity and even death. Healthcare workers were considered high-risk for infection and, thus, were prioritised for vaccination.

METHODS

A follow-up to a SARS-CoV-2 seroprevalence study among clinical and non-clinical HCWs at the Aga Khan University Hospital, Nairobi, we assessed how vaccination influenced SARS-CoV-2 anti-spike IgG antibody responses and kinetics. Blood samples were drawn at two points spanning 6 to 18 months post-vaccination, and SARS-CoV-2 spike antibody levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Almost all participants, 98% (961/981), received a second vaccine dose, and only 8.5% (83/981) received a third dose. SARS-CoV-2 spike IgG antibodies were detected in 100% (961/961) and 92.7% (707/762) of participants who received two vaccine doses, with the first and second post-vaccine test, respectively, and in 100% (83/83) and 91.4% (64/70) of those who received three vaccine doses at the first and second post-vaccine test, respectively. Seventy-six participants developed mild infections, not requiring hospitalisation even after receiving primary vaccination. Receiving three vaccine doses influenced the anti-spike S/Co at both the first (p<0.001) and second post-vaccination testing (p<0.001). Of those who tested SARS-CoV-2 positive, the anti-spike S/Co ratio was significantly higher than those who were seronegative at the first post-vaccine test (p = 0.001). Side effects were reported by almost half of those who received the first dose, 47.3% (464/981), 28.9% (278/961) and 25.3% (21/83) of those who received the second and third vaccine doses, respectively.

DISCUSSION AND CONCLUSION

Following the second dose of primary vaccination, all participants had detectable anti-spike antibodies. The observed mild breakthrough infections may have been due to emerging SARS-CoV-2 variants. Findings suggest that although protective antibodies are induced, vaccination protected against COVID-19 disease severity and not necessarily infection.

SARS-CoV-2 antibody vaccine response in Inflammatory Bowel Disease patients with positive anti-nucleocapsid serology or history of COVID-19 infection

Background

Previous history of COVID-19 infection is a natural booster of the vaccine response in the general population. The response to COVID-19 vaccines is lessened in Inflammatory Bowel Disease patients on selected class of immunosuppressive treatments.

Aims

The study was to assess anti-SARS-CoV-2 spike-specific IgG antibody response in Inflammatory Bowel Disease patients with a history of COVID-19 infection.

Patients and methods

This single-center prospective study involved 504 Inflammatory Bowel Disease patients. Demographic data and clinical data were gathered through questionnaires and patient charts. Anti-SARS-CoV-2 spike-specific and antinucleocapsid antibody levels were measured at T1, T2 (after the 2-dose series), and T3 or T4 (booster vaccine).

Results

This study included 504 Inflammatory Bowel Disease patients, and 234 completed one year follow-up with blood tests. Positive anti-nucleocapsid serology or history of COVID-19 infection was significantly associated with increased median anti- SARS-CoV-2 spike-specific IgG titers after the 2-dose series (1930 BAU/mL vs. 521 BAU/mL p < 0.0001) and the booster vaccine (4390 BAU/mL vs. 2160 BAU/mL, p = 0.0156). Multivariate analysis showed that higher anti-SARS-CoV-2 spike-specific IgG levels were independently associated with anti-nucleocapsid antibodies at T2 (OR=2.23, p < 0.0001) and T3 (OR=1.72, p = 0.00011). Immunosuppressive treatments did not impact the antibody response or levels in patients with a history of COVID-19 infection or positive anti-nucleocapsid serology.

Conclusions

In Inflammatory Bowel Disease, prior COVID-19 infection or positive anti-nucleocapsid serology leads to increased anti-SARS-CoV-2 spike-specific IgG levels after vaccination, regardless of immunosuppressive treatments. This emphasizes the significance of accounting for previous infection in vaccination approaches.

A mini review of reinfection with the SARS-CoV-2 Omicron variant

Background

COVID-19 has caused severe morbidity and mortality worldwide. After the end of the dynamic zero-COVID policy in China in December, 2022, concerns regarding reinfection were raised while little was known due to the lack of surveillance data in this country.

Aims

This study reviews the probability, risk factors, and severity of severe acute respiratory syndrome coronavirus 2 Omicron variant reinfection, as well as the interval between infections, risk of onward transmission by reinfected cases, and the role of booster vaccination against reinfection.

