Self-reported and physiological reactions to the third BNT162b2 mRNA COVID-19 (booster) vaccine dose

Abstract

Background: The rapid rise in hospitalizations associated with the Delta-driven COVID-19 resurgence, and the imminent risk of hospital overcrowding, led the Israeli government to initialize a national third (booster) COVID-19 vaccination campaign in early August 2021, offering the BNT162b2 mRNA vaccine to individuals who received their second dose over five months ago. However, the safety of the third (booster) dose has not been fully established yet. Objective: Evaluate the short-term, self-reported and physiological reactions to the third BNT162b2 mRNA COVID-19 (booster) vaccine dose. Design: A prospective observational study, in which participants are equipped with a smartwatch and fill in a daily questionnaire via a dedicated mobile application for a period of 21 days, starting seven days before the vaccination. Setting: An Israel-wide third (booster) vaccination campaign. Participants: A group of 1503 (18+ years of age) recipients of at least one dose of the BNT162b2 vaccine between December 20, 2020, and September 6, 2021, out of a larger cohort of 2,848 prospective study participants. 1,231 of the participants were recipients of the third vaccine dose. Measurements: Daily self-reported questionnaires regarding local and systemic reactions, mood level, stress level, sport duration, and sleep quality. Heart rate and heart rate variability were continuously measured by Garmin Vivosmart 4 smartwatches. Results: Local and systemic reactions reported following the third (booster) dose administration are similar to those reported following the second dose and considerably greater than those reported following the first dose. Our analyses of self-reported well-being indicators as well as the objective heart rate and heart rate variability measures recorded by the smartwatches further support this finding. These measures returned to their baseline levels within three days from inoculation with the third dose. These trends were consistent regardless of age, gender or the existence of an underlying medical condition. Limitations: Participants may not adequately represent the vaccinated population in Israel and elsewhere. Conclusion: Our work further supports the safety of a third COVID-19 BNT162b2 mRNA (booster) vaccine dose from both a subjective and an objective perspective. Primary funding source: European Research Council (ERC) project #949850.