A team of scientists in Israel recently evaluated the efficacy of an mRNA-based coronavirus disease 2019 (COVID-19) vaccine, BNT162b2 (also known as the Pfizer-BioNTech vaccine), in inducing host humoral immune response.
The findings reveal that the vaccine is capable of inducing strong anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody response and that the response varies significantly with age. The study is currently available on the medRxiv* preprint server.
As of March 7, 2021, there have been 116 million confirmed COVID-19 cases, including 2.5 million deaths, reported to the World Health Organization (WHO). Besides discovering and repurposing potent anti-viral therapeutic approaches, several potential vaccines have been produced in record speed as an attempt to prevent further transmission of SARS-CoV-2. Many of these vaccines have already received emergency use approval from national regulatory authorities across the globe. As of March 8, 2021, around 249 million vaccine doses have been administered globally, according to the WHO data.
In Israel, the large-scale administration of the COVID-19 vaccine BNT162b2 has been started in mid-December 2020 after obtaining a highly affirmative response from a randomized placebo-controlled vaccine trial. Recently, studies conducted in nation-wide mass vaccination settings have reported that the BNT162b2 vaccine is highly effective in preventing symptomatic COVID-19, hospitalization rate, severe complications, and death.
In the current study, the scientists have evaluated the anti-SARS-CoV-2 antibody responses among Israeli healthcare workers vaccinated with BNT162b2. Specifically, BNT162b2 is a lipid-nanoparticle formulated, mRNA-based vaccine that contains perfusion-stabilized, membrane-bound full-length SARS-CoV-2 spike protein as a vaccine antigen.
The study was conducted on a total of 116 healthcare staff working in one of the largest healthcare organizations in Israel. Of all participants, 48 were below 50 years of age and 68 were above 50 years of age. About 8% of the participants were male.
All participants were administered with 2 doses of the vaccine at an interval of 21 days. The serological tests for SARS-CoV-2 spike protein-specific IgG antibodies were conducted serially between January 14, 2020, and February 24, 2021. On average, 3 serological tests were conducted for each participant, leading to a total of 382 tests.
As evident from the findings, seroconversion occurred in all participants 14 days after immunization with the first dose. The titers of SARS-CoV-2 spike protein-specific IgG antibodies reached a peak value by around day 30, which was 10 days after the second dose.
The scientists observed a variation in antibody response among participants aged below or above 50 years. The participants who were below 50 years of age showed higher antibody levels in the blood. Importantly, the scientists observed that despite gender-wise variations, the antibody levels remained significantly higher than the threshold for serological reactivity.
Regarding the durability of the vaccine’s effect, the scientists observed that after peaking, the antibody response decayed very slowly throughout the study period (six weeks).
Overall, the study findings indicate that the mRNA-based COVID-19 vaccine BNT162b2 is highly effective in inducing robust antibody response against SARS-CoV-2. Although the vaccine showed higher efficacy among younger participants, the scientists believe that further studies are needed to accurately evaluate the long-term dynamics of such age-related variations. They have also highlighted the need for exploring other factors that may influence the rate of seroconversion.
Since the study duration was restricted to only six weeks, the long-term efficacy of the vaccine could not be explored. Moreover, because of the relatively small sample size and disproportionate male to female ratio, the study cohort is not a true representative of the general population. These might be the potential limitations of the study, as mentioned by the scientists.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information