[Adverse effect incidence of Pfizer/BioNTech COVID-19 vaccine: Retrospective cohort study].

Background: Coronavirus SARS-CoV-2 has been the cause of multiple hospitalizations due to respiratory distress, pneumonia, multi-organic failure and death in all the world. The BioNTech/Pfizer lab was the first to get the approval from the Food and Drug Administration (FDA) for vaccine application, beginning with health workers. However, there are a few studies about adverse effects after applying the COVID-19 vaccine.

Objective: To assess the presence and time of onset of adverse effects produced by the COVID-19 vaccine.

Material and methods: A retrospective cohort study was carried out, including medical residents from the Hospital de Especialidades No. 1 (Specialties Hospital No. 1) from the Bajío National Medical Center, who received two doses of Pfizer-BioNTech vaccine and decided to participate voluntarily. We obtained the information by a self-assessment tool sent via email. All adverse effects were collected emphasizing those described in the literature.

Results: A total of 101 medical residents were included. It was observed that 55.54% presented adverse effects after the first dose, which appeared in the first 24 hours after the vaccine was administered. After the second dose, 54.5% presented symptomatology, 41.6% during first 24 hours after the vaccine was administered.

Conclusions: It was observed symptomatology after applying the complete series (two doses) of BioNTech/Pfizer; however, there were mild and of short duration.