Safety and Immunogenicity of the Third Booster Dose with Inactivated, Viral Vector, and mRNA COVID-19 Vaccines in Fully Immunized Healthy Adults with Inactivated Vaccine

Evidence base for yearly respiratory virus vaccines: Current status and proposed improved strategies

Annual vaccination is widely recommended for influenza and SARS-CoV-2. In this essay, we analyse and question the prevailing policymaking approach to these respiratory virus vaccines, especially in the United States. Every year, licensed influenza vaccines are reformulated to include specific strains expected to dominate in the season ahead. Updated vaccines are rapidly manufactured and approved without further regulatory requirement of clinical data. Novel vaccines (i.e. new products) typically undergo clinical trials, though generally powered for clinically unimportant outcomes (e.g. lab-confirmed infections, regardless of symptomatology or antibody levels). Eventually, the current and future efficacy of influenza and COVID-19 vaccines against hospitalization or death carries considerable uncertainty. The emergence of highly transmissible SARS-CoV-2 variants and waning vaccine-induced immunity led to plummeting vaccine effectiveness, at least against symptomatic infection, and booster doses have since been widely recommended. No further randomized trials were performed for clinically important outcomes for licensed updated boosters. In both cases, annual vaccine effectiveness estimates are generated by observational research, but observational studies are particularly susceptible to confounding and bias. Well-conducted experimental studies, particularly randomized trials, are necessary to address persistent uncertainties about influenza and COVID-19 vaccines. We propose a new research framework which would render results relevant to the current or future respiratory viral seasons. We demonstrate that experimental studies are feasible by adopting a more pragmatic approach and provide strategies on how to do so. When it comes to implementing policies that seriously impact people's lives, require substantial public resources and/or rely on widespread public acceptance, high evidence standards are desirable.

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.

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.

COVID-19 vaccination status in people with spinal cord injury: Results from a cross-sectional study in Thailand

OBJECTIVE

To assess COVID-19 vaccination status among individuals with spinal cord injury (SCI).

DESIGN

A cross-sectional study.

SETTING

Twelve hospitals from all regions of Thailand.

PARTICIPANTS

One hundred and eighty people with SCI were randomly selected from the Thai SCI registry database.

INTERVENTION

Not applicable.

OUTCOME MEASURES

The primary outcome, which was the COVID-19 vaccination status, and the secondary outcomes, which were the number of vaccination doses, satisfaction and dissatisfaction aspects, and barriers to vaccination, were recorded using a specifically developed questionnaire over the telephone during February to March 2022. Data were analyzed using descriptive analyses, bivariate, and multivariable analyses.

RESULTS

Of the 96 people with SCI who were able to respond, the prevalence of receiving at least one dose was 77% but the prevalence of receiving a booster dose was 20%. Being non-traumatic SCI correlated negatively with having received any vaccination doses when compared to traumatic SCI. Most of the participants were satisfied with the government provision of COVID-19 vaccines. The major barriers to vaccination were problems related to a negative attitude toward the vaccination, followed by transportation difficulties and wheelchair-inaccessible vaccination sites.

CONCLUSIONS

Seventy-seven percent of people with SCI participating in this study received at least one dose of the COVID-19 vaccine, whereas only 20% of them received a booster dose of the COVID-19 vaccination. To increase the prevalence of vaccination, healthcare providers should deliver the fact regarding COVID-19 vaccination to reduce negative attitudes, as well as remove physical barriers to vaccination places for people with SCI.

How do we change our approach to COVID with the changing face of disease?

INTRODUCTION

The emergence of SARS-CoV-2 triggered a global health emergency, causing > 7 million deaths thus far. Limited early knowledge spurred swift research, treatment, and vaccine developments. Implementation of public health measures such as, lockdowns and social distancing, disrupted economies and strained healthcare. Viral mutations highlighted the need for flexible strategies and strong public health infrastructure, with global collaboration crucial for pandemic control.

AREAS COVERED

(i) Revisiting diagnostic strategies, (ii) adapting to the evolving challenge of the virus, (iii) vaccines against new variants, (iv) vaccine hesitancy in the light of the evolving disease, (v) treatment strategies, (vi) hospital preparedness for changing clinical needs, (vii) global cooperation and data sharing, (viii) economic implications, and (ix) education and awareness- keeping communities informed.

EXPERT OPINION

The COVID-19 crisis forced unprecedented adaptation, emphasizing public health readiness, global unity, and scientific advancement. Key lessons highlight the importance of adaptability and resilience against uncertainties. As the pandemic evolves into a 'new normal,' ongoing vigilance, improved understanding, and available vaccines and treatments equip us for future challenges. Priorities now include proactive pandemic strategies, early warnings, supported healthcare, public education, and addressing societal disparities for better health resilience and sustainability.

Comparative Study of T-Cell Repertoires after COVID-19 Immunization with Homologous or Heterologous Vaccine Booster

Sequencing of the T-cell repertoire is an innovative method to assess the cellular responses after immunization. The purpose of this study was to compare T-cell repertoires after COVID-19 immunization with homologous (HOB) and heterologous (HEB) boosting. The study included 20 participants with a median age of 27.5 (IQR:23) years, who were vaccinated with one dose of the Ad26.COV2.S vaccine and were boosted with either Ad26.COV2.S (n = 10) or BNT162b2 (n = 10) vaccine. Analysis of the T-cell receptor beta locus (TCRβ) sequencing one month after the booster dose identified that the HEB compared to the HOB group exhibited a higher number of both total and COVID-19-related functional T-cell rearrangements [mean of total productive rearrangements (TPRs): 63151.8 (SD ± 18441.5) vs. 34915.4 (SD ± 11121.6), p = 0.001 and COVID-19-TPRs: 522.5 (SD ± 178.0) vs. 298.3 (SD ± 101.1), p = 0.003]. A comparison between the HOB and HEB groups detected no statistically significant differences regarding T-cell Simpson clonality [0.021 (IQR:0.014) vs. 0.019 (IQR:0.007)], richness [8734.5 (IQR:973.3) vs. 8724 (IQR:383.7)] and T-cell fraction [0.19 (IQR:0.08) vs. 0.18 (IQR:0.08)]. HEB also exhibited a substantially elevated humoral immune response one month after the booster dose compared to HOB [median antibody titer (IQR): 10115.0 U/mL (6993.0) vs. 1781.0 U/mL (1314.0), p = 0.001]. T-cell repertoire sequencing indicated that HEB had increased SARS-CoV-2-related T-cell rearrangements, which was in accordance with higher humoral responses and possibly conferring longer protection. Data from the present study indicate that the administration of different COVID-19 vaccines as a booster may provide better protection.

Immunogenicity and safety of RAZI recombinant spike protein vaccine (RCP) as a booster dose after priming with BBIBP-CorV: a parallel two groups, randomized, double blind trial

BACKGROUND

The immunity induced by primary vaccination is effective against COVID-19; however, booster vaccines are needed to maintain vaccine-induced immunity and improve protection against emerging variants. Heterologous boosting is believed to result in more robust immune responses. This study investigated the safety and immunogenicity of the Razi Cov Pars vaccine (RCP) as a heterologous booster dose in people primed with Beijing Bio-Institute of Biological Products Coronavirus Vaccine (BBIBP-CorV).

METHODS

We conducted a randomized, double-blind, active-controlled trial in adults aged 18 and over primarily vaccinated with BBIBP-CorV, an inactivated SARS-CoV-2 vaccine. Eligible participants were randomly assigned (1:1) to receive a booster dose of RCP or BBIBP-CorV vaccines. The primary outcome was neutralizing antibody activity measured by a conventional virus neutralization test (cVNT). The secondary efficacy outcomes included specific IgG antibodies against SARS-CoV-2 spike (S1 and receptor-binding domain, RBD) antigens and cell-mediated immunity. We measured humoral antibody responses at 2 weeks (in all participants) and 3 and 6 months (a subgroup of 101 participants) after the booster dose injection. The secondary safety outcomes were solicited and unsolicited immediate, local, and systemic adverse reactions.

RESULTS

We recruited 483 eligible participants between December 7, 2021, and January 13, 2022. The mean age was 51.9 years, and 68.1% were men. Neutralizing antibody titers increased about 3 (geometric mean fold increase, GMFI = 2.77, 95% CI 2.26-3.39) and 21 (GMFI = 21.51, 95% CI 16.35-28.32) times compared to the baseline in the BBIBP-CorV and the RCP vaccine groups. Geometric mean ratios (GMR) and 95% CI for serum neutralizing antibody titers for RCP compared with BBIBP-CorV on days 14, 90, and 180 were 6.81 (5.32-8.72), 1.77 (1.15-2.72), and 2.37 (1.62-3.47) respectively. We observed a similar pattern for specific antibody responses against S1 and RBD. We detected a rise in gamma interferon (IFN-γ), tumor necrosis factor (TNF-α), and interleukin 2 (IL-2) following stimulation with S antigen, particularly in the RCP group, and the flow cytometry examination showed an increase in the percentage of CD3 + /CD8 + lymphocytes. RCP and BBIBP-CorV had similar safety profiles; we identified no vaccine-related or unrelated deaths.

CONCLUSIONS

BBIBP-CorV and RCP vaccines as booster doses are safe and provide a strong immune response that is more robust when the RCP vaccine is used. Heterologous vaccines are preferred as booster doses.

TRIAL REGISTRATION

This study was registered with the Iranian Registry of Clinical Trial at www.irct.ir , IRCT20201214049709N4. Registered 29 November 2021.

