Nielsen, SebastianFisker, Ane BSie, AliMüller, OlafNebie, EricBecher, Heikovan der Klis, FionaBiering-Sørensen, SofieByberg, StineThysen, Sanne Mda Silva, IsaquelRodrigues, AmabeliaMartins, CesarioWhittle, Hilton CAaby, PeterBenn, Christine S2025-01-032025-01-032024-08-303921814110.1016/j.ijid.2024.107224https://rivm.openrepository.com/handle/10029/628012Between 2003 and 2019, three trials (randomised controlled trials [RCTs]) in Guinea-Bissau randomised infants to an early 2-dose measles vaccine (MV) schedule at 4 and 9 months vs standard MV at 9 months. The RCTs produced contradictory mortality results; the effect being beneficial in the 2-dose group in the first but tending to have higher mortality in the last two RCTs. We hypothesised that increased frequency of campaigns with oral polio vaccine (C-OPV) explained the pattern.We performed per-protocol analysis of individual-level survival data from the three RCTs in Cox proportional hazards models yielding hazard ratios (HR) for the 2-dose vs the 1-dose MV group. We examined whether timing of C-OPVs and early administration of OPV0 (birth to day 14) affected the HRs for 2-dose/1-dose MV.The combined HR(2-dose/1-dose) was 0.79 (95% confidence interval: 0.62-1.00) for children receiving no C-OPV-before-enrolment, but 1.39 (0.97-1.99) for those receiving C-OPV-before-enrolment (homogeneity, P = 0.01). C-OPV-before-enrolment had a beneficial effect in the 1-dose group but tended to have a negative effect in the 2-dose group, especially in females. These effects were amplified further by early administration of OPV0.In the absence of C-OPVs, an early 2-dose MV strategy had beneficial effects on mortality, but frequent C-OPVs may have benefitted the 1-dose group more than the 2-dose MV group, leading to varying results depending on the intensity of C-OPVs.enCopyright © 2024. Published by Elsevier Ltd.CampaignsChild mortalityMeasles vaccineNon-specific effects of vaccinesOral polio vaccineArticleInt J Infect Dis 2024;148:107224S1201-9712(24)00295-9