Sources

References for this review were identified through searches of PubMed and Web of Science up to September 24, 2023.

Results

The rate of reinfection ranges from 3.1% to 13.0%. Factors associated with a higher risk of reinfection include being female, having comorbidities, and being unvaccinated. Reinfection with the BA.4 or BA.5 variant occurs approximately 180 days after the initial infection. Reinfections are less clinically severe than primary infections, and there is evidence of lower transmissibility. The debate surrounding the effectiveness and feasibility of booster vaccinations in preventing reinfection continues.

Conclusions

The reinfection rate during the Omicron epidemic is significantly higher than in previous epidemic periods. However, the symptoms and infectivity of reinfection were weaker than those of the prior infection. Medical staff and individuals at high risk of reinfection should be vigilant. The efficacy of booster vaccinations in reducing reinfection is currently under debate.

Comparative single-cell RNA sequencing analysis of immune response to inactivated vaccine and natural SARS-CoV-2 infection

Uncovering the immune response to an inactivated SARS-CoV-2 vaccine (In-Vac) and natural infection is crucial for comprehending COVID-19 immunology. Here we conducted an integrated analysis of single-cell RNA sequencing (scRNA-seq) data from serial peripheral blood mononuclear cell (PBMC) samples derived from 12 individuals receiving In-Vac compared with those from COVID-19 patients. Our study reveals that In-Vac induces subtle immunological changes in PBMC, including cell proportions and transcriptomes, compared with profound changes for natural infection. In-Vac modestly upregulates IFN-α but downregulates NF-κB pathways, while natural infection triggers hyperactive IFN-α and NF-κB pathways. Both In-Vac and natural infection alter T/B cell receptor repertoires, but COVID-19 has more significant change in preferential VJ gene, indicating a vigorous immune response. Our study reveals distinct patterns of cellular communications, including a selective activation of IL-15RA/IL-15 receptor pathway after In-Vac boost, suggesting its potential role in enhancing In-Vac-induced immunity. Collectively, our study illuminates multifaceted immune responses to In-Vac and natural infection, providing insights for optimizing SARS-CoV-2 vaccine efficacy.

Single MVA-SARS-2-ST/N Vaccination Rapidly Protects K18-hACE2 Mice against a Lethal SARS-CoV-2 Challenge Infection

The sudden emergence of SARS-CoV-2 demonstrates the need for new vaccines that rapidly protect in the case of an emergency. In this study, we developed a recombinant MVA vaccine co-expressing SARS-CoV-2 prefusion-stabilized spike protein (ST) and SARS-CoV-2 nucleoprotein (N, MVA-SARS-2-ST/N) as an approach to further improve vaccine-induced immunogenicity and efficacy. Single MVA-SARS-2-ST/N vaccination in K18-hACE2 mice induced robust protection against lethal respiratory SARS-CoV-2 challenge infection 28 days later. The protective outcome of MVA-SARS-2-ST/N vaccination correlated with the activation of SARS-CoV-2-neutralizing antibodies (nABs) and substantial amounts of SARS-CoV-2-specific T cells especially in the lung of MVA-SARS-2-ST/N-vaccinated mice. Emergency vaccination with MVA-SARS-2-ST/N just 2 days before lethal SARS-CoV-2 challenge infection resulted in a delayed onset of clinical disease outcome in these mice and increased titers of nAB or SARS-CoV-2-specific T cells in the spleen and lung. These data highlight the potential of a multivalent COVID-19 vaccine co-expressing S- and N-protein, which further contributes to the development of rapidly protective vaccination strategies against emerging pathogens.

Visual analysis of hotspots and trends in long COVID research based on bibliometric

After severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, a series of symptoms may persist for a long time, which is now called long COVID. It was found that long COVID can affect all patients with COVID-19. Therefore, long COVID has become a hot topic. In this study, we used the WOS database as a sample data source to conduct a bibliometric and visual analysis of 1765 long COVID articles over the past three years through VOSviewer and R package. The results show that countries/authors in Europe and The United States of America contribute most of the articles, and their cooperation is also the most active. Keyword co-occurrence identified four clusters, with important topics including the mechanism, clinical symptoms, epidemiological characteristics, and management/treatment of long COVID. Themes such as "cognitive impairment", "endothelial dysfunction", "diagnosis", and "biomarkers" are likely to be the focus of new attention in the coming period. In addition, we put forward the possible research opportunities on long COVID for researchers and practitioners to facilitate future research.

