IPV introduction in the routine vaccination programme in 2016 and subsequent shortage: a natural experiment in Guinea-Bissau

Background As part of the global polio eradication strategy, oral polio vaccine (OPV) will be replaced by the inactivated polio vaccine (IPV). Despite protection against polio, studies suggest that IPV may negatively affect child health, particularly for females. Methods In 2016, IPV was introduced to be co-administered with the third OPV (OPV3), and third pentavalent (diphtheria-tetanus-pertussis-haemophilus influenzae type B-hepatitis B) vaccine (penta3) at age 3.5 months. In a natural experiment arising from IPV introduction, shortage, and subsequent re-introduction, we compare the risk of outpatient non-accidental consultation, hospital admission and mortality after vaccination with penta3 + OPV3 + IPV versus penta3 + OPV3 in urban Guinea-Bissau. Children aged 3–8 months were followed from vaccination to first event. Adjusted hazard ratios (aHR) were estimated with 95% confidence intervals (CI) in Cox-proportional hazards models, overall and by sex. Results Among 5917 children vaccinated from August 2015–July 2019 (penta3 + OPV3 + IPV: 2083; penta3 + OPV3: 3834), we observed 2789 first consultations during 1371 person-years (PYRS), 92 hospital admissions during 1960 PYRS and 17 deaths during 1976 PYRS. Penta3 + OPV3 + IPV was not associated with increased risk of consultation overall (aHR 0.97, 95%CI 0.89–1.06) or among females (aHR 0.89, 95%CI 0.79–1.00). Nor did the risk of admission increase overall (aHR 0.88, 95%CI 0.56–1.37) or among females (aHR 0.69, 95%CI 0.35–1.35). Overall mortality tended to be lower among children receiving IPV (aHR 0.47, 95%CI 0.15–1.48). Yet, regardless of IPV, female mortality was higher than male mortality, the sex-difference being accentuated after IPV introduction ( p = 0.003). Conclusions The risks of consultation, hospital admission and mortality were not increased after penta3 + OPV3 + IPV.