ABSTRACT
Background: Oral polio vaccine (OPV) may improve resistance to non-polio-infections. We tested whether OPV reduced the risk of illness and mortality before coronavirus disease 2019 (COVID-19) vaccines were available. Methods: During the early COVID-19 pandemic, houses in urban Guinea-Bissau were randomized 1:1 to intervention or control. Residents aged 50+ years were invited to participate. Participants received bivalent OPV (single dose) or nothing. Rates of mortality, admissions, and consultation for infections (primary composite outcome) during 6 months of follow-up were compared in Cox proportional hazards models adjusted for age and residential area. Secondary outcomes included mortality, admissions, consultations, and symptoms of infection. Results: We followed 3726 participants (OPV, 1580; control, 2146) and registered 66 deaths, 97 admissions, and 298 consultations for infections. OPV did not reduce the risk of the composite outcome overall (hazard ratio [HR] = 0.97; 95% confidence interval [CI], .79-1.18). OPV reduced the risk in males (HR = 0.71; 95% CI, .51-.98) but not in females (HR = 1.18; 95% CI, .91-1.52) (P for same effect = .02). OPV also reduced the risk in Bacillus Calmette-Guérin scar-positive (HR = 0.70; 95% CI, .49-.99) but not in scar-negative participants (HR = 1.13; 95% CI, .89-1.45) (P = .03). OPV had no overall significant effect on mortality (HR = 0.96; 95% CI, .59-1.55), admissions (HR = 0.76; 95% CI, .49-1.17) or recorded consultations (HR = 0.99; 95% CI, .79-1.25), but the OPV group reported more episodes with symptoms of infection (6050 episodes; HR = 1.10 [95% CI, 1.03-1.17]). Conclusions: In line with previous studies, OPV had beneficial nonspecific effects in males.