Two Phase 1 clinical trials, conducted in the US, of a novel candidate malaria vaccine, have found that the regimen conferred unprecedentedly high levels of durable protection when volunteers were later exposed to disease-causing malaria parasites.
The researchers have said that the vaccine combines live parasites with either of two widely used antimalarial drugs — an approach termed chemoprophylaxis vaccination. They also added that a Phase 2 clinical trial of the vaccine is now underway in Mali, a malaria-endemic country.
The Sanaria vaccine, called PfSPZ, is reported to be composed of sporozoites, the form of the malaria parasite transmitted to people by mosquito bites. Sporozoites travel through the blood to the liver to initiate infection.
In the phase 1 trials, the researchers said, healthy adult volunteers received PfSPZ along with either pyrimethamine, a drug that kills liver-stage parasites, or chloroquine, which kills blood-stage parasites.
The scientists added that three months later, that the volunteers were exposed to either an African malaria parasite strain that was the same as that in the vaccine (homologous challenge) or a variant South American parasite (heterologous challenge) that was more genetically distant from the vaccine strain than hundreds of African parasites.
The trial results showed that seven out of eight volunteers (87.5%) who received the highest PfSPZ dosage combined with pyrimethamine were protected from homologous challenge, and seven out of nine volunteers (77.8%) were protected from heterologous challenge.
It also showed the highest efficiency in the case of the chloroquine combination, where all six volunteers (100%) who received the higher PfSPZ dosage were completely protected from heterologous challenges.
The authors of the study noted that the high levels of cross-strain protection lasted at least three months (the time elapsed between vaccination and challenge) for both higher-dose regimens. “One hundred per cent protection for three months against heterologous variant parasites is unprecedented for any malaria vaccine in development.”