Booster vaccines are a strategy to mitigate the conditions in the health, social, and economic fields that the COVID-19 pandemic has brought. A series of adverse effects have been observed since the first vaccination. The present investigation aims to describe the short-term adverse effects of the fourth dose against COVID-19 in adults older than 40 from a region of Peru. The study population was over 40 years of age at the COVID-19 vaccination center in Trujillo, Peru. A 21-day follow-up was conducted from vaccination with the fourth dose, considering sex, age, body mass index, comorbidities, history of COVID-19 infection, vaccination schedule, and simultaneous vaccination against influenza as variables of interest. Multinomial logistic regression with robust variance was used to estimate the risk ratio (RR). In total, 411 people were recruited, and it was found that 86.9% of the participants presented adverse effects after injection with the fourth dose of the vaccine against COVID-19. Pain at the injection site was the most reported symptom after 3 days. Assessment of adverse effects after 3 days found that age ≥ 60 years was associated with a lower likelihood of adverse effects compared to those younger than 60 years (RRc: 0.32; 95% CI: 0.0.18-0.59), males compared to females were associated with a lower likelihood of adverse effects (RRc: 0.54; 95% CI 0.30-0.98), being overweight (RRc: 2.34; 95% CI: 1.12-4.89), and last vaccine with Pfizer-BioN-Tech (RRc: 0.42; 95% CI: 0.18-0.96). Associated adverse effects are mild to moderate. Injection site pain and general malaise are the most frequent adverse effects.
Keywords: COVID-19; Peru; adverse effects; vaccines.