Evidence of Rebound Malaria: Estimating the Impact of Malaria Transmission Intensity on Reduced Malaria Vaccine Efficacy in Sub-Saharan Africa

Keywords: malaria, vaccine, health, medical, public health, ecological, africa, sub-saharan
Session Type: Virtual Paper Abstract
Day: Monday
Session Start / End Time: 2/28/2022 09:40 AM (Eastern Time (US & Canada)) - 2/28/2022 11:00 AM (Eastern Time (US & Canada))
Room: Virtual 46

Abstract

RTS,S/AS01 is the world’s first malaria vaccine to be licensed and undergo pilot implementation. The efficacy of the vaccine in young children is variable, ranging from 22% in Mozambique to 75% in Kenya. Initial evidence suggests that vaccine efficacy is lower in sites with high-malaria incidence. Potential mechanisms include a “rebound” effect where vaccinated children may have higher cases of malaria compared to unvaccinated children over time. Using data from a 5-year trial in Malawi, Ghana and Gabon, we evaluate the rebound malaria hypothesis and determine whether malaria incidence is modified by malaria exposure (transmission intensity). We estimated malaria exposure for each geocoded participant using remotely-sensed and survey-collected ecological variables from the natural, social and built environment using a random forest model. We then evaluated whether the relationship between vaccination and malaria incidence is modified by transmission intensity over time. Results show that while vaccinated children had lower malaria incidence within 1 year post-vaccination, malaria transmission intensity had a significant effect on vaccine efficacy over time. In high transmission areas, estimated malaria incidence in vaccinated children increased from 1.95 to 3.66 cases per person-year (CPPY) at 4 years post-vaccination. Conversely, malaria incidence in unvaccinated children reduced from 3.30 to 2.78 CPPY during the same time period. In low-transmission settings, however, the rebound effect was not observed. Results suggest that rebound malaria may contribute to reduced vaccine efficacy in high-transmission areas and future RTS,S vaccination campaigns in those areas should be paired with other interventions to reduce the rebound effect.