WASHINGTON - An experimental anti-malaria vaccine has been developed that protects against more than one strain of the malaria parasite that causes the mosquito-borne illness.
The vaccine, tested by principal investigator Kirsten Lyke and colleagues, is called PfSPZ and uses whole, live weakened early versions of the most common form of malaria Plasmodium falciparum (P. Falciparum), called sporozoites.
This early form of the parasite is what's first injected into humans by an infected mosquito.
By using the entire sporozoite in the vaccine, the immune system responds to more of the parasite, according to Lyke.
15 healthy adults tested
A study of the vaccine conducted by Lyke and colleagues, published in Proceedings of the National Academy of Sciences, enrolled 15 healthy adults who were assigned to receive three doses of the vaccine over several months.
Nineteen weeks after receiving the final dose, the volunteers were exposed to bites of mosquitoes carrying one strain of parasite from Africa.
A second group of six controls that was not vaccinated also got exposed to the mosquitoes. They showed signs of malaria and were promptly treated.
Nine of 14 vaccinated participants, or 64 percent, showed no signs of infection after exposure.
Of the nine, six participants were selected and exposed to a different strain, 33 weeks after the final immunization.
This time, five of the six were protected against this second strain, according to Lyke.
'Great' is not good enough
“Which is great, but not good enough,” said Lyke. “I mean, you don't want to take a vaccine that's going to give you a two out of three chance of being protected. So we have to improve on that and get it up to as close to 100 percent as we can. But at least we've established that we can get very high protection in six months and we're seeing cross-strain protection.”
The agent would offer broader protection against a disease that kills mostly young children in sub-Saharan Africa.
According to the World Health Organization, 212 million people were infected with the mosquito-carrying parasite in 2015, and 429,000 died.
There are four types of malaria parasite that typically infect people. The most common and deadly is Plasmodium falciparum, which goes through a number of life-cycle stages during which the parasite evolves into a different form.
That is what makes it difficult to develop a vaccine.
Multiple strains a problem
The problem is further complicated by the fact that P. falciparum can mutate and develop into multiple strains.
Lyke said this is particularly true in Africa, in places where the disease is common.
“The falciparum malaria that is so endemic, there's a lot of genetic change that occurs because it's so prevalent in the population. And that contributes to different strains of the falciparum malaria so that you know any vaccine that we'd want to introduce we would want to make sure that it broadly covers multiple different strains of falciparum malaria,” Lyke said.
Clinical trials of the early vaccine, produced by the company Sanaria, also are going on in Africa, including in Burkina Faso, Kenya and Bioko Island off of Africa’s west coast.