RTS,S is the first malaria vaccine candidate that has been shown to have partial efficacy against malaria, but to date, the immune mechanisms responsible for this protection remain unknown. In a three-day meeting held in Barcelona on 29-31 January, 24 representatives from 15 international institutions working on a project aimed at understanding the protective immune responses elicited by the RTS,S vaccine came together to design the next steps of the project. The initiative is being coordinated by the Barcelona Centre for International Health Research (CRESIB) and funded by the US National Institutes of Health (NIH) and the Malaria Vaccine Initiative (MVI), among others.
The experts held several meetings to discuss the strategy for analysing the samples collected in the phase III clinical trial of RTS,S, articulated in three working groups:
The sample analysis plan is based on the successful model employed by the RV144 HIV vaccine, which, using a novel approach, identified two immune responses: one associated with protection against HIV infection and another with increased risk of infection. While the differences between malaria and HIV—and between the two vaccines—are clear, the meeting served to revise the existing strategy and adapt it to the successful approach employed by the RV144 group.
The outcome of the meeting will be reviewed by the scientific leadership committee and presented to the consortium of investigators overseeing the immunological study of the RTS,S vaccine. Once a strategy has been adopted, the next step will be to conduct a pilot study to define and downselect the primary and secondary variables that will be included in the main case-control study of immune correlates of protection induced by the RTS,S vaccine.