From the Guidelines
The absolute risk reduction (ARR) of the Pfizer COVID-19 vaccine is approximately 0.84%, as reported in the initial clinical trials 1. This means that for every 119 people who received the vaccine instead of placebo, one additional COVID-19 case was prevented. While this number appears small compared to the widely reported relative risk reduction of 95%, it's essential to understand that absolute risk reduction reflects the actual difference in infection rates between vaccinated and unvaccinated groups during the limited trial period. The ARR is influenced by the overall infection rate during the study period, which was relatively low. Despite the seemingly modest absolute risk reduction, the vaccine has proven highly effective at preventing severe disease, hospitalization, and death from COVID-19 across various populations, as supported by recent guidelines from the Advisory Committee on Immunization Practices 1. When evaluating vaccine efficacy, both relative and absolute risk reductions provide valuable but different perspectives on the vaccine's impact, with ARR giving a more concrete measure of the actual number of infections prevented in a specific timeframe. It's also worth noting that the vaccine's effectiveness has been demonstrated in various age groups, including those aged 5–11 years, for whom the bivalent Pfizer-BioNTech COVID-19 vaccine is recommended 1. Additionally, the vaccine has been shown to be effective in preventing COVID-19 in individuals with underlying conditions, such as diabetes, as highlighted in the standards of medical care in diabetes-2022 1. Overall, the Pfizer COVID-19 vaccine has been proven to be a crucial tool in preventing COVID-19 and its severe outcomes, and its use is recommended by the Advisory Committee on Immunization Practices for persons aged ≥5 years 1.
From the Research
Absolute Risk Reduction of the Pfizer (Comirnaty) COVID-19 Vaccine
- The absolute risk reduction of the Pfizer (Comirnaty) COVID-19 vaccine is 0.7% (95% CI, 0.59% to 0.83%; p < 0.000) as reported in a critical appraisal of the vaccine's efficacy 2.
- This measure indicates the difference in the risk of developing COVID-19 between the vaccinated and unvaccinated groups.
- The absolute risk reduction is a more nuanced measure of vaccine efficacy than relative risk reduction, as it takes into account the baseline risk of the disease in the population.
- In contrast to the high relative risk reduction of 95.1% (95% CI, 90.0% to 97.6%; p = 0.016), the absolute risk reduction of 0.7% provides a more accurate representation of the vaccine's effectiveness in preventing COVID-19 2.
Comparison with Other Studies
- Other studies have reported varying estimates of the absolute risk reduction for COVID-19 vaccines, ranging from 6 to 17 per 1000 across different trials 3.
- A narrative review of 19 COVID-19 vaccines found that all vaccines had high efficacy against the original strain and variants of concern, but the quality of evidence varied depending on the vaccine 4.
- A study evaluating the effectiveness of COVID-19 vaccines in preventing hospitalization among adults aged ≥65 years found that the Pfizer-BioNTech vaccine had an effectiveness of 96% (95% CI = 94%-98%) in preventing COVID-19-associated hospitalization among adults aged 65-74 years 5.