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.

Immunogenicity and durability against Omicron BA.1, BA.2 and BA.4/5 variants at 3-4 months after a heterologous COVID-19 booster vaccine in healthy adults with a two-doses CoronaVac vaccination

Background

Several countries have authorized a booster vaccine campaign to combat the spread of COVID-19. Data on persistence of booster vaccine-induced immunity against new Omicron subvariants are still limited. Therefore, our study aimed to determine the serological immune response of COVID-19 booster after CoronaVac-priming.

Methods

A total of 187 CoronaVac-primed participants were enrolled and received an inactivated (BBIBP), viral vector (AZD1222) or mRNA vaccine (full-/half-dose BNT162B2, full-/half-dose mRNA-1273) as a booster dose. The persistence of humoral immunity both binding and neutralizing antibodies against wild-type and Omicron was determined on day 90-120 after booster.

Results

A waning of total RBD immunoglobulin (Ig) levels, anti-RBD IgG, and neutralizing antibodies against Omicron BA.1, BA.2, and BA.4/5 variants was observed 90-120 days after booster vaccination. Participants who received mRNA-1273 had the highest persistence of the immunogenicity response, followed by BNT162b2, AZD1222, and BBIBP-CorV. The responses between full and half doses of mRNA-1273 were comparable. The percentage reduction of binding antibody ranged from 50 % to 75 % among all booster vaccine.

Conclusions

The antibody response substantially waned after 90-120 days post-booster dose. The heterologous mRNA and the viral vector booster demonstrated higher detectable rate of humoral immune responses against the Omicron variant compared to the inactivated BBIBP booster. Nevertheless, an additional fourth dose is recommended to maintain immune response against infection.

Safety, immunogenicity, and efficacy of a modified COVID-19 mRNA vaccine, SW-BIC-213, in healthy people aged 18 years and above: a phase 3 double-blinded, randomized, parallel controlled clinical trial in Lao PDR (Laos)

Background

The mRNA vaccine has demonstrated significant effectiveness in protecting against SARS-CoV-2 during the pandemic, including against severe forms of the disease caused by emerging variants. In this study, we examined safety, immunogenicity, and relative efficacy of a heterologous booster of the lipopolyplex (LPP)-based mRNA vaccine (SW-BIC-213) versus a homologous booster of an inactivated vaccine (BBIBP) in Laos.

Methods

In this phase 3 clinical trial, which was randomized, parallel controlled and double-blinded, healthy adults aged 18 years and above were recruited from the Southern Savannakhet Provincial Hospital and Champhone District Hospital. The primary outcomes were safety and immunogenicity, with efficacy as an exploratory endpoint. Participants who were fully immunized with a two-dose inactivated vaccine for more than 6 months were assigned equally to either the SW-BIC-213 group (25 μg) or BBIBP group. The primary safety endpoint was to describe the safety profile of all participants in each group up to 6 months post-booster immunization. The primary immunogenic outcome was to demonstrate the superiority of the neutralizing antibody response, in terms of geometric mean titers (GMTs) of SW-BIC-213, compared with BBIBP 28 days after the booster dose. The exploratory efficacy endpoint aimed to assess the relative efficacy of SW-BIC-213 compared to BBIBP against virologically confirmed symptomatic COVID-19 over a 6-month period. The trial was registered with ClinicalTrials.gov (NCT05580159).

Findings

Between October 10, 2022, and January 13, 2023, 1200 participants were assigned to SW-BIC-213 group and 1203 participants in the BBIBP group. All adverse reactions observed during the study were tolerable, transient, and resolved spontaneously. Solicited local reactions were the main adverse reactions in both the SW-BIC-213 group (43.8%) and BBIBP group (14.8%) (p < 0.001). Heterologous boosting with SW-BIC-213 induced higher live virus neutralizing antibodies to SARS-CoV-2 wildtype and BA.5 strains with GMTs reaching 750.1 and 192.9 than homologous boosting with BBIBP with GMTs of 131.5 (p < 0.001) and 47.5 (p < 0.001) on day 29. The statistical findings revealed that, following a period of 14-day to 6-month after booster vaccination, the SW-BIC-213 group exhibited a relative vaccine efficacy (VE) of 70.1% (95% CI: 34.2-86.4) against symptomatic COVID-19 when compared to the BBIBP group.

Interpretation

A heterologous booster with the COVID-19 mRNA vaccine SW-BIC-213 manifests a favorable safety profile and proves highly immunogenic and efficacious in preventing symptomatic COVID-19 in individuals who have previously received two doses of inactivated vaccine.

Funding

Shanghai Strategic Emerging Industries Development Special Fund, Biomedical Technology Support Special Project of Shanghai "Science and Technology Innovation Action Plan", Shanghai Municipal Science and Technology Commission.

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.

Immunogenicity and reactogenicity of a first booster with BNT162b2 or full-dose mRNA-1273: A randomised VACCELERATE trial in adults ≥75 years (EU-COVAT-1)

BACKGROUND

Vaccination remains crucial for protection against severe SARS-CoV-2 infection, especially for people of advanced age, however, optimal dosing regimens are as yet lacking.

METHODS

EU-COVAT-1-AGED Part A is a randomised controlled, adaptive, multicentre phase II trial evaluating safety and immunogenicity of a 3rd vaccination (1st booster) in individuals ≥75 years. Fifty-three participants were randomised to full-doses of either mRNA-1273 (Spikevax®, 100 µg) or BNT162b2 (Comirnaty®, 30 µg). The primary endpoint was the rate of 2-fold circulating antibody titre increase 14 days post-vaccination measured by quantitative electrochemiluminescence (ECL) immunoassay, targeting RBD region of Wuhan wild-type SARS-CoV-2. Secondary endpoints included the changes in neutralising capacity against wild-type and 25 variants of concern at 14 days and up to 12 months. Safety was assessed by monitoring of solicited adverse events (AEs) for seven days after on-study vaccination. Unsolicited AEs were collected until the end of follow-up at 12 months, SAEs were pursued for a further 30 days.

RESULTS

Between 08th of November 2021 and 04th of January 2022, 53 participants ≥75 years received a COVID-19 vaccine as 1st booster. Fifty subjects (BNT162b2 n = 25/mRNA-1273 n = 25) were included in the analyses for immunogenicity at day 14. The primary endpoint of a 2-fold anti-RBD IgG titre increase 14 days after vaccination was reached for all subjects. A 3rd vaccination of full-dose mRNA-1273 provided higher anti-RBD IgG titres (Geometric mean titre) D14 mRNA-127310711 IU/mL (95 %-CI: 8003;14336) vs. BNT162b2: 7090 IU/mL (95 %-CI: 5688;8837). We detected a pattern showing higher neutralising capacity of full-dose mRNA-1273 against wild-type as well as for 23 out of 25 tested variants.

INTERPRETATION

Third doses of either BNT162b2 or mRNA-1273 provide substantial circulating antibody increase 14 days after vaccination. Full-dose mRNA-1273 provides higher antibody levels with an overall similar safety profile for people ≥75 years.

FUNDING

This trial was funded by the European Commission (Framework Program HORIZON 2020).

A two-arm analysis of the immune response to heterologous boosting of inactivated SARS-CoV-2 vaccines

Several vaccine programs were introduced during the COVID-19 pandemic, which included inactivated virus, DNA viral vectors and mRNA vaccines. Booster programs are recommended, especially for those in high-risk groups. However, many of these booster programs involve heterologous vaccines. This study enrolled volunteers who first received two full-dose CoronaVac vaccinations before receiving heterologous boosters with DNA- and/or mRNA-vaccines for an additional 2 doses (n = 40) or an additional 3 doses (n = 16). Our results showed no difference in side effects, neutralizing antibodies, or T-cell responses for any of the heterologous vaccination programs. However, the neutralizing capacity and IFN-γ responses against the Omicron variant in volunteers who received 4 or 5 doses were improved. Polarization of peripheral memory T cells after stimulation in all booster groups with Omicron peptide showed an increased trend of naïve and central memory phenotypes of both CD4+ and CD8+ T cells, suggesting that exposure to Omicron antigens will drive T cells into a lymphoid resident T cell phenotype. Our data support a continuous vaccination program to maximize the effectiveness of immunity, especially in people at high risk. Furthermore, the number of boosting doses is important for maintaining immunity.

Validation of a SARS-CoV-2 Surrogate Neutralization Test Detecting Neutralizing Antibodies against the Major Variants of Concern

SARS-CoV-2 infection and/or vaccination elicit a broad range of neutralizing antibody responses against the different variants of concern (VOC). We established a new variant-adapted surrogate virus neutralization test (sVNT) and assessed the neutralization activity against the ancestral B.1 (WT) and VOC Delta, Omicron BA.1, BA.2, and BA.5. Analytical performances were compared against the respective VOC to the reference virus neutralization test (VNT) and two CE-IVD labeled kits using three different cohorts collected during the COVID-19 waves. Correlation analyses showed moderate to strong correlation for Omicron sub-variants (Spearman's r = 0.7081 for BA.1, r = 0.7205 for BA.2, and r = 0.6042 for BA.5), and for WT (r = 0.8458) and Delta-sVNT (r = 0.8158), respectively. Comparison of the WT-sVNT performance with two CE-IVD kits, the "Icosagen SARS-CoV-2 Neutralizing Antibody ELISA kit" and the "Genscript cPass, kit" revealed an overall good correlation ranging from 0.8673 to -0.8773 and a midway profile between both commercial kits with 87.76% sensitivity and 90.48% clinical specificity. The BA.2-sVNT performance was similar to the BA.2 Genscript test. Finally, a correlation analysis revealed a strong association (r = 0.8583) between BA.5-sVNT and VNT sVNT using a double-vaccinated cohort (n = 100) and an Omicron-breakthrough infection cohort (n = 91). In conclusion, the sVNT allows for the efficient prediction of immune protection against the various VOCs.

