Objective:

To determine the incidence of adverse reactions (AR) after the first dose of Pfizer-BioNTech vaccine, and to identify some factors associated with AR.

Method:

A retrospective cohort study was conducted. Data were obtained through an epidemiological survey answered online. Multivariate analyses were performed to identify factors associated with early (< 2 h) and late (≥ 2 h) AR.

Results:

A total of 2295 health care workers were included; in them, the cumulative incidence of AR was 18.2% (95% confidence interval: 16.6-19.8), where the majority were late (78.2%). The associated factors that increased the risk of early AR were being female (odds ratio [OR]: 2.23, p = 0.002) and belonging to the medical staff (OR: 1.56; p = 0.041). In late AR were being female (OR: 1.94; p < 0.0001); on the other hand, diabetes (OR: 0.46; p = 0.021), asthma (OR: 0.53; p = 0.040) and smoking (OR: 0.44, p = 0.002) were inversely associated factors. Interestingly, history of COVID-19 was not associated with either early or late AR.

Conclusions:

The risk of presenting some type of AR due to the Pfizer-BioNTech vaccine in health care workers is < 20%.