Heterologous Booster Immunization Based on Inactivated SARS-CoV-2 Vaccine Enhances Humoral Immunity and Promotes BCR Repertoire Development

Recent studies have indicated that sequentially administering SARS-CoV-2 vaccines can result in increased antibody and cellular immune responses. In this study, we compared homologous and heterologous immunization strategies following two doses of inactivated vaccines in a mouse model. Our research demonstrates that heterologous sequential immunization resulted in more immune responses displayed in the lymph node germinal center, which induced a greater number of antibody-secreting cells (ASCs), resulting in enhanced humoral and cellular immune responses and increased cross-protection against five variant strains. In further single B-cell analysis, the above findings were supported by the presence of unique B-cell receptor (BCR) repertoires and diversity in CDR3 sequence profiles elicited by a heterologous booster immunization strategy.

Effect of second booster vaccination on clinical outcomes of Omicron-variant breakthrough infection: A propensity score matching cohort study

OBJECTIVE

To further explore the effect of vaccination regimen and frequency on clinical outcomes of breakthrough infections caused by the Omicron variant, as well as the durability of vaccine effectiveness.

METHODS

A retrospective, propensity score matching, real-world cohort study was conducted. Vaccination frequency was categorized into regular vaccination, first booster, and second booster.

RESULTS

A total of 7428 cases were included, with 3910 (53 %) being male. The median age was 39 years. BA.2 than BA.5/5.2 infection presented with more pulmonary symptoms and fewer influenza-like symptoms. Among the 3516 cases of BA.5/5.2 breakthrough infections, patients who received the second booster than the first booster or regular vaccination had higher first IgM and IgG titers and first cycle thredhold values for N gene on admission, a lower percentage of fever, lower peak body temperatures, and a higher percentage of asymptomatic cases. Patients who received the first booster vaccinated with homologous mRNA or heterologous inactivated plus mRNA vaccines than homologous inactivated vaccines had higher first IgM and IgG titers, a higher percentage of asymptomatic cases, and a lower percentage of fever. Moreover, significantly different first IgG titers were observed among patients receiving the second booster vaccinated with any of the three regimens. There was no statistical difference between booster regimens of homologous mRNA vaccines and heterologous inactivated plus mRNA vaccines. Patients in Month 7- than Month 0-6 after the first booster had lower first IgM and IgG titers and first cycle thredhold values, a lower percentage of asymptomatic cases, and a higher percentage of fever; and a higher percentage of pneumonia after the second booster.

CONCLUSIONS

Repeated booster vaccinations every six months, with priority given to heterologous mRNA vaccine booster regimens in countries previously primarily using inactivated vaccines, may provide protection for adult patients with Omicron-variant breakthrough infections and improve clinical outcomes.

Evaluation of antibody and T Cell immunity response in different immunization groups of inactive and mRNA COVID-19 vaccines

This study aimed to evaluate the antibody and T cell responses of homologous and heterologous booster doses for SARS-CoV-2 vaccines. Our study was performed on those with two doses of mRNA vaccine BNT162b2 (2B, n:44), those with heterologous booster dose BNT162b2 vaccine after two doses of inactivated vaccine CoronaVac (2S+1B, n:44), those with homologous booster dose vaccine CoronaVac after two doses of vaccine CoronaVac (3S, n:44) SARS-CoV-2 IgG antibody levels were significantly higher in individuals who received heterologous boosters(p<0.001). IFN-Ɣ, IL-2 and IL-13 median values were detected higher in 2S+1B group than in 3S group, respectively (p=0.112, p=0.057, p=0.341). Although the antibody levels in 2S+1B group were similar (p=0.153) to the 2B group; IFN-Ɣ, IL-2 and IL-13 levels were higher (p<0.001). In conclusion, supplementing an improved strategy based on inactivated vaccines with an mRNA vaccine as a heterologous booster is likely to be more beneficial in the course of the pandemic.

