Seasonal determinants of access to care: implications for measles outbreak risk in Madagascar

Abstract

BackgroundMeasles containing vaccine was introduced to Madagascar in 1985. Since 2007, intensification of efforts has bought Madagascar closer to the goal of elimination. Nevertheless, recent data also indicate that population immunity might be eroding in the face of high birth rates and barriers to vaccine delivery. Despite evidence that many factors likely to shape vaccination programme effectiveness are seasonal (including transmission, which responds to seasonal human behaviour, and birth rates), how seasonal fluctuations in vaccination shape outbreak risk and timeliness of vaccination is rarely considered. We aimed to evaluate this here. MethodsWe obtained data from the national passive surveillance system for fever and rash in Madagascar from 2004 to 2015 and combined them cross-sectional data for children's vaccination status from the 2008 Demographic Health Survey to characterise seasonality in childhood-infection transmission, access to vaccination, and births, and the signature of extreme climatic events (eg, cyclones). Measles incidence is too low for direct inference into seasonality in transmission, but we leveraged data for rubella, which is likely to have similar drivers. We integrated these data with mathematical models to assess the effect of seasonality in vaccination on outbreak risk and but also timeliness of vaccination—eg, the degree to which children obtain vaccination at the appropriate age. We additionally assessed barriers to vaccination that shape seasonal uptake by pairing this analysis with a detailed case study on vaccination access in a focal region of Madagascar. FindingsSeasonal fluctuations in vaccination coverage can affect measles outbreak risk and interact with seasonality in births to affect the timeliness. While the theoretical optimal seasonal timing of vaccination can be identified, understanding barriers to access to health centers, their staffing, and vaccine supply is essential to strengthening health system functioning, and developing robust responses to extreme climatic events. InterpretationSmall changes in the timing of vaccination are relatively straightforward to implement and have the potential to strengthen vaccination programmes. FundingWellcome Trust.