Surveillance of COVID-19 vaccines: A comprehensive analysis of the first immunization drive in Ecuador.

The initial phase of the COVID-19 vaccination in Ecuador occurred between April and November 2021. Initially, it focused on priority populations, including health professionals and other front-line workers. During this period, there was limited knowledge about the vaccine's adverse effects. A non-probability, observational study was conducted among university staff in Guayaquil, Ecuador, who received the AstraZeneca vaccine (n = 423) between April and November 2021. This study aimed to compare the acute adverse reactions by doses and to report the incidence of long-term adverse reactions within the AstraZeneca group. As a result, comparing acute adverse reactions between doses, the odds ratio for local pain, headache, muscle pain, fever, and chills are statistically higher after the first dose than the second dose. Survival curves indicated these symptoms appeared mainly within the first 6 h post-vaccination. This is the first pharmacovigilance study from Ecuador that analyzes survival probabilities for the AstraZeneca vaccine's adverse effects.