A human trial for a malaria vaccine has achieved up to 100% protection against infection (by the same strain used in the vaccine) for at least 10 weeks after the last dose. The trial, published online in Nature this week, tested the vaccine in a total of 35 human participants and found no severe side effects to the treatment. Further optimization of the treatment is needed before it can be determined whether the approach will be suitable for the development of a vaccination programme to prevent malaria.
Some of the highest levels of protection against malaria reported to date have been achieved with vaccination strategies that use either infectious or attenuated Plasmodium falciparum sporozites (PfSPZ), cells from the malaria-causing parasite, to elicit an immune response. Previous efforts have used mosquitoes to deliver live PfSPZ, but Stephen Hoffman and colleagues investigate direct venous inoculation of infectious PfSPZ, which is a more practical mode of delivery in clinical settings. Healthy volunteers were given varying doses of the vaccine alongside chloroquine, an antimalarial drug, and were then infected with the same strain of malaria used in the vaccine. When delivered in three doses at four-week intervals, the lower doses only protected some of the participants against infection, but the highest dose achieved 100% protection (in nine participants) for at least 10 weeks after the last dose. The same high dose delivered at shorter time period (three doses at five-day intervals) protected five out of eight individuals (63%).
The authors note that further investigations are needed to determine whether their vaccine might have the potential to be useful as part of mass vaccination strategies to prevent malaria. They propose that their next clinical trials will assess how effective their vaccine could be in more diverse populations, whether it works for different forms of malaria exposure and in different strains of the disease, and what the duration of protection might be.