Dynamic Antibody Response and Hybrid Immunity Following Multiple COVID-19 Vaccine Doses and Infection: A Case Study

This case study highlights the dynamic nature of the antibody response to SARS-CoV-2 in a vulnerable subject aged 70 years between 2021 and 2023. This individual had been vaccinated with six doses of the ancestral (Wuhan-Hu-1) COVID-19 vaccine and had a breakthrough infection 126 days after receiving Covovax™- (CO) as the sixth dose. The serostatus for total immunoglobulin specific to the receptor binding domain (total RBD Ig) changed from negative to positive following a two-dose CoronaVac (CV) vaccination, indicating a successful immune response. Booster doses, including AZD1222 (AZ), half-dose BNT162b2 (PF), and CO, increased the total RBD Ig levels, except for CV. The individual experienced a breakthrough infection by the Omicron BA.5 variant, leading to a substantial surge in total RBD Ig to over 105 U/mL. This generated sustained and extended antibody persistence, with the half-life of total RBD Ig lasting approximately 103.6 days. Furthermore, it has been observed that this breakthrough infection generated the highest neutralizing antibodies against BA.5, followed by XBB.1.5, BQ.1.1, and BA.2.75, respectively.

Safety, immunogenicity, and efficacy of the mRNA vaccine CS-2034 as a heterologous booster versus homologous booster with BBIBP-CorV in adults aged ≥18 years: a randomised, double-blind, phase 2b trial

BACKGROUND

Heterologous boosting is suggested to be of use in populations who have received inactivated COVID-19 vaccines. We aimed to assess the safety and immunogenicity of a heterologous vaccination with the mRNA vaccine CS-2034 versus the inactivated BBIBP-CorV as a fourth dose, as well as the efficacy against the SARS-CoV-2 omicron (BA.5) variant.

METHODS

This trial contains a randomised, double-blind, parallel-controlled study in healthy participants aged 18 years or older (group A) and an open-label cohort in participants 60 years and older (group B), who had received three doses of inactivated whole-virion vaccines at least 6 months before enrolment. Pregnant women and people with major chronic illnesses or a history of allergies were excluded. Eligible participants in group A were stratified by age (18-59 years and ≥60 years) and then randomised by SAS 9.4 in a ratio of 3:1 to receive a dose of the mRNA vaccine (CS-2034, CanSino, Shanghai, China) or inactivated vaccine (BBIBP-CorV, Sinopharm, Beijing, China). Safety and immunogenicity against omicron variants of the fourth dose were evaluated in group A. Participants 60 years and older were involved in group B for safety observations. The primary outcome was geometric mean titres (GMTs) of the neutralising antibodies against omicron and seroconversion rates against BA.5 variant 28 days after the boosting, and incidence of adverse reactions within 28 days. The intention-to-treat group was involved in the safety analysis, while all patients in group A who had blood samples taken before and after the booster were involved in the immunogenicity analysis. This trial was registered at the Chinese Clinical Trial Registry Centre (ChiCTR2200064575).

FINDINGS

Between Oct 13, and Nov 22, 2022, 320 participants were enrolled in group A (240 in the CS-2034 group and 80 in the BBIBP-CorV group) and 113 in group B. Adverse reactions after vaccination were more frequent in CS-2034 recipients (158 [44·8%]) than BBIBP-CorV recipients (17 [21·3%], p<0·0001). However, most adverse reactions were mild or moderate, with grade 3 adverse reactions only reported by eight (2%) of 353 participants receiving CS-2034. Heterologous boosting with CS-2034 elicited 14·4-fold (GMT 229·3, 95% CI 202·7-259·4 vs 15·9, 13·1-19·4) higher concentration of neutralising antibodies to SARS-CoV-2 omicron variant BA.5 than did homologous boosting with BBIBP-CorV. The seroconversion rates of SARS-CoV-2-specific neutralising antibody responses were much higher in the mRNA heterologous booster regimen compared with BBIBP-CorV homologous booster regimen (original strain 47 [100%] of 47 vs three [18·8%] of 16; BA.1 45 [95·8%] of 48 vs two [12·5%] 16; and BA.5 233 [98·3%] of 240 vs 15 [18·8%] of 80 by day 28).

INTERPRETATION

Both the administration of mRNA vaccine CS-2034 and inactivated vaccine BBIBP-CorV as a fourth dose were well tolerated. Heterologous boosting with mRNA vaccine CS-2034 induced higher immune responses and protection against symptomatic SARS-CoV-2 omicron infections compared with homologous boosting, which could support the emergency use authorisation of CS-2034 in adults.

FUNDING

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

TRANSLATION

For the Chinese translation of the abstract see Supplementary Materials section.

SARS-CoV-2 Vaccine Uptake among Patients with Chronic Liver Disease: A Cross-Sectional Analysis in Hebei Province, China

Chronic liver disease (CLD) patients have higher mortality and hospitalization rates after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This study aimed to explore SARS-CoV-2 vaccine perceptions, side effects, factors associated with nonvaccination and attitudes toward fourth-dose vaccine among CLD patients. The differences between vaccinated and unvaccinated groups among 1491 CLD patients and the risk factors associated with nonvaccination status were analyzed. In total, 1239 CLD patients were immunized against SARS-CoV-2. CLD patients have a high level of trust in the government and clinicians and were likely to follow their recommendations for vaccination. Reasons reported for nonvaccination were mainly concerns about the vaccines affecting their ongoing treatments and the fear of adverse events. However, only 4.84% of patients reported mild side effects. Risk factors influencing nonvaccination included being older in age, having cirrhosis, receiving treatments, having no knowledge of SARS-CoV-2 vaccine considerations and not receiving doctors' positive advice on vaccination. Furthermore, 20.6% of completely vaccinated participants refused the fourth dose because they were concerned about side effects and believed that the complete vaccine was sufficiently protective. Our study proved that SARS-CoV-2 vaccines were safe for CLD patients. Our findings suggest that governments and health workers should provide more SARS-CoV-2 vaccination information and customize strategies to improve vaccination coverage and enhance vaccine protection among the CLD population.

Characterization of immune responses to two and three doses of the adenoviral vectored vaccine ChAdOx1 nCov-19 and the whole virion inactivated vaccine BBV152 in a mix-and-match study in India

Infections with SARS-CoV-2 variants and declining immunity after primary vaccination, encouraged the use of booster doses. Some countries changed their immunization programmes to boost with vaccines different from the ones in their original schedule, based on results from immunogenicity and effectiveness studies. This study reports immunological analysis of samples collected in a phase 4 randomized trial, where participants who had previously received two primary doses of ChAdOx1 nCov-19 (ChAd) or inactivated BBV152 vaccine were randomized to receive either ChAd or BBV152 booster and further categorized as: Group 1 (two primary doses of ChAd - ChAd booster), Group 2 (two primary doses of ChAd - BBV152 booster), Group 3 (two primary doses of BBV152 - ChAd booster), and Group 4 (two primary doses of BBV152 - BBV152 booster). SARS-CoV-2 specific cellular and humoral responses at day 0 (pre-boost samples 12-36 weeks after the second primary dose), and at day 28 post booster, were measured in a subset of participants (ChAd recipients, n = 37 and BBV152 recipients, n = 36). Additionally, on day180 post-booster humoral responses were assessed for the entire cohort (N = 378). Primary vaccination with 2 doses of BBV152 generated higher memory-B cells (median% 0.41 vs 0.35) and cytokine producing CD8-Tcells (median% 0.09 vs 0.04) while lower anti-spike IgG levels (medianAU/ml: 12,433 vs 27,074) as compared to ChAd. Irrespective of the primary vaccine received, ChAd boosted individuals generated higher memory-B cell frequencies and anti-spike IgG levels as compared to BBV152 booster. The percentage ACE-2 inhibition against Omicron and its sub-variants was higher in Group 3 (median > 60 %) as compared to other groups (median < 25 %). At day180 post booster the hierarchy of the antibody amounts was Group 1 ∼ Group 2 ∼ Group 3 > Group 4. Sustained humoral and robust cellular immune response to SARS-CoV-2 can be obtained with ChAd booster irrespective of the primary vaccination regimen. The trial is registered with ISRTCN (CTRI/2021/08/035648).

Immunological responses and adverse reactions of the heterologous second booster dose of BNT162b2 after two-dose CoronaVac for COVID-19 vaccination in healthcare workers of Faculty of Medicine, Naresuan University

BACKGROUND

The first COVID-19 vaccination campaign in Thailand began in April 2020, with healthcare workers receiving two doses of inactivated COVID-19 vaccine (CoronaVac). However, the emergence of the delta and omicron variants raised concerns about vaccine effectiveness. The Thai Ministry of Public Health provided the first booster dose (third dose) and second booster dose (fourth dose) of the mRNA vaccine (BNT162b2) for healthcare workers. This study investigated the immunity and adverse reactions elicited by a heterologous second booster dose of BNT162b2 after a two-dose CoronaVac vaccination for COVID-19 in healthcare workers of the Faculty of Medicine, Naresuan University.