Development of an RBD-Fc fusion vaccine for COVID-19

Although the global pandemic of SARS-CoV-2 has passed, there are still regional outbreaks that continue to jeopardize human health. Hence, there is still a great deal of interest in developing an efficient vaccine that can quickly and effectively prevent reemerging outbreaks of SARS-CoV-2. Delta variant was once a dominant strain in the world in 2021, and we first constructed a recombinant RBDdelta-Fc fusion vaccine by coupling the RBD of Delta variant with the human Fc fragment. This Fc fusion strategy increases the immunogenicity of the recombinant RBD vaccine, with a long-lasting high level of IgG antibodies and neutralizing antibodies induced by RBDdelta-Fc vaccine. This RBDdelta-Fc vaccine, as well as the RBD-Fc vaccine prepared in our previously study, could trigger a durable immune effect by the heterologous boosting immunity, and the RBD-Fc induced a quicker humoral immune response than the homologous immunization with inactivated vaccines. In conclusion, the Fc fusion strategy has a significant role in enhancing the immunogenicity of recombinant protein vaccines, thus promising the development of a safe and efficient vaccine for the heterologous boosting against SARS-CoV-2.

Immunogenicity and safety of boosting with a recombinant two-component SARS-CoV-2 vaccine: two randomized, parallel-controlled, phase 2 studies

BACKGROUND

Recombinant protein vaccines are vital for broad protection against SARS-CoV-2 variants. This study assessed ReCOV as a booster in two Phase 2 trials.

RESEARCH DESIGN AND METHODS

Study-1 involved subjects were randomized (1:1:1) to receive 20 μg ReCOV, 40 μg ReCOV, or an inactivated vaccine (COVILO®) in the United Arab Emirates. Study-2 participating individuals were randomized (1:1:1) to receive 20 μg ReCOV (pilot batch, ReCOV HA), 20 μg ReCOV (commercial batch, ReCOV TC), or 30 μg BNT162b2 (COMIRNATY®) in the Philippines. The primary immunogenicity objectives was to compare the geometric mean titer (GMT) and seroconversion rate (SCR) of neutralizing antibodies induced by one ReCOV booster dose with those of inactivated vaccine and BNT162b2, respectively, at 14 days post-booster.

RESULTS

Heterologous ReCOV booster doses were safe and induced comparable immune responses to inactivated vaccines and BNT162b2 against Omicron variants and the prototype. They showed significant advantages in cross-neutralization against multiple SARS-CoV-2 variants, surpassing inactivated vaccines and BNT162b2, with good immune persistence.

CONCLUSIONS

Heterologous ReCOV boosting was safe and effective, showing promise in combating COVID-19. The study highlights ReCOV's potential for enhanced protection, supported by strong cross-neutralization and immune persistence.

CLINICAL TRIAL REGISTRATION

Study-1, www.clinicaltrials.gov, identifier is NCT05323435; Study-2, www.clinicaltrials.gov, identifier is NCT05084989.

Evidence synthesis and pooled analysis of vaccine effectiveness for COVID-19 mRNA vaccine BNT162b2 as a heterologous booster after inactivated SARS-CoV-2 virus vaccines

Introduction of primary COVID-19 vaccination has helped reduce severe disease and death caused by SARS-CoV-2 infection. Understanding the protection conferred by heterologous booster regimens informs alternative vaccination strategies that enable programmatic resilience and can catalyze vaccine confidence and coverage. Inactivated SARS-CoV-2 vaccines are among the most widely used vaccines worldwide. This review synthesizes the available evidence identified as of May 26, 2022, on the safety, immunogenicity, and effectiveness of a heterologous BNT162b2 (Pfizer-BioNTech) mRNA vaccine booster dose after an inactivated SARS-CoV-2 vaccine primary series, to help protect against COVID-19. Evidence showed that the heterologous BNT16b2 mRNA vaccine booster enhances immunogenicity and improves vaccine effectiveness against COVID-19, and no new safety concerns were identified with heterologous inactivated primary series with mRNA booster combinations.

Heterologous Omicron-adapted vaccine as a secondary booster promotes neutralizing antibodies against Omicron and its sub-lineages in mice

Over one billion people have received 2-3 dosages of an inactivated COVID-19 vaccine for basic immunization. Whether a booster dose should be delivered to protect against the Omicron variant and its sub-lineages, remains controversial. Here, we tested different vaccine platforms targeting the ancestral or Omicron strain as a secondary booster of the ancestral inactivated vaccine in mice. We found that the Omicron-adapted inactivated viral vaccine promoted a neutralizing antibody response against Omicron in mice. Furthermore, heterologous immunization with COVID-19 vaccines based on different platforms remarkably elevated the levels of cross- neutralizing antibody against Omicron and its sub-lineages. Omicron-adapted vaccines based on heterologous platforms should be prioritized in future vaccination strategies to control COVID-19.

