Adverse effects to the Pfizer-BioNTech vaccine in staff of a tertiary hospital

Introduction: One of the vaccines to combat the COVID-19 coronavirus pandemic was the RNA-messenger vaccine developed by Pfizer-BioNTech. In early 2021, hospital workers in Mexico received two doses of this vaccine. The objective of this study was to determine the frequency of adverse events (AE) to the Pfizer-BioNTech vaccine in a cohort of staff at a tertiary hospital in southeastern Mexico and to identify factors associated with the development of AE. Method: Cross-sectional, observational and descriptive study carried out in the staff of a tertiary hospital. AE's were identified through active surveillance and telephone follow-up between the second and fifteenth day afterthe first and second immunization. Demographic and clinical data were captured in an electronic database. Results: A total of 1033 subjects were surveyed, with a mean age of 39.04 +/- 9.20 years and 53.4% female. 94.5% of subjects experienced at least one AE after administration of the Pfizer-BioNTech vaccine. A total of 2805 AEs were detected (1360 first dose and 1445 second dose). The most frequently reported AEs at both doses were application site pain, headache, fatigue and pyrexia. Conclusions: The frequency of AEs in the present study was consistent with previous reports for the Pfizer-BioNTech vaccine. AEs were mild and transient showing good tolerability. Female sex, having a chronic-degenerative disease and a history of allergy were significantly associated with the presence of any AE.