Abstract
OBJECTIVE: To explore the association between human papillomavirus (HPV) vaccination and risk of coronavirus disease 2019 (COVID-19). Specifically, our study aimed to test the hypothesis that HPV vaccination may also induce trained immunity, which would potentially reduce the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and improve clinical outcomes. BACKGROUND: Several vaccines have been reported to trigger non-specific immune reactions that could offer protection from heterologous infections. A recent case report showed that verruca vulgaris regressed after COVID-19, suggesting a possible negative association between COVID-19 and HPV infection. METHODS: We enrolled 57,584 women with HPV vaccination and compared them with propensity score-matched controls who never received HPV vaccination in relation to the risk of COVID-19 incidence. Cox proportional hazard regression analysis was conducted to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Subgroup analyses stratified by age, race, comorbid asthma, and obesity were performed. RESULTS: The risk of COVID-19 incidence was significantly lower in those who had recently received the HPV vaccine (within 1 year after HPV vaccination, aHR: 0.818, 95% CI 0.764-0.876; within 1-2 years after HPV vaccination, aHR: 0.890, 95% CI 0.824-0.961). Several limitations were recognized in this study, including residual confounding, problems of misclassification due to the use of electronic health record data, and that we were unable to keep track of the patients' HPV infection status and the HPV antibody levels in those who had received the vaccine. CONCLUSIONS: Recent HPV vaccination was associated with a lower risk of incident COVID-19 and hospitalization. Based on the promising protective effect of HPV vaccine shown in this study, these findings should be replicated in an independent dataset. Further studies are needed to provide a better understanding of the underlying mechanisms and the differences in risks among 2-, 4-, or 9-valent HPV vaccine recipients.