Comparative Effectiveness of Recommended and Delayed Dosing Schedules for Rotavirus Vaccine: Target Trial Emulation

Background: Live oral rotavirus vaccines were found to be less effective in low-income countries compared to high-income countries when using the same product and dosing schedule. We investigated whether altering dose timing may improve immune protection using a target trial emulation approach. Methods: We emulated a target trial with clone-censor weighting to compare the effectiveness of the recommended 2-dose rotavirus vaccine schedule with a delayed schedule among children under two years of age in Peru and Brazil. Secondary data from the Malnutrition and Enteric Disease Study (MAL-ED) birth cohort (2009-2014) were analyzed. Children were followed from the date of birth until the earliest occurrence of a rotavirus outcome (infection confirmed by PCR or enzyme immunoassay (EIA) or diarrhea confirmed by EIA), protocol nonadherence, loss to follow-up, or their second birthday. Results: We included 154 children in Brazil and 192 in Peru. At two years of follow-up, the risk ratio (RR) for PCR-confirmed infection, using the recommended schedule as the reference, was 1.00 (95% confidence interval [CI]: 0.73-1.37) in Peru and 0.85 (95% CI: 0.31-1.66) in Brazil. In Peru, the delayed schedule was associated with a higher cumulative risk of EIA-confirmed rotavirus diarrhea (RR at two years: 1.73; 95% CI: 1.02-2.77). Conclusions: Delaying the two-dose rotavirus vaccine schedule did not change the cumulative risk of rotavirus infection, but the delayed schedule was associated with a higher risk of rotavirus diarrhea in Peru, where rotavirus incidence was higher.