Abstract
BACKGROUND: The World Health Organization declared COVID-19 a pandemic in March 2020. The first vaccine became available in December, with practically no post-marketing data. METHODS: An analytical cross-sectional survey-based study was conducted in a third-level hospital in Spain between March and April 2021 to describe the difference in adverse events with the BNT162b2 and mRNA-1273 COVID-19 vaccines. The participants were hospital workers who completed a survey voluntarily at least 14 days after the last vaccine. The STROBE checklist was followed. RESULTS: One thousand two hundred and forty-nine respondents completed the survey; 48% (599) received mRNA-1273 and 52% (650) BNT162b2. Fourteen thousand four hundred and two adverse reactions were recorded, 6896 local (3939 with mRNA-1273 and 2957 with BNT162b2 (6.6 vs 4.4 reactions per patient)) and 7506 systemic (4460 with mRNA-1273 and 3046 with BNT162b2 (7.4 vs 4.7 per patient)). Local reactions were more frequent after the first dose, while systemic reactions were higher after the second, for both vaccines and in a higher percentage with mRNA-1273 compared to BNT162b2 (p-value<0.05). CONCLUSIONS: Licensed mRNA vaccines were highly safe when administered under post-marketing conditions among working-age adults. The main adverse events were mild, although they occurred in most patients, especially after the mRNA-1273 vaccine.