Safety and immunogenicity of the third and fourth doses of vaccine against SARS-CoV-2 following a 2-dose regimen of inactivated whole-virion SARS-CoV-2 vaccine

This study followed healthcare personnel (HCP) who had completed a primary series of CoronaVac and then received the third and fourth doses of COVID-19 vaccine. The primary objective was to determine the seroconversion rate of neutralizing antibodies against wild-type SARS-CoV-2 and VOCs at day 28 after the third dose of vaccine and day 28 after the fourth dose of vaccine. This prospective cohort study was conducted at Maharaj Nakorn Chiang Mai Hospital, a tertiary care hospital affiliated to Chiang Mai University from July 2021 to February 2022. Two hundred and eighty-three participants were assessed for eligibility; 142 had received AZD1222 and 141 BNT162b2 as the third dose. Seroconversion rates using a 30% inhibition cutoff value against wild-type SARS-CoV-2 were 57.2%, 98.6%, 97.8%, and 98.9% at points before and after the third dose, before and after the fourth dose, respectively among those receiving AZD1222 as the third dose. Frequencies were 31.9%, 99.3%, 98.9%, and 100% among those receiving BNT162b2 as the third dose, respectively. The seroconversion rates against B.1.1.529 [Omicron] were 76.1% and 90.2% (p-value 0.010) at 4 weeks after the third dose in those receiving AZD1222 and BNT162b2 as the third dose, respectively. After a booster with the mRNA vaccine, the seroconversion rates increased from 21.7 to 91.3% and from 30.4 to 91.3% in those receiving AZD1222 and BNT162b2 as the third dose, respectively. No serious safety concerns were found in this study. In conclusion, antibody responses waned over time regardless of the vaccine regimen. The booster dose of the vaccine elicited a humoral immune response against SARS-CoV-2 including SARS-CoV-2 variants of concern, including B.1.1.529 [Omicron], which was circulating during the study period. However, the results might not be extrapolated to other Omicron sublineages.

Longitudinal study of disease severity and external factors in cognitive failure after COVID-19 among Indonesian population

The COVID-19 infection is assumed to induce cognitive failure. Identifying the relationship between COVID-19, the effect of vaccination and medication, and accommodating non-COVID-19 factors to cognitive failure is essential. This study was conducted in Indonesia from September 2021 to January 2023. Demographic information, clinical data, comorbidities, vaccination, and medication during COVID-19 were obtained, as well as a 6-month cognitive assessment with Cognitive Failures Questionnaire/CFQ, Fatigue Severity Score, and Generalized Anxiety Disorder (GAD-7). A Structural Equation Model explains the relationship between potential predictors and cognitive failure. The average score of CFQ after 6 months was 45.6 ± 23.1 out of 100. The severity of the disease, which was associated with vaccination status, age, previous infection, and unit of treatment (p < 0.05), was not related to cognitive failure (p = 0.519), although there is a significant direct impact of worst vaccination status to cognitive failure(p < 0.001). However, age, fatigue, and current anxiety were associated with higher cognitive failure (p < 0.001), although comorbidities and recent headaches were not significant in other models (p > 0.05). This study concludes that cognitive failure after COVID-19 is a multifactorial event and does not solely depend on COVID-19 severity. It is crucial to re-address the factors related to the long-term efficacy of vaccination and medication and focus on non-health factors affecting cognitive failure.Trial Registration: NCT05060562.

Adjuvant-dependent effects on the safety and efficacy of inactivated SARS-CoV-2 vaccines during heterologous infection by a SARS-related coronavirus

