Modeling the Vaccination Rate Required to Curb the Madagascar Measles Epidemic

Abstract

Background: Measles has resurged globally. Compounded by widespread malnutrition and high levels of poverty, the country of Madagascar has experienced the largest number of cases worldwide of any country in 2019. According to the World Health Organization, the island nation has reported 81,836 cases between December 2018 and May 2019. Methods: Using HealthMap and Google Search Trends (i.e. nontraditional surveillance data) and World Health Organization (WHO) surveillance data (i.e. traditional surveillance data), the Incidence Decay and Exponential Adjustment (IDEA) model was employed to provide parameter estimates of transmission dynamics, along with the percentage of the susceptible population that needs to be adequately vaccinated to prevent sustained transmission. Results across data sources were compared. Findings: A threshold vaccination rate of 82.6% to 97.9% among the susceptible population is needed to prevent sustained transmission, assuming a two-dose vaccine regimen is used. However, only 80.4% to 95.8% of the susceptible population experiencing sustained transmission is currently vaccinated. A one-dose vaccine regimen resulted in very high or unattainable threshold rates, suggesting the importance of using the two-dose regimen. Parameter estimates from the IDEA model were comparable between nontraditional and traditional surveillance data. Interpretation: Given the lag time associated with availability of and access to traditional surveillance data in low-resource settings like Madagascar, these results suggest that nontraditional surveillance data may be used to assess transmission dynamics of epidemics in near-real-time. By conducting such analyses sooner, relief efforts can be readily initiated in order to more swiftly respond to outbreaks. Funding Statement: N/A. Declaration of Interests: The authors have no conflicts of interest to report. Ethics Approval Statement: Not required.