Single BioNTech/Pfizer vaccine dose reduces risk of COVID-19 by nearly 52%, matching clinical trial data

By James DuckerJun 7 2021

Results from large-scale vaccinations match findings from clinical trials for the BioNTech/Pfizer messenger ribonucleic acid (mRNA) vaccine.

Data gathered from real-world vaccination programs following a single dose of Pfizer vaccine administration shows a reduction of 51.4% in infection risk and effectiveness of 54.4% against symptomatic coronavirus disease 2019 (COVID-19), matching clinical trial results.

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Vaccine effectiveness is consistent between clinical and real-world settings

The widescale implementation of vaccination programs to combat the COVID-19 pandemic has now provided extensive datasets to study vaccine effectiveness in real-world settings and compare this against the results of clinical trials.

This was investigated by a team of researchers in Israel from the Maccabi Institute for Research & Innovation as well as the Department of Epidemiology and Preventive Medicine of Tel Aviv University.

In a new study, the scientists considered the recently authorized BioNTech/Pfizer COVID-19 vaccine (also known as the BNT162b2 vaccine). This vaccine was chosen due to its common administration in Israel and because the vaccine has shown 95% efficacy in preventing COVID-19 with the 2-dose regimen in a phase III placebo-controlled randomized clinical trial, with the second dose given 21 days after the first vaccine dose.

The researchers tested whether the cumulative incidence of SARS-CoV-2 infection among individuals who received the BNT162b2 vaccine would decline after 12 days after immunization compared with the incidence during the preceding 12 days, and if this was consistent with clinical trial data.

Data was gathered from 503 875 individuals who received 1 dose of the Pfizer vaccine, with over half providing follow-up data for the following 3 weeks on the incidence of SARS-CoV-2 infection. Participants included individuals aged 16 years and older who received a single dose of the Pfizer vaccine between December 19, 2020, and January 15, 2021. The average age of patients was 59 years old, with nearly 53% of patients being women.

Altogether, findings revealed the single dose of vaccine was associated with 54% effectiveness against symptomatic COVID-19.

Findings also showed that the first dose of the vaccine was associated with an approximately 51% reduction in the risk of SARS-CoV-2 infections at 13 to 24 days after immunization compared with 1 to 12 days after vaccination. This indicates that the temporal aspect of vaccine administration is consistent with clinical trials occurring at the 3-week mark.

Real-world vaccination effectiveness maintained across demographic factors

The extensive dataset also provided researchers with further insight into potentially confounding factors such as age, gender, regional differences, and patients with previous medical conditions. Such factors would reveal whether portions of the population were particularly at risk, including high-risk patients such as older patients with medical histories.

The researchers, therefore, considered these factors in further analyses, demonstrating that vaccine effectiveness was maintained among individuals aged 60 years or older (44.5%), those younger than 60 years (50.2%), women (50.0%) and men (52.1%).

Findings were also similar across subpopulations (e.g. ultraorthodox Jewish: 53.5%) and patients with various comorbidities (e.g. cardiovascular diseases; 47.2%).

Considering potential confounding variables is indicative of the strengths of the analysis in the present study. The study also provides several additional strengths, including the use of large-scale automated data collection of vaccination status and laboratory results across all citizens free of charge. This provides a unique opportunity to explore vaccine effectiveness with minimal threat of the information bias that characterizes studies relying on a self-reported diagnosis.

Examining temporal changes in effectiveness and addressing limitations

A particularly advantageous perspective offered by the current analysis is the consideration of changes in vaccine effectiveness over time. This factor may be particularly insightful when comparing results to other vaccination types as well as the effectiveness of disease prevention programs across countries. Establishing the demographic groups at the highest risk for priority vaccination is a key aspect, yet few programs consider how temporal dimensions can alter herd immunity dynamics.

The present analysis was hindered by two key limitations that could be further examined in future research. First, despite the relatively large study population, the analysis was limited by the number of individuals with chronic illness who became infected with SARS-CoV-2 during the short study period. Second, are the decreased test rate 2 weeks after the first dose, which may have caused more asymptomatic infections to go undocumented and which may confound the analysis slightly.

Nevertheless, these challenges can be overcome using more refined data from hospital environments as well as in more recent data, as a larger proportion of the population has now been vaccinated with both doses.