Inactivated whole virus SARS-CoV-2 vaccines adjuvanted with aluminum hydroxide (Alum) are among the most widely used COVID-19 vaccines globally and have been critical to the COVID-19 pandemic response. Although these vaccines are protective against homologous virus infection in healthy recipients, the emergence of novel SARS-CoV-2 variants and the presence of large zoonotic reservoirs provide significant opportunities for vaccine breakthrough, which raises the risk of adverse outcomes including vaccine-associated enhanced respiratory disease (VAERD). To evaluate this possibility, we tested the performance of an inactivated SARS-CoV-2 vaccine (iCoV2) in combination with Alum against either homologous or heterologous coronavirus challenge in a mouse model of coronavirus-induced pulmonary disease. Consistent with human results, iCoV2 + Alum protected against homologous challenge. However, challenge with a heterologous SARS-related coronavirus, Rs-SHC014-CoV (SHC014), up to at least 10 months post-vaccination, resulted in VAERD in iCoV2 + Alum-vaccinated animals, characterized by pulmonary eosinophilic infiltrates, enhanced pulmonary pathology, delayed viral clearance, and decreased pulmonary function. In contrast, vaccination with iCoV2 in combination with an alternative adjuvant (RIBI) did not induce VAERD and promoted enhanced SHC014 clearance. Further characterization of iCoV2 + Alum-induced immunity suggested that CD4+ T cells were a major driver of VAERD, and these responses were partially reversed by re-boosting with recombinant Spike protein + RIBI adjuvant. These results highlight potential risks associated with vaccine breakthrough in recipients of Alum-adjuvanted inactivated vaccines and provide important insights into factors affecting both the safety and efficacy of coronavirus vaccines in the face of heterologous virus infections.

MicroRNAs Derived from Extracellular Vesicles: Keys to Understanding SARS-CoV-2 Vaccination Response in Cancer Patients?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) provoked a global pandemic identified as coronavirus disease (COVID-19), with millions of deaths worldwide. However, several important questions regarding its impact on public health remain unanswered, such as the impact of vaccination on vulnerable subpopulations such as cancer patients. Cytokine storm and a sustained inflammatory state are commonly associated with immune cell depletion, being manifested in most immunocompromised individuals. This strong immunosuppression can lead to a dysfunctional antiviral response to natural viral infection and compromised vaccination response. Extracellular vesicles (EVs) are membrane-bound vesicles released from cells that are involved in intercellular communication. EVs carry various molecules including microRNAs that play a crucial role in COVID-19 pathophysiology, influencing cellular responses. This review summarizes the state of the art concerning the role of EV-derived miRNAs in COVID-19 infection and their potential use as prognosis biomarkers for vaccination response in cancer patients.

Safety and immunogenicity of Ad5-nCoV immunization after three-dose priming with inactivated SARS-CoV-2 vaccine in Chinese adults

Data on the safety and immunity of a heterologous booster (fourth dose) after three-doses of inactivated SARS-CoV-2 vaccine in Chinese adults are limited. We evaluate the safety and immunogenicity of Ad5-nCoV in a randomized, double-blind, parallel-controlled phase 4 clinical trial in Zhejiang, China (NCT05373030). Participants aged 18-80 years (100 per group), administered three doses of inactivated SARS-CoV-2 vaccine ≥6 months earlier, are enrolled and randomized 1:1 into two groups, which are administered intramuscular Ad5-nCoV or inactivated SARS-CoV-2 vaccine (CoronaVac or Covilo). All observed adverse reactions are predictable and manageable. Ad5-nCoV elicits significantly higher RBD-specific IgG levels, with a geometric mean concentration of 2924.0 on day 14 post-booster, 7.8-fold that of the inactivated vaccine. Pseudovirus-neutralizing antibodies to Omicron BA.4/5 show a similar pattern, with geometric mean titers of 228.9 in Ad5-nCoV group and 65.5 in inactivated vaccine group. Ad5-nCoV booster maintains high antibody levels on day 90, with seroconversion of 71.4%, while that of inactivated vaccine is 5.2%, almost pre-booster levels. A fourth Ad5-nCoV vaccination following three-doses of inactivated SARS-CoV-2 vaccine is immunogenic, tolerable, and more efficient than inactivated SARS-CoV-2 vaccine. Ad5-nCoV elicits a stronger humoral response against Omicron BA.4/5 and maintains antibody levels for longer than homologous boosting.

