Comparison of physiological and clinical reactions to COVID-19 and influenza vaccination

Public reluctance to receive COVID-19 vaccination is associated with safety concerns. By contrast, the seasonal influenza vaccine has been administered for decades with a solid safety record and a high level of public acceptance. We compare the safety profile of the BNT162b2 COVID-19 booster vaccine to that of the seasonal influenza vaccine. We study a prospective cohort of 5079 participants in Israel and a retrospective cohort of 250,000 members of MHS selected randomly. We examine reactions to BNT162b2 mRNA COVID-19 booster and to influenza vaccinations. All prospective cohort participants wore a smartwatch and completed a daily digital questionnaire. We compare pre-vaccination and post-vaccination smartwatch heart-rate data, and a stress measure based on heart-rate variability. We also examine adverse events from electronic health records. In the prospective cohort, 1905 participants receive the COVID-19 booster vaccine; 899 receive influenza vaccination. Focusing on those who receive both vaccines yields a total of 689 participants in the prospective cohort and 31,297 members in the retrospective cohort. Individuals reporting a more severe reaction after influenza vaccination tend to likewise report a more severe reaction after COVID-19 vaccination. In paired analysis, the increase in both heart rate and stress measure for each participant is higher for COVID-19 than for influenza in the first 2 days after vaccination. No elevated risk of hospitalization due to adverse events is found following either vaccine. Except for Bell's palsy after influenza vaccination, no elevated risk of adverse events is found. The more pronounced side effects after COVID-19 vaccination may explain the greater concern associated with it. Nevertheless, our comprehensive analysis supports the safety profile of both vaccines. We compared the safety profiles of the COVID-19 and influenza vaccines. We analyzed data from Israel involving 5079 participants who wore smartwatches and completed daily questionnaires, as well as electronic health records from 250,000 members of Maccabi Healthcare Services. We found that side effects after the COVID-19 vaccine were more noticeable, based on self-reported symptoms and heart measures (heart-rate and stress) detected by smartwatches. The increase in heart measures was higher after COVID-19 vaccination than after influenza vaccination in the first 2 days post-vaccination. However, electronic health records showed no increased risk of adverse events with the COVID-19 and influenza vaccines. Our analysis supports the safety of both vaccines but may explain the greater concern about the COVID-19 vaccine. Yechezkel et al. compare the safety profiles of the BNT162b2 COVID-19 booster and the seasonal influenza vaccine using data from wearables, reported reactions, and electronic health records. Participants displayed increased heart rates and short-term stress measurements following COVID-19 boosters but overall safety of both vaccines is supported.