Antibody response in elderly vaccinated four times with an mRNA anti-COVID-19 vaccine

Immunogenicity of BNT162b2 as a first booster after a ChAdOx1 primary series in a Thai geriatric population living with frailty

OBJECTIVES

Impact of frailty towards immunogenicity and reactogenicity of BNT162b2 boosters administered via intramuscular or intradermal routes in a Thai geriatric population DESIGN: Prospective, randomized, open-labeled.

SETTING

Siriraj Hospital, Thailand.

PARTICIPANTS

Geriatric adults aged ≥65 years.

INTERVENTION

10 μg intradermal or 30 μg intramuscular BNT162b2 (Pfizer-BioNTech).

MEASUREMENTS

Anti-SARS-CoV-2 receptor binding domain IgG, neutralizing antibodies (NAb), and interferon-gamma producing cells against Wuhan and Omicron BA.4/5. Analyses were stratified based on participants' Clinical Frailty Scale.

RESULTS

A total of 139 participants were included in the analysis. Two-four weeks post-booster administration, NAb titers against Wuhan but not Omicron BA.4/5 were significantly lower among frail participants than non-frail participants who received intramuscular administration. Spike-specific T cell responses were similar for frail and non-frail participants, regardless of administration route. Frail participants who received intradermal BNT162b2 had fewer local adverse events (AEs), but higher systemic AEs than non-frail participants.

CONCLUSION

Similar immune responses across vaccine routes warrants further evaluation of intradermal BNT162b2 in frail geriatric populations. Frail participants may be more sensitive to reporting systemic AEs.

REGISTRATION OF CLINICAL TRIALS

The parent study was registered under the Thai Clinical Trials Registry (TCTR20220112002).

Predicting Efficacies of Fractional Doses of Vaccines by Using Neutralizing Antibody Levels: Systematic Review and Meta-Analysis

Background

With the emergence of SARS-CoV-2 variants that have eluded immunity from vaccines and prior infections, vaccine shortages and vaccine effectiveness pose unprecedented challenges for governments in expanding booster vaccination programs. The fractionation of vaccine doses might be an effective strategy for helping society to face these challenges, as fractional doses may have efficacies comparable with those of the standard doses.

Objective

This study aims to investigate the relationship between vaccine immunogenicity and protection and to project efficacies of fractional doses of vaccines for COVID-19 by using neutralizing antibody levels.

Methods

In this study, we analyzed the relationship between in vitro neutralization levels and the observed efficacies against both asymptomatic infection and symptomatic infection, using data from 13 studies of 10 COVID-19 vaccines and from convalescent cohorts. We further projected efficacies for fractional doses, using neutralization as an intermediate variable, based on immunogenicity data from 51 studies included in our systematic review.

Results

In comparisons with the convalescent level, vaccine efficacy against asymptomatic infection and symptomatic infection increased from 8.8% (95% CI 1.4%-16.1%) to 71.8% (95% CI 63%-80.7%) and from 33.6% (95% CI 23.6%-43.6%) to 98.6% (95% CI 97.6%-99.7%), respectively, as the mean neutralization level increased from 0.1 to 10 folds of the convalescent level. Additionally, mRNA vaccines provided the strongest protection, which decreased slowly for fractional dosing with dosages between 50% and 100% of the standard dose. We also observed that although vaccine efficacy increased with the mean neutralization level, the rate of this increase was slower for vaccine efficacy against asymptomatic infection than for vaccine efficacy against symptomatic infection.

Conclusions

Our results are consistent with studies on immune protection from SARS-CoV-2 infection. Based on our study, we expect that fractional-dose vaccination could provide partial immunity against SARS-CoV-2 and its variants. Our findings provide a theoretical basis for the efficacy of fractional-dose vaccines, serving as reference evidence for implementing fractional dosing vaccine policies in areas facing vaccine shortages and thereby mitigating disease burden. Fractional-dose vaccination could be a viable vaccination strategy comparable to full-dose vaccination and deserves further exploration.

Dynamics of Anti-SARS-CoV-2 IgA and IgG Responses and Their Protective Effect against Fatal Disease after Booster COVID-19 Vaccination

During the post-coronavirus disease (COVID-19) era, a primary question is whether booster vaccination is effective against severe COVID-19 and should be recommended, particularly to individuals at high risk for severe disease (i.e., the elderly or those with additional severe comorbidities). From December 2020 to February 2023, a cohort study was conducted to estimate IgG and IgA immunogenicity and the dynamics of booster mono- and bivalent COVID-19 mRNA vaccines in 260 individuals (male/female: 114/146, median age: 68 years, interquartile range (IQR) = 31) who initially received either mRNA (218) or adenovirus-vector-based vaccines (42). Participants were followed until the 90th day after the third booster dose. Our cohort study indicated a beneficial effect of booster vaccination on the magnitude of IgG and IgA severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies. We found that second and third booster doses were more protective than one against fatal disease (p = 0.031, OR 0.08). In conclusion, booster COVID-19 vaccination should be strongly recommended, especially to individuals at high risk for severe/fatal disease.