Effectiveness of homologous or heterologous immunization regimens against SARS-CoV-2 after two doses of inactivated COVID-19 vaccine: A systematic review and meta-analysis

We aimed to evaluate the effectiveness or efficacy of heterologous or homologous COVID-19 vaccine regimens against COVID-19-related outcomes after primary immunization with two doses of CoronaVac or Sinopharm COVID-19 vaccines. PubMed, EMBASE, Web of Science, and Cochrane Library databases were searched up to 31 October 2022. The primary measure was vaccine effectiveness against COVID-19 infection with homologous or heterologous booster. The results showed heterologous and homologous booster significantly improved effectiveness against COVID-19 infection compared to primary immunization. The effectiveness against COVID-19 infection was 89.19% (95%CI 78.49, 99.89) for heterologous mRNA vaccine booster, 87.00% (95%CI 82.14, 91.85) for non-replicating vector vaccine booster, 69.99% (95%CI 52.16, 87.82) for homologous booster, and 51.48% (95%CI 41.75, 61.21) for two doses of inactivated vaccine. Homologous and heterologous regimens were also effective against SARS-CoV-2 variants, and more evidence is still needed to confirm our findings.

Comparison of humoral immune response in heterologous and homologous COVID-19 booster vaccine groups using CoronaVac and mRNA-based BNT162b2 vaccines

BACKGROUND

Heterologous COVID-19 booster vaccination is an alternative strategy to homologous vaccination, especially in developing countries, due to shortages, delays, or unequal distribution of COVID-19 vaccines. We compared cohorts vaccinated with different vaccine combinations to investigate whether a heterologous booster dose of mRNA-based BNT162b2 vaccine boosts the immune response in individuals primed with the CoronaVac vaccine.

METHODS

Anti-RBD IgG is generally measured 4 weeks after primary immunization and 4 weeks after booster vaccination. Data on anti-receptor-binding domain (anti-RBD) IgG antibody titers and clinical characteristics were provided by infection control units.

RESULTS

The highest median anti-RBD IgG antibody titers (14589 AU/mL) after primary immunization was observed in the group vaccinated with two doses of BNT162b2 vaccine. Antibody titers were lower 4 months or more after the second CoronaVac vaccine dose in CoronaVac recipients with or without previous COVID-19. In the homologous COVID-19 booster vaccine group (primed with two doses of CoronaVac 4 weeks apart and a single booster dose of CoronaVac) the median anti-RBD titers decreased from 1025 to 242 AU/mL before the booster dose. In the heterologous group (primed with two doses of CoronaVac 4 weeks apart and a single booster dose of BNT162b2), the median anti-RBD titer increased to 31624 AU/mL, a 132-fold increase, 16 days after the booster dose.

CONCLUSIONS

After the second dose of CoronaVac, protective neutralizing antibody levels decrease over time, and a booster dose is required. Heterologous COVID-19 booster vaccination with BNT162b2 is effective at boosting neutralizing antibody levels.

Breakthrough SARS-CoV-2 Omicron Variant in Individuals Primed with Heterologous Vaccines Enhances Inhibition Performance of Neutralizing Antibody to BA.2 Parental Lineage

This study aims to analyze the neutralization ability against Omicron parental variants in five clusters of individuals with different Coronavirus disease (COVID-19) immunity backgrounds, including individuals receiving a homologous or heterologous vaccine without prior infection, recovered patients with homologous or heterologous vaccination, and recovery patients without vaccination. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) surrogate virus neutralization assay was performed on serum samples. Spearman correlation analysis showed that the percent inhibition against Omicron B.1.1.529 and BA.2 was significantly related to the period of serum collection (r = 0.730 and 0.787, p < 0.001, respectively). Very strong correlation between percent inhibition of neutralizing antibody against Omicron B.1.1.529 and BA.2 variants (r_s = 0.973, p < 0.001) was also observed. The neutralizing activity of the sera from recovery patients receiving homologous and heterologous vaccine against the wild-type, B.1.1.529, and BA.2 Omicron variants was significantly higher (p < 0.001) than that of recovery patients without vaccination. This study robustly showed that the breakthrough SARS-CoV-2 Omicron variant in individuals who received homologous and heterologous vaccines had a high level of neutralizing activity against B.1.1.529 and BA.2 parental lineage of XBB subvariants. Therefore, the next-generation COVID-19 vaccine against emerging variants is needed to improve resilience against ongoing variants, particularly for persons who have never been infected.

Safety and immunogenicity of aerosolised Ad5-nCoV, intramuscular Ad5-nCoV, or inactivated COVID-19 vaccine CoronaVac given as the second booster following three doses of CoronaVac: a multicentre, open-label, phase 4, randomised trial

BACKGROUND

Aerosolised Ad5-nCoV is the first approved mucosal respiratory COVID-19 vaccine to be used as a booster after the primary immunisation with COVID-19 vaccines. This study aimed to evaluate the safety and immunogenicity of aerosolised Ad5-nCoV, intramuscular Ad5-nCoV, or inactivated COVID-19 vaccine CoronaVac given as the second booster.

