Background and importance Although clinical trials of the BNT162b2 mRNA vaccine against COVID-19 (Pfizer-BioNTech) have shown acceptable levels of safety, continuous monitoring of the reactogenicity of the vaccine outside of controlled settings in clinical trials can provide additional information for patients, health professionals and the general population on local and systemic reactions after vaccination.

Aim and objectives To analyse the reactogenicity of the first and second doses of the mRNA vaccine against COVID-19 BNT162b2 (Pfizer-BioNTech) in a sample of tertiary hospital workers.

Material and methods 295 tertiary hospital workers who received the BNT162b2 vaccine against COVID-19 between January and March 2021 answered a questionnaire on sociodemographic variables, previous COVID-19 infection, and local and systemic reactions after the first and second doses of the vaccine.

Results 291 completed the questionnaire after the first and second doses of the vaccine (response rate of 95.4%), which constituted the final sample of the study. Of these, 200 were women (68.7%), and the mean age was 48.46 (SD 11.77) years. 81.8% and 84.0% of the participants indicated having experienced at least one adverse reaction after the first and second doses of the vaccine, respectively. The most commonly reported reaction was pain at the injection site, being more frequent after the first dose of the vaccine. Systemic reactions evaluated were reported more frequently after the second dose of the vaccine. The most frequent reactions to the first dose were pain at the injection site (74.6%), headache (11.3%) and fatigue (9.3%). In the second dose, the most frequent reactions were pain at the injection site (64.8%), general malaise (30.7%) and headache (26.8%). Women, younger adults and people with a previous COVID-19 infection reported increased reactogenicity. Furthermore, a high reactogenicity after the first dose was related to a higher number of adverse reactions after the second dose of the vaccine.

Conclusion and relevance The distribution of reactogenicity in the present study is consistent with the data reported in the studies conducted with the BNT162b2 vaccine, especially in terms of association with the characteristics of the participants. These findings can facilitate the identification of people with a higher probability of having a high reactogenicity to the vaccine, allowing them to anticipate its appearance.

Conflict of interest No conflict of interest