Background and importance Since December 2019, the world has faced a new disease known as COVID-19. On 11 March 2020, the World Health Organization officially declared the COVID-19 pandemic. Given the health emergency, vaccine development progressed rapidly, but with limited safety data under real-world conditions.

Aim and objectives To describe and compare the incidence of adverse events with the BNT162b2 and mRNA-1273 COVID-19 vaccines, taking into account the number of doses and subjects previously positive for SARS-CoV-2 infection.

Material and methods A retrospective observational study was conducted in a tertiary hospital between March and April 2021. Data were collected through a questionnaire sent by email to hospital staff. Demographics and data regarding the occurrence of adverse events were collected, indicating which vaccine was administered. Statistical analysis was performed using SPSS software. Groups were compared using the Chi-square test and Fisher’s exact test when necessary.

Results 1249 respondents completed the survey (25% of all hospital staff); 52% (650) received BNT162b2 vaccine and 48% (599) mRNA-1273. 14 402 adverse reactions were recorded. 6896 were local: 3939 were with mRNA-1273 and 2957 with BNT162b2 (6.6 vs 4.4 reactions per patient); and 7506 were systemic: 4460 with mRNA-1273 and 3046 with BNT162b2 (7.4 vs 4.7 per patient). The occurrence of local reactions was 95.8% after the first dose/89.1% after the second dose with mRNA-1273 versus 89.7%/82.5% with BNT162b2. For systemic reactions, this proportion was 64.3%/93.3% versu 46.8%/73.2% (p value<0.05).

In terms of severity, 379 patients (63.3%) with mRNA-1273 confirmed a severe reaction versus 222 (34.2%) with BNT162b2 and 60 patients (10%) with mRNA-1273 confirmed an urgent reaction versus 33 (5.1%) with BNT162b2 (p value<0.001). For both vaccines, there was no difference in the occurrence of local or systemic reactions between patients seropositive and seronegative for SARS-CoV-2.

Conclusion and relevance The results are consistent with the limited data available to date, confirming that although these are not particularly serious adverse effects, they do occur in a large majority of vaccinated persons and in greater numbers after administration of the mRNA-1273 vaccine. The Hospital Pharmacy Service is a key agent in pharmacovigilance within the healthcare system and must be aware of the safety profile of new drugs. This study is an essential tool to detect and prevent adverse events.

Conflict of interest No conflict of interest