A novel approach to finding an effective malaria vaccine is showing promise against the disease, a team of government, academic, and private researchers reported in a study published Thursday in the journal Science.
In 2010 an estimated 200 million people were infected with malaria, and as many as 1.24 million deaths were reported.
In an early-stage trial, the so-named PfSPZ vaccine protected against malaria infection in all of the six volunteers who received the five dose, and protected six of the nine volunteers who received four doses. In contrast, five of six unvaccinated participants became infected with the disease.
“Clearly the results that these authors obtained are really very impressive. For those individuals receiving five doses, they are recording 100 percent protection,” says Nirbhay Kumar, chair of the Department of Tropical Medicine at Tulane University School of Public Health and Tropical Medicine in New Orleans, who is working on a different kind of vaccine that would prevent mosquitoes from transmitting the Plasmodium parasites that cause malaria. That level of protection is the highest seen so far in any malaria vaccine trial.
But the published study involved a Phase I clinical trial, the first step in human testing, and the number of subjects is very small. This is just the beginning of the research need to determine if the malaria vaccine could ever be of practical use, says Kumar.
Dr. Anthony Fauci, an immunologist and director of the National Institute of Allergy and Infectious Diseases (NIAID), where the clinical trial took place, agrees. “There is a lot more work to be done,” he says. Fauci calls the results “an important proof of concept that a very high degree of efficacy can be attained by this product.”
The PfSPZ vaccine researchers chose to use the whole parasite rather than just a protein because, for 40 years, scientists have known that strong, sustained immunity could be achieved by exposing human volunteers to the bites of irradiated, infected mosquitos. But “it took up to 1,000 mosquito bites to confer high-level protection,” said lead author Dr. Robert Seder, Chief of the Cellular Immunology Section at the Vaccine Research Center within NIAID, in a Science podcast.
Unlike most vaccines, that are injected into the skin, this vaccine is delivered directly into the vein. For small populations such vaccines can be easily used, but for mass vaccination program the logistics are complicated. More research is being done on whether higher doses using standard injection might achieve the same results. Future studies will also address whether the vaccine will work against multiple strains of the parasite that exist in the wild.
Many questions will need to be answered before the malaria vaccine can be put to use in the field, but the critical question is how long does the immunity last.
“Historically, if you really get a vaccine that works, and you can really get it administered widely, that’s the way you control, eliminate and even eradicate certain diseases,” says Fauci.