In collaboration with Dan Neafsey at the Broad Institute, Dyann Wirth at Harvard, Peter Gilbert and Michal Juraska at the Fred Hutch and a large team of researchers, we’ve just published a paper in the New England Journal of Medicine showing strain-specific vaccine efficacy in a recent malaria vaccine trial. We found that the RTS,S malaria vaccine worked better against strains that were genetically matched to the vaccine antigen compared to unmatched strains. The right hand figure shows that across study sites, parasites matched to the vaccine strain (3D7) are overrepresented among the control group, indicating that the vaccine better protected against infection by 3D7 than against other strains. Proper statistical analysis shows that there was a 1-year vaccine efficacy of 50% against strains perfectly matched to the vaccine antigen and a 1-year vaccine efficacy of 33% against unmatched strains. The vaccine strain 3D7 is at low (~10%) frequency in Sub-Saharan Africa. This suggests that vaccine efficacy could be straight-forwardly improved by just swapping 3D7 for a more common haplotype.
It’s interesting to see strain-specific vaccine for malaria, suggesting that like flu, a good vaccine requires matching to the circulating pathogen strains. This was a fun study to participate in. Hopefully, we could see further improvements to the RTS,S vaccine. Even at current efficacy levels, RTS,S is estimated to have a cost effectiveness of ~$150 per disability-adjusted life year saved.