The association of oral polio vaccine doses and severity of paralysis: an analysis of wild poliovirus type 1 cases in Pakistan

Background Wild poliovirus type 1 (WPV1) transmission persists in Pakistan, with cases increasing from 6 in 2023 to 56 by November 2024, highlighting critical challenges in polio eradication efforts. The aim of this study is to assess the relationship between bivalent oral polio vaccine (bOPV) doses and the severity of paralysis in the confirmed WPV1 cases in Pakistan.Methods We analysed all confirmed WPV1 cases reported in Pakistan from January 1, 2024, to November 15, 2024. Bivariate analyses were first conducted to explore initial associations. Firth, logistic regression models were then employed to evaluate the strength of these associations while adjusting for potential confounders.Results Higher bOPV doses were significantly associated with a lower risk of severe paralysis in both univariate analysis (OR = 0.75, 95% CI: 0.60–0.93, p = 0.009) and after adjustment for age and sex (OR = 0.76, 95% CI: 0.59–0.97, p = 0.026). For residual paralysis after 60 days of onset, univariate analysis showed a significant association (OR = 0.77, 95% CI: 0.61–0.97, p = 0.026); however, this association was no longer statistically significant after adjustment (OR = 0.82, 95% CI: 0.64–1.05, p = 0.115).Conclusion The study found a significant association between higher bOPV dose count and reduced paralysis severity in confirmed WPV1 cases. These findings suggest that bOPV may help to moderate the severity of paralysis, in addition to preventing WPV1 infection.