METHODS

IgG titres against the SARS-CoV-2-spike protein were measured four and 24 weeks after the second booster dose of BNT162b2 in the study participants. Adverse reactions were recorded during the first three days, four weeks and 24 weeks after the second booster dose of BNT162b2.

RESULTS

IgG against the SARS-CoV-2-spike protein was positive (>10 U/ml) in 246 of 247 participants (99.6 %) at both four and 24 weeks after the second booster dose of BNT162b2. The median specific IgG titres at four and 24 weeks after the second booster dose of BNT162b2 were 299 U/ml (min: 2, max: 29,161) and 104 U/ml (min: 1, max: 17,920), respectively. The median IgG level declined significantly 24 weeks after the second booster dose of the BNT162b2 vaccine. Of the 247 participants, 179 (72.5 %) experienced adverse reactions in the first three days after the second booster dose of BNT162b2. Myalgia, fever, headache, injection site pain and fatigue were the most common adverse reactions.

CONCLUSION

This study demonstrated that a heterologous second booster dose of BNT162b2 after two doses of CoronaVac induced elevated IgG against the SARS-CoV-2-spike protein and caused minor adverse reactions in healthcare workers of the Faculty of Medicine, Naresuan University. This study was registered as Thailand Clinical Trials No. TCTR20221112001.

Third COVID-19 vaccine dose for people with multiple sclerosis who did not seroconvert following two doses of BBIBP-CorV (Sinopharm) inactivated vaccine: A pilot study on safety and immunogenicity

Background

People with multiple sclerosis (pwMS) on anti-CD20 therapies (aCD20) and fingolimod have shown inadequate humoral responses to COVID-19 vaccines.

Objective

The objective of the study was to pilot larger studies by demonstrating the safety and comparing the immunogenicity of different types of third doses in seronegative pwMS after two doses of BBIBP-CorV inactivated vaccine.

Methods

In December 2021, subject to receiving their third dose, being COVID-19-naiive, and receiving no corticosteroid within two months, we measured the level of anti-SARS-CoV-2-Spike IgG in pwMS seronegative after two shots of BBIBP-CorV inactivated vaccine.

Results

We included 20/29 pwMS who received adenoviral vector (AV), 7/29 who received inactivated, and 2/29 who received conjugated third doses. No serious adverse events were reported two weeks post-third dose. The pwMS receiving AV third doses showed significantly increased IgG concentrations, while only the ones not on aCD20 and fingolimod responded to inactivated third doses. An ordinal logistic multivariable generalized linear model indicated that age (per year β: -0.10, P = 0.04), type of disease-modifying therapy (aCD20 β: -8.36, P <0.01; fingolimod β: -8.63, P = 0.01; others: reference), and type of third dose (AV or conjugated β: 2.36, P = 0.02; inactivated: reference) are predictive of third dose immunogenicity among pwMS who remain seronegative after two shots of BBIBP-CorV vaccine. Statistical significance was not achieved for variables sex, MS duration, EDSS, duration of DMT, duration of third dose to IgG test, and duration from last aCD20 infusion to third dose.

Conclusion

This preliminary pilot study highlights the need for further research to determine the optimal COVID-19 third dose vaccination strategy for pwMS living in areas where BBIBP-CorV vaccine has been used.

Safety and immunogenicity of a third dose of COVID-19 protein subunit vaccine (CovovaxTM) after homologous and heterologous two-dose regimens

OBJECTIVES

To report the safety and immunogenicity profile of a protein subunit vaccine (Covovax^TM) given as a third (booster) dose to individuals primed with different primary vaccine regimens.

METHODS

A third dose was administered to individuals with an interval range of 3-10 months after the second dose. The four groups were classified according to their primary vaccine regimens, including two-dose BBIBP-CorV, AZD1222, BNT162b2, and CoronaVac/AZD1222. Immunogenicity analysis was performed to determine binding antibodies, neutralizing activity, and the T-cell responses.

RESULTS

Overall, 210 individuals were enrolled and boosted with the Covovax^TM vaccine. The reactogenicity was mild to moderate. Most participants elicited a high level of binding and neutralizing antibody against Wild-type and Omicron variants after the booster dose. In participants who were antinucleocapsid immunoglobulin G-negative from all groups, a booster dose could elicit neutralizing activity to Wild-type and Omicron variants by more than 95% and 70% inhibition at 28 days, respectively. The Covovax^TM vaccine could elicit a cell-mediated immune response.

CONCLUSION

The protein subunit vaccine (Covovax^TM) can be proposed as a booster dose after two different priming dose regimens. It has strong immunogenicity and good safety profiles.

Expert review of global real-world data on COVID-19 vaccine booster effectiveness and safety during the omicron-dominant phase of the pandemic

INTRODUCTION

COVID-19 vaccines have been highly effective in reducing morbidity and mortality during the pandemic. However, the emergence of the Omicron variant and subvariants as the globally dominant strains have raised doubts about the effectiveness of currently available vaccines and prompted debate about potential future vaccination strategies.

AREAS COVERED

Using the publicly available IVAC VIEW-hub platform, we reviewed 52 studies on vaccine effectiveness (VE) after booster vaccinations. VE were reported for SARS-CoV-2 symptomatic infection, severe disease and death and stratified by vaccine schedule and age. In addition, a non-systematic literature review of safety was performed to identify single or multi-country studies investigating adverse event rates for at least two of the currently available COVID-19 vaccines.

EXPERT OPINION

Booster shots of the current COVID-19 vaccines provide consistently high protection against Omicron-related severe disease and death. Additionally, this protection appears to be conserved for at least 3 months, with a small but significant waning after that. The positive risk-benefit ratio of these vaccines is well established, giving us confidence to administer additional doses as required. Future vaccination strategies will likely include a combination of schedules based on risk profile, as overly frequent boosting may be neither beneficial nor sustainable for the general population.

Effectiveness of ChAdOx1-S COVID-19 booster vaccination against the Omicron and Delta variants in England

Despite the availability of the ChAdOx1-S booster vaccine, little is known about the real-world effectiveness although clinical trials have demonstrated enhanced immunity following a ChAdOx1-S booster. In England 43,171 individuals received a ChAdOx1-S booster whilst 13,038,908 individuals received BNT162b2 in the same period. ChAdOx1-S booster recipients were more likely to be female (adjusted odds ratio (OR) 1.67 (1.64-1.71)), in a clinical risk group (adjusted OR 1.58 (1.54-1.63)), in the clinically extremely vulnerable group (adjusted OR 1.84 (1.79-1.89)) or severely immunosuppressed (adjusted OR 2.05 (1.96-2.13)). The effectiveness of the ChAdOx1-S and BNT162b2 boosters is estimated here using a test-negative case-control study. Protection against symptomatic disease with the Omicron variant peaks at 66.1% (16.6 to 86.3%) and 68.5% (65.7 to 71.2%) for the ChAdOx1-S and BNT162b2 boosters in older adults. Protection against hospitalisation peaks at 82.3% (64.2 to 91.3%) and 90.9% (88.7 to 92.7%). For Delta, effectiveness against hospitalisation is 80.9% (15.6% to 95.7%) and 93.9% (92.8% to 94.9%) after ChAdOx1-S and BNT162b2 booster vaccination. This study supports the consideration of ChAdOx1-S booster vaccination for protection against severe COVID-19 in settings yet to offer boosters and suggests that individuals who received a ChAdOx1-S booster do not require re-vaccination ahead of others.

COVID-19 Vaccines, Effectiveness, and Immune Responses

The COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has captivated the globe's attention since its emergence in 2019. This highly infectious, spreadable, and dangerous pathogen has caused health, social, and economic crises. Therefore, a worldwide collaborative effort was made to find an efficient strategy to overcome and develop vaccines. The new vaccines provide an effective immune response that safeguards the community from the virus' severity. WHO has approved nine vaccines for emergency use based on safety and efficacy data collected from various conducted clinical trials. Herein, we review the safety and effectiveness of the WHO-approved COVID-19 vaccines and associated immune responses, and their impact on improving the public's health. Several immunological studies have demonstrated that vaccination dramatically enhances the immune response and reduces the likelihood of future infections in previously infected individuals. However, the type of vaccination and individual health status can significantly affect immune responses. Exposure of healthy individuals to adenovirus vectors or mRNA vaccines causes the early production of antibodies from B and T cells. On the other hand, unhealthy individuals were more likely to experience harmful events due to relapses in their existing conditions. Taken together, aligning with the proper vaccination to a patient's case can result in better outcomes.

Immunogenicity, durability, and safety of an mRNA and three platform-based COVID-19 vaccines as a third dose following two doses of CoronaVac in China: A randomised, double-blinded, placebo-controlled, phase 2 trial

BACKGROUND

More effective vaccine candidates against variants of concern as a booster dose are needed in people primed with two-dose inactivated COVID-19 vaccines.

