Photo by James Gathany
A new malaria vaccine candidate proved partially effective in adult males living in an area of low malaria transmission.
The T-cell vaccine consists of the recombinant viral vectors chimpanzee adenovirus 63 (ChAd63) and modified vaccinia Ankara (MVA), both encoding the multiple epitope string and thrombospondin-related adhesion protein (ME-TRAP), a fusion of protein fragments found on the surface of the malaria parasite Plasmodium falciparum.
In what’s known as a prime-boost strategy, an initial dose of the vaccine “primes” the immune system by exposing it to the malaria antigen and is followed by a vaccine booster, which re-stimulates the immune system to further solidify immunity.
Caroline Ogwang, of the Kenya Medical Research Institute–Wellcome Trust Research Programme in Kilifi, Kenya, and her colleagues described their trial of the vaccine in Science Translational Medicine.
The researchers tested the vaccine in an area of low malaria transmission in Kenya. They enrolled 121 healthy adult men and randomized them to receive the malaria vaccine or a control rabies vaccine.
The subjects were also treated with antimalarial drugs to clear any previous infection and were closely monitored for 8 weeks for P falciparum infection.
The malaria vaccine appeared to be safe, prompting no serious adverse events. The most common local adverse event associated with both ChAd63 ME-TRAP and MVA ME-TRAP was mild to moderate pain that lasted from a few hours to 3 days.
Subjects also experienced various systemic adverse events of mild to moderate intensity that lasted from a few hours to 5 days. Other events were reported within 30 days of vaccination as well, but these were not considered vaccine-related.
As for efficacy, blood tests revealed that the vaccine activated a strong immune response from T cells. For at least 2 weeks after vaccination, the vaccine showed partial efficacy in protecting against malaria infection.
The vaccine reduced subjects’ risk of infection by 67% (P=0.002) during the 8-week monitoring period. And the researchers said T-cell responses to TRAP peptides 21 to 30 were significantly associated with protection (hazard ratio=0.24, P=0.016).
The team is continuing clinical testing of the vaccine, including possible combinations with other vaccination strategies to increase efficacy.
