A malaria vaccine has become the first to provide 100% protection against the disease, confounding critics and far surpassing any other experimental malaria vaccine tested. It will now be tested further in clinical trials in Africa.
The results are important because they demonstrate for the first time the concept that a malaria vaccine can provide a high level of protection, says Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, adding that the findings are cause for "cautious optimism".
No effective malaria vaccine is available at present. The World Health Organization has set a target to develop a malaria vaccine with 80% efficacy by 2025, but until now, says Fauci, "we have not even gotten anywhere near that level of efficacy."
Scientists had previously been sceptical of the vaccine because producing it required overcoming massive logistical hurdles. The vaccine — called PfSPZ because it is made from sporozoites (SPZ), a stage in the life cycle of the malarial parasite Plasmodium falciparum (Pf) — uses a weakened form of the whole parasite to invoke an immune response.
In the phase I safety trial, reported today in Science1, the six subjects given five doses intravenously were 100% protected from later challenge by bites of infectious mosquitoes, whereas five of six unvaccinated controls developed malaria — as did three of nine people given only four doses of the vaccine.
PfSPZ was developed by Sanaria, a company based in Rockville, Maryland, and led by Stephen Hoffman, a veteran malaria researcher who also led the PfSPZ clinical trial. Most malaria-vaccine candidates are recombinant-subunit vaccines containing just a handful of parasite proteins, but Hoffman decided to test the whole-sporozoite vaccine on the basis of past experiments dating back to the 1970s showing that strong and long-lived protection could be obtained by exposing volunteers to thousands of bites from irradiated infected mosquitoes2.
That the vaccine works so well is a "pivotal success," says Stefan Kappe, a malaria researcher at the Seattle Biomedical Research Institute in Washington."The trial results constitute the most important advance in malaria vaccine development since the first demonstration of protection with radiation attenuated sporozoite immunization by mosquito bite in the 70s."