METHODS

This randomised, double-blinded, investigator-initiated phase 2 trial aims to evaluate immunogenicity, durability, and safety of an mRNA vaccine candidate (RQ3013) and three other platform vaccines (an adenovirus-vectored vaccine candidate [ChAdTS-S], a recombinant protein vaccine candidate [ZR202-CoV], and an inactivated vaccine [CoronaVac]) as a booster. 250 eligible volunteers, who had received a prime two-dose CoronaVac (3 to 5 weeks apart) vaccination 100-270 days before, were randomly assigned in a 1:1:1:1:1 ratio to receive a third dose of RQ3013 (30 μg mRNA per 0.15 mL), ChAdTS-S (5×10¹⁰ viral particles per 0.5 mL), ZR202-CoV (25 μg prefusion-stabilized Spike ectodomain trimer per 0.5 mL), CoronaVac (3 μg inactivated CN02 strain of SARS-CoV-2 per 0.5 mL) or placebo (0.5 mL of 0.9% sodium chloride solution) via intramuscular injection into the upper arm at a single clinical site in Kunming, China. Participants, investigators, and immunogenicity laboratory were masked to group assignment. The primary immunogenicity outcomes were geometric mean titres (GMTs) of neutralising antibodies against live SARS-CoV-2 (wild-type, delta and omicron) virus at day 0 (before vaccination), day 7, day 14 and day 28 after vaccination, as analysed in a modified intention-to-treat (mITT) population (all participants who completed their booster doses and had at least one post-dose immunogenicity data). Secondary outcomes include T cell responses against the wild-type and omicron SARS-CoV-2 Spike protein. The primary safety outcome was incidence of adverse events within 14 days after the booster vaccination. This trial is registered with ChiCTR.org.cn, ChiCTR2200057758.

FINDINGS

Between January 1, 2022, and February 28, 2022, 235 eligible participants were enrolled and vaccinated, and the primary analysis included 234 participants. At baseline, neutralising antibodies against wild-type virus, the delta, or omicron variants were low or undetectable in all groups. After the booster vaccination, GMTs of neutralising antibodies ranged from 75.4 (95% confidence interval [CI] 61.4-92.5) in CoronaVac to 950.1 (95% CI 785.4-1149.3) in RQ3013 against live wild-type SARS-CoV-2, and from 8.1 (95% CI: 6.1-10.7) in CoronaVac to 247.0 (95% CI 194.1-314.3) in RQ3013 against the omicron variant at day 14. Immunogenicities of all heterologous regimens were superior to that of homologous regimen in neutralisation against all tested SARS-CoV-2 strains, with RQ3013 showing the highest geometric mean ratios (GMRs) of 12.6, 14.7, and 31.3 against the wild-type, the delta variant and the omicron variant compared to CoronaVac at day 14 post-vaccination, respectively. Durability analysis at day 90 showed that >90% of participants in RQ3013 and ZR202-CoV were seropositive for the omicron variant while ZR202-CoV with adjuvants containing CpG showed a slightly better durability than RQ3013. T cell responses specific to the omicron variant were similar to that of the wild-type, with RQ3013 showing the highest boosting effect. Any solicited injection site or systemic adverse events reported within 14 days after vaccination were most commonly observed in RQ3013 (47/47, 100%), followed by ZR202-CoV (46/47, 97.9%) and ChAdTS-S (43/48, 89.6%), and then CoronaVac (37/46, 80.4%) and placebo (21/47, 44.7%). More than 90% of the adverse events were grade 1 (mild) or 2 (moderate) with a typical resolution time of 3 days. No grade 4 adverse events or serious adverse events were reported by study vaccines.

INTERPRETATION

Although all study vaccines boosted neutralising antibodies with no safety concerns, RQ3013 showed much stronger cross-neutralisation and cellular responses, adding more effective vaccine candidates against the omicron variant.

FUNDING

Yunnan Provincial Science and Technology Department China (202102AA100051 and 202003AC100010), the Double First-class University funding to Yunnan University, National Natural Science Foundation of China (81960116, 82060368 and 82170711), Yunnan Natural Science Foundation (202001AT070085), High-level Health Technical Personnel Project of Yunnan Province (H-2018102) and Spring City Plan: The High-level Talent Promotion and Training Project of Kunming.

Reactogenicity, immunogenicity, and humoral immune response dynamics after the third dose of heterologous COVID-19 vaccines in participants fully vaccinated with inactivated vaccine

INTRODUCTION

Immunogenicity after the CoronaVac vaccine remains uncertain, especially regarding infections with the coronavirus variants of concern and waning immunity.

METHODS

This was a single-center, open-label clinical trial designed to assess the immunogenicity and safety of BBIBP-CorV, AZD1222, or BNT162b2 as the third vaccination. The key eligible criteria were individuals at least 18 years old who were fully vaccinated with two doses of CoronaVac vaccine for 2-4 months. The primary endpoint was the ratio of the geometric mean concentration (GMC) of the total anti-receptor binding domain (RBD) antibody post-vaccination compared with that pre-vaccination. The secondary endpoint was reactogenicity within 7 days.

RESULTS

Forty-one participants received AZD1222, 40 received BBIBP-CorV, and 40 received BNT162b2. The GMC of anti-RBD antibody at 2 weeks post-vaccination was 31,138.67 binding antibody units (BAU)/mL for BNT162b2, 6,412.10 BAU/mL for AZD1222, and 1,092.7 BAU/mL for BBIBP-CorV. Compared with pre-vaccination, the ratio of anti-RBD concentration was 690.24 for BNT162b2, 130.02 for AZD1222, and 17.79 for BBIBP-CorV. No potentially life-threatening adverse reaction were observed within 7 days.

CONCLUSION

A third vaccination with the heterologous vaccine, BBIBP-CorV, AZD1222, or BNT162b2, can elicit a robust immune response, without serious adverse events in participants fully vaccinated with the CoronaVac vaccine.

Preceding anti-spike IgG levels predicted risk and severity of COVID-19 during the Omicron-dominant wave in Santa Fe city, Argentina

The SARS-CoV-2 Omicron variant has increased infectivity and immune escape compared with previous variants, and caused the surge of massive COVID-19 waves globally. Despite a vast majority (~90%) of the population of Santa Fe city, Argentina had been vaccinated and/or had been infected by SARS-CoV-2 when Omicron emerged, the epidemic wave that followed its arrival was by far the largest one experienced in the city. A serosurvey conducted prior to the arrival of Omicron allowed to assess the acquired humoral defences preceding the wave and to conduct a longitudinal study to provide individual-level real-world data linking antibody levels and protection against COVID-19 during the wave. A very large proportion of 1455 sampled individuals had immunological memory against COVID-19 at the arrival of Omicron (almost 90%), and about half (48.9%) had high anti-spike immunoglobulin G levels (>200 UI/ml). However, the antibody titres varied greatly among the participants, and such variability depended mainly on the vaccine platform received, on having had COVID-19 previously and on the number of days elapsed since last antigen exposure (vaccine shot or natural infection). A follow-up of 514 participants provided real-world evidence of antibody-mediated protection against COVID-19 during a period of high risk of exposure to an immune-escaping highly transmissible variant. Pre-wave antibody titres were strongly negatively associated with COVID-19 incidence and severity of symptoms during the wave. Also, receiving a vaccine shot during the follow-up period reduced the COVID-19 risk drastically (15-fold). These results highlight the importance of maintaining high defences through vaccination at times of high risk of exposure to immune-escaping variants.

The immunogenicity of an inactivated vaccine against SARS-CoV-2 in healthy individuals: A systematic review and meta-analysis

OBJECTIVE

Inactivated (killed) vaccines against COVID-19 have been widely used for the control of the pandemic condition. We performed a systematic and meta-analysis review of randomized, double-blind, placebo-controlled trials of the immunogenicity of inactivated vaccines against SARS-CoV-2 in healthy individuals.

METHODS

In the present study, all research and evidence were extracted from the available online databases. Two researchers randomly evaluated the assessment of the research sensitivity. Finally, after quality assessment and regarding the specific inclusion and exclusion criteria, the eligible articles were entered for meta-analysis. The heterogeneity between the results of the studies was measured using test statistics (Cochran's Q) and the I² index. The forest plots illustrated the point and pooled estimates with 95% confidence intervals (crossed lines). All statistical analyses were performed using Comprehensive meta-Analysis V.2 software.

RESULTS

This meta-analysis included six primary studies investigating the immunogenicity of inactivated vaccines against SARS-CoV-2 in healthy individuals. According to the pooled prevalence (95% confidence interval), neutralizing antibody responses 28 days after receiving the second dose regarding different ages and micrograms per dose was 95.50% (CI: 93.2-97.1%). Our results showed that antibody levels were higher in the 6 μg group than in other groups. 98.3% (CI: 94.2-99.5%).

CONCLUSION

Since the rapid development of vaccinations has sparked widespread public anxiety regarding vaccine efficacy. Governments and unvaccinated individuals, particularly those with vaccination reluctance, will be interested in and benefit from the findings of this systematic study.

Cost-Effectiveness of COVID-19 Sequential Vaccination Strategies in Inactivated Vaccinated Individuals in China

To effectively prevent and control the COVID-19 pandemic, countries have adopted a booster vaccination strategy. This study aimed to estimate the cost-effectiveness of sequential booster COVID-19 vaccination compared to two-dose inactivated vaccination in China from a societal perspective. A Markov model was developed to estimate the cost-effectiveness of sequential vaccination, including two doses of an inactivated vaccine followed by a booster shot of an inactivated vaccine, adenovirus vectored vaccine, protein subunit vaccine, or mRNA vaccine. The incremental effects of a booster shot with an inactivated vaccine, protein subunit vaccine, adenovirus vectored vaccine, and mRNA vaccine were 0.0075, 0.0110, 0.0208, and 0.0249 QALYs and saved costs of US$163.96, US$261.73, US$583.21, and US$724.49, respectively. Under the Omicron virus pandemic, the sequential vaccination among adults and the elderly (aged 60-69, 70-79, over 80) was consistently cost-saving, and a booster shot of the mRNA vaccine was more cost-saving. The results indicate that the sequential vaccination strategy is cost-effective in addressing the COVID-19 pandemic, and improving vaccination coverage among the elderly is of great importance in avoiding severe cases and deaths.

