RESUMEN
OBJECTIVES: To describe the incidence of adverse events (AEs), reactogenicity symptoms, menstrual changes and overall self-rated improvement in health and well-being after COVID-19 vaccination. DESIGN: VAC4COVID is an ongoing prospective, active observational, post-authorisation cohort safety study (PASS) of UK-approved vaccines for COVID-19 disease. SETTING: The study is conducted through a secure website (www.vac4covid.com) by MEMO Research, University of Dundee, UK. PARTICIPANTS: 16 265 adult (18 years or older) UK residents with a valid email address and internet access. INTERVENTIONS: Any UK-authorised COVID-19 vaccination. MAIN OUTCOME MEASURES: The outcomes reported in this interim analysis include AEs, reactogenicity-type AEs (headache, fatigue, muscle or joint pain, fever, nausea, dizziness or local vaccine reaction), menstrual changes and reported improvement in overall health and well-being. RESULTS: 11 475 consented participants (mean age 54.8 years) provided follow-up data between 2 February and 5 October 2021 (mean follow-up duration 184 days), by which date 89.2% of participants had received two vaccine doses. 89.8% of 5222 participants who completed a follow-up questionnaire in the 7 days after any COVID-19 vaccination reported no AEs. The risk of experiencing any event (not necessarily vaccine-related) requiring hospitalisation was less than 0.2%. 43.7% of post-vaccination follow-up records reported improvement in health and well-being. Reactogenicity-type reactions were more common in the week after the first dose of ChAdOx1 than BNT162b2 (7.8% vs 1.6%), but this relationship was reversed after the second dose (1.3% vs 3.1%). 0.3% of women reported menstrual symptoms after vaccination; no differences between vaccine type or dose order were detected. CONCLUSIONS: The study provides reassuring data on low rates of AEs after COVID-19 vaccination. Differences in reactogenicity-type AE profiles between ChAdOx1 and BNT162b2 and between first and second doses of these vaccines were observed. TRIAL REGISTRATION NUMBER: ISRCTN95881792; Pre-results.