Association between COVID-19 Vaccination and Long COVID Symptoms among Adult Residents of Belém, Brazilian Amazon: A Cross-Sectional Study

Objectives To evaluate the long-term sequelae of COVID-19 among adult residents of the Brazilian Amazon, comparing outcomes between vaccinated and unvaccinated individuals, as well as between hospitalized and non-hospitalized patients. The study also examined the association between symptom severity and time elapsed since infection, and assessed the impact of vaccine types and the number of doses received. Methods This cross-sectional observational study included 310 patients diagnosed with long COVID, conducted between 2023 and 2024. Participants were stratified by vaccination status, hospitalization history, duration since acute infection, and symptom severity. Demographic and clinical data were collected via structured interviews and electronic medical record reviews. Statistical analyses utilized Jamovi software with appropriate inferential tests and multivariate logistic regression models. Results Fatigue ( p < 0.001 ), headache ( p = 0.001 ), and muscle weakness ( p = 0.003 ) were the most frequently reported symptoms, predominantly among hospitalized individuals and those with higher symptom burdens. Vaccination was significantly associated with lower symptom prevalence, with the strongest effect observed in recipients of the CoronaVac vaccine. A dose–response relationship was identified, with increasing vaccine doses correlating with decreased symptom frequency. Conclusion Long COVID is a complex condition marked by persistent symptoms, especially in patients with severe initial disease. Vaccination, mainly with multiple doses, was linked to a reduced symptom burden. However, fatigue and headache remained common, underscoring the need for ongoing research into the pathophysiology and targeted therapeutic approaches, particularly considering the unique context of the Amazon region.