Fast-track development of vaccines for SARS-CoV-2: The shots that saved the world

In December 2019, an outbreak emerged of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which leads to coronavirus disease 2019 (COVID-19). The World Health Organisation announced the outbreak a global health emergency on 30 January 2020 and by 11 March 2020 it was declared a pandemic. The spread and severity of the outbreak took a heavy toll and overburdening of the global health system, particularly since there were no available drugs against SARS-CoV-2. With an immediate worldwide effort, communication, and sharing of data, large amounts of funding, researchers and pharmaceutical companies immediately fast-tracked vaccine development in order to prevent severe disease, hospitalizations and death. A number of vaccines were quickly approved for emergency use, and worldwide vaccination rollouts were immediately put in place. However, due to several individuals being hesitant to vaccinations and many poorer countries not having access to vaccines, multiple SARS-CoV-2 variants quickly emerged that were distinct from the original variant. Uncertainties related to the effectiveness of the various vaccines against the new variants as well as vaccine specific-side effects have remained a concern. Despite these uncertainties, fast-track vaccine approval, manufacturing at large scale, and the effective distribution of COVID-19 vaccines remain the topmost priorities around the world. Unprecedented efforts made by vaccine developers/researchers as well as healthcare staff, played a major role in distributing vaccine shots that provided protection and/or reduced disease severity, and deaths, even with the delta and omicron variants. Fortunately, even for those who become infected, vaccination appears to protect against major disease, hospitalisation, and fatality from COVID-19. Herein, we analyse ongoing vaccination studies and vaccine platforms that have saved many deaths from the pandemic.

Persistence of immunity against Omicron BA.1 and BA.2 variants following homologous and heterologous COVID-19 booster vaccines in healthy adults after a two-dose AZD1222 vaccination

OBJECTIVES

The SARS-CoV-2 Omicron variant presents numerous mutations potentially able to evade neutralizing antibodies (NAbs) elicited by COVID-19 vaccines. Therefore, this study aimed to provide evidence on a heterologous booster strategy to overcome the waning immunity against Omicron variants.

METHODS

Participants who completed the Oxford/AstraZeneca (hereafter AZD1222) vaccine dose for 5-7 months were enrolled. The reactogenicity and persistence of immunogenicity in both humoral and cellular response after a homologous or heterologous booster with the AZD1222 and messenger RNA (mRNA) vaccines (BNT162b2, full, or half-dose mRNA-1273) administered 6 months after primary vaccination were determined.

RESULTS

A total of 229 individuals enrolled, and waning of immunity was observed 5-7 months after the AZD1222-primed vaccinations. Total receptor-binding domain (RBD) immunoglobulin (Ig) levels, anti-RBD IgG, and focus reduction neutralization test against Omicron BA.1 and BA.2 variants and T cell response peaked at 14-28 days after booster vaccination. Both the full and half dose of mRNA-1273 induced the highest response, followed by BNT162b2 and AZD1222. At 90 days, the persistence of immunogenicity was observed among all mRNA-boosted individuals. Adverse events were acceptable for all vaccines.

CONCLUSION

A heterologous mRNA booster provided a significantly superior boost of binding and NAbs levels against the Omicron variant compared with a homologous booster in individuals with AZD1222-primed vaccinations.

Multiple sclerosis disease-modifying therapies and COVID-19 vaccines: a practical review and meta-analysis

Studies among people with multiple sclerosis (pwMS) receiving disease-modifying therapies (DMTs) have provided adequate evidence for an appraisal of COVID-19 vaccination policies among them. To synthesise the available evidence addressing the effect of MS DMTs on COVID-19 vaccines' immunogenicity and effectiveness, following the Cochrane guidelines, we systematically reviewed all observational studies available in MEDLINE, Scopus, Web of Science, MedRxiv and Google Scholar from January 2021 to January 2022 and extracted their relevant data. Immunogenicity data were then synthesised in a quantitative, and other data in a qualitative manner. Evidence from 28 studies suggests extensively lower B-cell responses in sphingosine-1-phosphate receptor modulator (S1PRM) treated and anti-CD20 (aCD20) treated, and lower T-cell responses in interferon-treated, S1PRM-treated and cladribine-treated pwMS-although most T cell evidence currently comprises of low or very low certainty. With every 10-week increase in aCD20-to-vaccine period, a 1.94-fold (95% CI 1.57 to 2.41, p<0.00001) increase in the odds of seroconversion was observed. Furthermore, the evidence points out that B-cell-depleting therapies may accelerate postvaccination humoral waning, and boosters' immunogenicity is predictable with the same factors affecting the initial vaccination cycle. Four real-world studies further indicate that the comparative incidence/severity of breakthrough COVID-19 has been higher among the pwMS treated with S1PRM and aCD20-unlike the ones treated with other DMTs. S1PRM and aCD20 therapies were the only DMTs reducing the real-world effectiveness of COVID-19 vaccination among pwMS. Hence, it could be concluded that optimisation of humoral immunogenicity and ensuring its durability are the necessities of an effective COVID-19 vaccination policy among pwMS who receive DMTs.

Comparison of the reactogenicity and immunogenicity of a reduced and standard booster dose of the mRNA COVID-19 vaccine in healthy adults after two doses of inactivated vaccine

The coronavirus disease 2019 (COVID-19) pandemic has been a serious healthcare problem worldwide since December 2019. The third dose of heterologous vaccine was recently approved by World Health Organization. The present study compared the reactogenicity and immunogenicity of the reduced and standard third booster dose of the BNT162b2 and mRNA-1273 vaccine in adults who previously received the two-dose CoronaVac vaccine. Results showed that headache, joint pain, and diarrhea were more frequent in the 15 μg- than the 30 μg-BNT162b2 groups, whereas joint pain and chilling were more frequent in the 100 μg- than the 50 μg-mRNA-1273 groups. No significant differences in immunogenicity were detected. These findings demonstrate that the reduced dose of the mRNA vaccines elicited antibody responses against the SARS-CoV-2 delta and omicron variants that were comparable to the standard dose. The reduced dose could be used to increase vaccine coverage in situations of limited global vaccine supply.

Safety and Humoral and Cellular Immunogenicity of the BNT162b2 SARS-CoV-2 Vaccine in Liver-Transplanted Adolescents Compared to Healthy Adolescents

Since BNT162b2 was approved to prevent COVID-19 in children, we aim to compare the safety and immunogenicity of the BNT162b2 vaccine in liver-transplanted (LT) and healthy adolescents. LT and healthy adolescents received two doses of 30 µg of BNT162b2. All were evaluated for total COVID-19 antibodies directed against the receptor-binding domain (RBD) and interferon-γ using the ELISpot at all time points; anti-nucleocapsid immunoglobulin was evaluated at week 8 and the surrogate virus-neutralizing antibody (sVN) to Omicron at day 0 and week 8. Adverse effects were recorded during days 0−7. In total, 16 LT and 27 healthy adolescents were enrolled (aged 14.78 ± 1.70 years). After completion, all LT and healthy adolescents were positive for anti-RBD immunoglobulin, with geometric mean titers of 1511.37 (95% CI 720.22−3171.59) and 6311.90 (95% CI 4955.46−8039.64)) U/mL (p < 0.001). All tested negative for anti-nucleocapsid immunoglobulin, indicating no COVID-19 infection after vaccination. However, the sVNs to Omicron were positive in only nine (33.33%) healthy adolescents and none of the LT adolescents. Interferon-γ-secreting cells were lower in LT adolescents than healthy adolescents. The LT adolescents had a lower immunogenic response to BNT162b2 than the healthy adolescents. Administrating two doses of BNT162b2 was safe, but was less effective against the Omicron variant.

Real-World Effectiveness of Mix-and-Match Vaccine Regimens against SARS-CoV-2 Delta Variant in Thailand: A Nationwide Test-Negative Matched Case-Control Study

The objective of this study is to explore the real-world effectiveness of various vaccine regimens to tackle the epidemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant in Thailand during September–December 2021. We applied a test-negative case control study, using nationwide records of people tested for SARS-CoV-2. Each case was matched with two controls with respect to age, detection date, and specimen collection site. A conditional logistic regression was performed. Results were presented in the form vaccine effectiveness (VE) and 95% confidence interval. A total of 1,460,458 observations were analyzed. Overall, the two-dose heterologous prime-boost, ChAdOx1 + BNT162b2 and CoronaVac + BNT162b2, manifested the largest protection level (79.9% (74.0–84.5%) and 74.7% (62.8–82.8%)) and remained stable over the whole study course. The three-dose schedules (CoronaVac + CoronaVac + ChAdOx1, and CoronaVac + CoronaVac + BNT162b2) expressed very high degree of VE estimate (above 80.0% at any time interval). Concerning severe infection, almost all regimens displayed very high VE estimate. For the two-dose schedules, heterologous prime-boost regimens seemed to have slightly better protection for severe infection relative to homologous regimens. Campaigns to expedite the rollout of third-dose booster shot should be carried out. Heterologous prime-boost regimens should be considered as an option to enhance protection for the entire population.