METHODS

This is an open-label, parallel-controlled, phase 4 randomised trial enrolling healthy adult participants (≥18 years) who had completed a two-dose primary immunisation and a booster immunisation with inactivated COVID-19 vaccines (CoronaVac only) at least 6 months before, in Lianshui and Donghai counties, Jiangsu Province, China. We recruited eligible participants from previous trials in China (NCT04892459, NCT04952727, and NCT05043259) as cohort 1 (with the serum before and after the first booster dose available), and from eligible volunteers in Lianshui and Donghai counties, Jiangsu Province, as cohort 2. Participants were randomly assigned at a ratio of 1:1:1, using a web-based interactive response randomisation system, to receive the fourth dose (second booster) of aerosolised Ad5-nCoV (0·1 mL of 1·0 × 1011 viral particles per mL), intramuscular Ad5-nCoV (0·5 mL of 1·0 × 1011 viral particles per mL), or inactivated COVID-19 vaccine CoronaVac (0·5 mL), respectively. The co-primary outcomes were safety and immunogenicity of geometric mean titres (GMTs) of serum neutralising antibodies against prototype live SARS-CoV-2 virus 28 days after the vaccination, assessed on a per-protocol basis. Non-inferiority or superiority was achieved when the lower limit of the 95% CI of the GMT ratio (heterologous group vs homologous group) exceeded 0·67 or 1·0, respectively. This study was registered with ClinicalTrials.gov, NCT05303584 and is ongoing.

FINDINGS

Between April 23 and May 23, 2022, from 367 volunteers screened for eligibility, 356 participants met eligibility criteria and received a dose of aerosolised Ad5-nCoV (n=117), intramuscular Ad5-nCoV (n=120), or CoronaVac (n=119). Within 28 days of booster vaccination, participants in the intramuscular Ad5-nCoV group reported a significantly higher frequency of adverse reactions than those in the aerosolised Ad5-nCoV and intramuscular CoronaVac groups (30% vs 9% and 14%, respectively; p<0·0001). No serious adverse events related to the vaccination were reported. The heterologous boosting with aerosolised Ad5-nCoV triggered a GMT of 672·4 (95% CI 539·7-837·7) and intramuscular Ad5-nCoV triggered a serum neutralising antibody GMT of 582·6 (505·0-672·2) 28 days after the booster dose, both of which were significantly higher than the GMT in the CoronaVac group (58·5 [48·0-71·4]; p<0·0001).

INTERPRETATION

A heterologous fourth dose (second booster) with either aerosolised Ad5-nCoV or intramuscular Ad5-nCoV was safe and highly immunogenic in healthy adults who had been immunised with three doses of CoronaVac.

FUNDING

National Natural Science Foundation of China, Jiangsu Provincial Science Fund for Distinguished Young Scholars, and Jiangsu Provincial Key Project of Science and Technology Plan.

SARS-CoV-2 Antibody Dynamics after COVID-19 Vaccination and Infection: A Real-World Cross-Sectional Analysis

The Coronavirus disease 2019 (COVID-19) pandemic, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), continues to surge despite the widespread use of vaccination. In Thailand, more than 77% and 39% of the population received two doses and three doses of COVID-19 vaccines as of December 2022, respectively. In addition, during the Omicron predominant period in 2022, more than 70% of Thai individuals have been infected. To gain comprehensive insight into SARS-CoV-2 antibody dynamics following vaccination or following vaccination and infection (hybrid immunity), we performed a cross-sectional analysis of sera samples from individuals who received COVID-19 vaccination and/or have been infected with COVID-19 in Thailand between January 2021 and December 2022. A total of 4126 samples were collected. Humoral immunity was evaluated by quantifying the immunoglobulin (including IgG, IgM, and IgA isotypes) specific to the SARS-CoV-2 receptor-binding domain (RBD) or Ig anti-RBD. The results showed that individuals who received two-dose vaccination alone had lower levels of Ig anti-RBD, which rapidly waned over time. To restore the waning antibody, a third dose vaccination is recommended for uninfected individuals who have only received 2 doses.