Immunogenicity of the third and fourth BNT162b2 mRNA COVID-19 boosters and factors associated with immune response in patients with SLE and rheumatoid arthritis

Objectives

To evaluate the safety and immunogenicity of third and fourth BNT162b2 boosters in patients with SLE and rheumatoid arthritis (RA).

Methods

Patients with SLE and RA aged 18–65 years who completed a series of inactivated, adenoviral vector, or heterogenous adenoviral vector/mRNA vaccines for at least 28 days were enrolled. Immunogenicity assessment was done before and day 15 after each booster vaccination. The third BNT162b2 booster was administered on day 1. Patients with suboptimal humoral response to the third booster dose (antireceptor-binding domain (RBD) IgG on day 15 <2360 BAU/mL) were given a fourth BNT162b2 booster on day 22.

Results

Seventy-one patients with SLE and 29 patients with RA were enrolled. The third booster raised anti-RBD IgG by 15-fold, and patients with positive neutralising activity against the Omicron variant increased from 0% to 42%. Patients with positive cellular immune response also increased from 55% to 94%. High immunosuppressive load and initial inactivated vaccine were associated with lower anti-RBD IgG titre. Fifty-four patients had suboptimal humoral responses to the third booster and 28 received a fourth booster dose. Although anti-RBD IgG increased further by sevenfold, no significant change in neutralising activity against the Omicron variant was observed. There were two severe SLE flares that occurred shortly after the fourth booster dose.

Conclusions

The third BNT162b2 booster significantly improved humoral and cellular immunogenicity in patients with SLE and RA. The benefit of a short-interval fourth booster in patients with suboptimal humoral response was unclear.

Trial registration number

TCTR20211220004.

Protocol of an Exploratory Single-Arm Study to Evaluate the Safety and Immunogenicity of KD-414 as a Booster Vaccine for SARS-CoV-2 in Healthy Adults (KAPIVARA)

Background: The coronavirus disease 2019 (COVID-19) pandemic is currently ongoing, and there have been significant efforts in the development of COVID-19 vaccines. However, the neutralizing antibody titers in vaccinated individuals are reported to progressively decrease over time. Japanese pharmaceutical companies have published the results of Phase I and II studies on the safety and efficacy of different vaccines. Final clinical trials will be conducted with the aim of practical application by March 2023. To effectively utilize vaccines developed by Japanese companies, the efficacy and safety of a booster dose (i.e., third vaccination) must be evaluated among individuals who have received three doses of different vaccines. Methods: This protocol describes a study that aims to examine the effect of a booster dose of “KD-414”, a novel Japanese inactivated vaccine, on antibody titers among participants involved in a previous study. Volunteers in this protocol will be recruited from participants in the previous study and immunized with KD-414 after obtaining consent. The antibody titers, before and after immunization with KD-414, among participants who previously received two doses of the BNT162b2 mRNA vaccine, will be comparatively analyzed. Discussion: The reactogenicity and immunogenicity of seven different COVID-19 vaccines including an inactivated vaccine as a third dose after two doses of ChAdOx1 nCov-19 or BNT162b2, has been tested previously, and found to be superior to control (quadrivalent meningococcal conjugate vaccine) regardless of which vaccine had been received during the initial course. This suggests that many types of third booster doses are efficacious. It is anticipated that this study will provide evidence of the safety and immunogenicity of KD-414 as a booster vaccine, which will have profound public health implications.

A single-center COVID-19 vaccine experience with CoronaVac and BNT162b2 in familial Mediterranean fever patients

Aim

To determine frequency of adverse events and attacks related to vaccination in recipients of CoronaVac and BNT162b2 in familial Mediterranean fever (FMF) patients, and to search whether history of prior COVID‐19 or a booster dose increases occurrence of adverse events/attacks.

Methods

FMF patients were surveyed for administration of any COVID‐19 vaccine and vaccine‐related adverse events or FMF attacks. Demographic, clinical, vaccine‐related data, history of COVID‐19 infection before or after vaccination, adherence to FMF treatment during vaccination were collected.

Results

A total of 161 vaccinated FMF patients were included. Ninety‐three patients out of 161 had reported suffering from an adverse event/attack after a vaccine dose. There were 54.7% of BNT162b2 recipients who reported any adverse event after any vaccine dose in comparison to 29.9% of CoronaVac recipients (P < .001). There were 22.2% of BNT162b2 recipients who reported suffering from a FMF attack within 1 month after vaccination in comparison to 19.4% of CoronaVac recipients (P = .653). When patients with or without adverse event/attack were compared, no significant differences were observed in means of demographics, comorbid diseases, disease duration, total vaccine doses, or treatments adhered to for FMF. Rates of adverse events/attacks were similar between patients with and without prior COVID‐19. In booster recipients, adverse events/attacks were most frequent after the booster dose.

Conclusions

A considerable number of FMF patients suffered from vaccine‐related adverse events/attacks, particularly with BNT162b2. No serious events or mortalities due to vaccination were detected. Demographics, clinical characteristics and prior history of vaccination did not significantly affect these results. We observed an increased rate of adverse events/attacks with booster dose administration.

Kinetics of the Neutralizing and Spike SARS-CoV-2 Antibodies following the Sinovac Inactivated Virus Vaccine Compared to the Pfizer mRNA Vaccine in Singapore

Introduction: We compared the early total spike antibody (S-Ab) and neutralizing antibody (N-Ab) responses to two vaccines. Methods: We studied 96 Pfizer and 34 Sinovac vaccinees over a 14-month period from January 2021 to February 2022. All vaccinees received three doses of one type of vaccine. Antibody levels (Roche Elecsys total S-Ab and the Snibe N-Ab) were tested 10 days after the first dose, 20 days after the second dose, and 20 days after the booster dose. Results: At all time points, the mRNA vaccine generated higher S-Ab and N-Ab responses than the inactivated virus vaccine (S-Ab: first dose 2.48 vs. 0.4 BAU/mL, second dose 2174 vs. 98 BAU/mL, third dose 15,004 vs. 525 BAU/mL; N-Ab: first dose 0.05 vs. 0.02 µg/mL, second dose 3.48 vs. 0.38 µg/mL, third dose 19.8 vs. 0.89 µg/mL). mRNA vaccine recipients had a 6.2/22.2/28.6-fold higher S-Ab and 2.5/9.2/22.2-fold higher N-Ab response than inactivated virus vaccine recipients after the first/second/third inoculations, respectively. Mann–Whitney U analysis confirmed the significant difference in S-Ab and N-Ab titers between vaccination groups at each time point. Conclusions: The mRNA vaccines generated a more robust S-Ab and N-Ab response than the inactivated virus vaccine at all time points after the first, second, and third vaccinations.

Neutralizing antibody and T cell responses against SARS-CoV-2 variants of concern following ChAdOx-1 or BNT162b2 boosting in the elderly previously immunized with CoronaVac vaccine

Background

The existence of SARS-CoV-2 variants of concern (VOCs) in association with evidence of breakthrough infections despite vaccination resulted in the need for vaccine boosting. In elderly individuals, information on the immunogenicity of booster vaccinations is limited. In countries where the CoronaVac inactivated vaccine is the primary vaccine, the appropriate boosting regimen is not clear. Immunologic studies of the effects of booster vaccination against VOCs, particularly Delta and Omicron, following CoronaVac in elderly individuals are helpful for policy makers. In this study, we determined the immune responses against VOCs following ChAdOx-1 or BNT162b2 boosting in elderly individuals previously immunized with CoronaVac.

Results

Before boosting, the median % inhibition of neutralizing antibodies (NAbs) against the wild-type (WT), Alpha, Beta, Delta and Omicron variants in the ChAdOx-1 and BNT162b2 groups was 52.8% vs. 53.4, 36.6% vs. 39.9, 5.2% vs. 13.7, 34.3% vs. 44.9, and 20.8% vs. 18.8%, respectively. After boosting with ChAdOx-1 or BNT162b2, the % inhibition of NAbs were increased to 97.3% vs. 97.4, 94.3% vs. 97.3%, 79.9 vs. 93.7, 95.5% vs. 97.5, and 26.9% vs. 31.9% for WT, Alpha, Beta, Delta and Omicron variants, respectively. Boosting with BNT162b2 induced significantly higher NAb levels than boosting with ChAdOx-1 against the Alpha, Beta and Delta variants but not the WT and Omicron variants. NAb levels against Omicron variant were not significantly different before and after boosting with ChAdOx-1 or BNT162b2. To evaluate T-cell responses, S peptides of the WT, Alpha, Beta and Delta variants were used to stimulate T cells. Upon stimulation, the expression of IL-17A in CD8 T cells was higher in the BNT162b2 group than in the ChAdOx-1 boosting group. However, IFN-γ production in CD4 and CD8 T cells did not significantly differ under all vaccination regimens. The expression of FasL in CD4 T cells, but not CD8 T cells, was higher in the BNT162b2-boosted group.

Conclusion

Boosting with either ChAdOx-1 or BNT162b2 in CoronaVac-primed healthy elderly individuals induced high NAb production against all examined VOCs except Omicron. BNT162b2 stimulated higher NAb and some T-cell responses than ChAdOx-1. Vaccine boosting is, therefore, recommended for elderly individuals previously immunized with CoronaVac.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12979-022-00279-8.

Immunogenicity and Safety of Homologous and Heterologous Prime-Boost Immunization with COVID-19 Vaccine: Systematic Review and Meta-Analysis

A prime-boost strategy of COVID-19 vaccines brings hope to limit the spread of SARS-CoV-2, while the immunogenicity of the vaccines is waning over time. Whether a booster dose of vaccine is needed has become a widely controversial issue. However, no published meta-analysis has focused on the issue. Therefore, this study assessed the immunogenicity and safety of the different combinations of prime-boost vaccinations. Electronic databases including PubMed, the Cochrane Library, Embase, medRxiv, Wanfang and CNKI were used to retrieve the original studies. A total of 28 studies, 9 combinations of prime-boost vaccinations and 5870 subjects were included in the meta-analysis, and random effect models were used to estimate pooled immunogenicity and safety. The immunity against COVID-19 after the prime vaccination waned over time, especially in the populations primed with inactivated vaccines, in which the seropositive rate of antibodies was only 28% (95% CI: 17-40%). Booster vaccination could significantly increase the antibody responses, and heterologous immunization was more effective than homologous immunization (neutralization titers: 1.65 vs. 1.27; anti-RBD IgG: 1.85 vs. 1.15); in particular, the combination of inactivated-mRNA vaccines had the highest antibody responses (neutralization titers: MRAW = 3.64, 95% CI: 3.54-3.74; anti-RBD IgG: 3.73, 95% CI: 3.59-3.87). Moreover, compared with the initial two doses of vaccines, a booster dose did not induce additional or severe adverse events. The administration of the booster dose effectively recalled specific immune responses to SARS-CoV-2 and increased antibody levels, especially in heterologous immunization. Considering the long-term immunogenicity and vaccine equity, we suggest that now, only individuals primed with inactivated vaccines require a booster dose.

Dynamics of Neutralizing Antibody and T-Cell Responses to SARS-CoV-2 and Variants of Concern after Primary Immunization with CoronaVac and Booster with BNT162b2 or ChAdOx1 in Health Care Workers

Inactivated SARS-CoV-2 vaccine (CoronaVac) is commonly used in national immunization programs. However, the immune response significantly declines within a few months. Our study assessed the immune response against SARS-CoV-2 after receiving booster shots of BNT162b2 or ChAdOx1 among health care workers who previously received CoronaVac as their primary immunization. Fifty-six participants who received ChAdOx1 and forty-two participants who received BNT162b2 were enrolled into this study, which evaluated immune responses, including anti-SARS-CoV-2 spike total antibodies (Elecsys®), surrogated viral neutralization test (sVNT) to ancestral strain (cPass™; GenScript), five variants of concern (Alpha, Beta, Gamma, Delta, and Omicron) (Luminex; multiplex sVNT) and the ELISpot with spike (S1 and S2) peptide pool against the ancestral SARS-CoV-2 strain. The samples were analyzed at baseline, 4, and 12 weeks after primary immunization, as well as 4 and 12 weeks after receiving the booster. This study showed a significant increase in anti-SARS-CoV-2 spike total antibodies, sVNT, and T-cell immune response after the booster, including against the Omicron variant. Immune responses rapidly decreased in the booster group at 12 weeks after booster but were still higher than post-primary vaccination. A fourth dose or a second booster should be recommended, particularly in health care workers.

Effect of BTN162b2 and CoronaVac boosters on humoral and cellular immunity of individuals previously fully vaccinated with CoronaVac against SARS-CoV-2: A longitudinal study

Background

It is essential to know about immune response levels after booster doses of the two different types of vaccines, mRNA, and the inactivated, currently used against COVID‐19. For this purpose, we aimed to determine the effects of BNT162b2 (BNT) and CoronaVac (CV) boosters on the humoral and cellular immunity of individuals who had two doses of CV vaccination.

Methods

The study was conducted in three centers (Koc University Hospital, Istanbul University Cerrahpasa Hospital, and Istanbul University, Istanbul Medical School Hospital) in Istanbul, Turkey. Individuals who had been previously immunized with two doses of CV and no history of COVID‐19 were included. The baseline blood samples were collected 3–5 months after the second dose of CV. Follow‐up blood samples were taken 1 and 3 months after administration of third doses of CV, or one dose of BNT boosters. Neutralizing antibody titers were measured by plaque reduction assay. The CD4+ T cell, CD8+ T cell, effector CD4+CD38+CD69+ T cell, and effector CD8+CD38+CD69+ T cell ratios were determined by flow cytometry. The intracellular IFN‐γ and IL‐2 responses were measured by ELISpot assay.

Results

We found a 3.38‐fold increase in neutralizing antibody geometric mean titers (NA GMT, 78.69) 1 month after BNT booster and maintained at the third month (NA GMT, 80). Nevertheless, in the CV booster group, significantly lower NA GMT than BNT after 1 month and 3 months were observed (21.44 and 28.44, respectively) (p < .001). In the ELISpot assay, IL‐2 levels after BNT were higher than baseline and CV booster (p < .001) while IFN‐γ levels were significantly higher than baseline (p < .001). The CD8+CD38+CD69+ and CD4+CD38+CD69+ T cells were stimulated predominantly in the third month of the BNT boosters.

Conclusion

The neutralizing antibody levels after 3 months of the BNT booster were higher than the antibody levels after CV in fully vaccinated individuals. On the contrary, ratio of the effector T cells increased along with greater IFN‐γ activation after BNT booster. By considering the waning immunity, we suggest a new booster dose with BNT for the countries that already had two doses of primary CV regimens.

Safety and Immunogenicity of a Booster Vaccination by CoronaVac or BNT162b2 in Previously Two-Dose Inactivated Virus Vaccinated Individuals with Negative Neutralizing Antibody

COVID-19 has swept across the globe since 2019 and repeated waves of infection have been caused by different variants of the original SARS-CoV-2 (wild type), with the Omicron and Delta variants having dominated recently. Vaccination is among the most important measures in the absence of widespread use of antivirals for prevention of morbidity and mortality. Inactivated virus vaccine has been abundantly used in many countries as the primary two-dose regimen. We aim to study the safety and immunogenicity of CoronaVac (three-dose inactivated virus vaccine) and the BNT162b2 (two-dose inactivated virus vaccine followed by an mRNA vaccine) booster. Both CoronaVac and BNT162b2 boosters are generally safe and have good immunogenicity against the wild type SARS-CoV-2 and the Delta variant with the majority having neutralizing antibodies (NAb) on day 30 and day 90. However, the BNT162b2 booster is associated with a much higher proportion of positive NAb against the Omicron variant. Only 8% of day 30 and day 90 samples post CoronaVac booster have NAb against the Omicron variant. In addition, more BNT162b2 booster recipients are having positive T-cell responses using interferon gamma release assay. In places using inactivated virus vaccine as the primary two-dose scheme, the heterologous mRNA vaccine booster is safe and more immunogenic against the Omicron variant and should be considered as a preferred option during the current outbreak.

More effective vaccines and oral antivirals: Keys for the battle against Omicron

With the rapid roll out of vaccination programs and extraordinary non-pharmaceutical interventions (NPIs) by the government, China has maintained a "dynamic zero-COVID-19" policy over the last two years. However, the global pandemic and immune evasion of Omicron variant poses a huge challenge to China. Currently, about 87.69% of the Chinese population has been vaccinated, most with inactivated vaccines. Although seroepidemiological data on the vaccinated are lacking, published data suggested that even a homologous booster of an inactivated vaccine displayed very limited neutralizing activity against the Omicron variant and that neutralizing activity was significantly lower than that of a heterologous booster or mRNA vaccine alone. A great concern is whether the neutralizing antibodies induced by inactivated vaccines can provide sufficient protection against the Omicron variant since local transmission of the Omicron variant is now occurring in China. The era of extraordinary NPIs by governments and countries to control the transmission of SARS-CoV-2 is going to change. Omicron's immune evasion of neutralizing antibodies induced by current vaccines and the majority of existing therapeutic SARS-CoV-2 monoclonal antibodies (mAbs) suggest an urgent need for more effective vaccines and highly effective oral antivirals, which will be the keys for the battle against Omicron in the future.

Neutralizing Activities against the Omicron Variant after a Heterologous Booster in Healthy Adults Receiving Two Doses of CoronaVac Vaccination

BACKGROUND

The use of an inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine (CoronaVac) against SARS-CoV-2 is implemented worldwide. However, waning immunity and breakthrough infections have been observed. Therefore, we hypothesized that the heterologous booster might improve the protection against the delta and omicron variants.

METHODS

A total of 224 individuals who completed the two-dose CoronaVac for six months were included. We studied reactogenicity and immunogenicity following a heterologous booster with the inactivated vaccine (BBIBP), the viral vector vaccine (AZD1222), and the mRNA vaccine (both BNT162B2 and mRNA-1273). We also determined immunogenicity at 3- and 6-months boosting intervals.

RESULTS

The solicited adverse events (AEs) were mild to moderate and well-tolerated. Total RBD immunoglobulin (Ig), anti-RBD IgG, focus reduction neutralization test (FRNT50) against delta and omicron variants, and T-cell response were highest in the mRNA-1273 group followed by the BNT162b2, AZD1222 and BBIBP groups, respectively. We also witnessed a higher total Ig anti-RBD in the long-interval than in the short-interval groups.

CONCLUSIONS

All four booster vaccines significantly increased binding and neutralizing antibody (NAbs) in individuals immunized with two doses of CoronaVac. The present evidence may benefit vaccine strategies to thwart variants of concern, including the omicron variant.