BETHESDA, Md., May 10 (UPI) -- A vaccine against malaria protected healthy people from being infected when exposed to mosquitoes carrying the parasite that causes the disease in a small clinical trial, according to the National Institutes of Health.
University of Maryland researchers treated healthy volunteers in a phase 1 trial with the PfSPZ Vaccine, finding some participants were protected from malaria infection for more than a year, with larger trials now in the works based on its efficacy.
Malaria is spread by mosquitoes carrying the Plasmodium falciparum parasite, causing fever, chills and other flu-like symptoms, and can lead to death if not treated. Although the Centers for Disease Control and Prevention reports there are about 1,500 cases of malaria each year in the United States, there were 214 million worldwide in 2015 and 438,000 deaths, most of whom were children.
The PfSPZ Vaccine contains weakened P. falciparum sporozoites, and was shown in a previous phase 1 trial to prevent malaria infection three weeks after healthy volunteers received it.
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"A malaria vaccine that provides long-term protection is urgently needed to reduce mortality and eliminate transmission," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in a press release. "This study is an encouraging step forward in our goal to control and ultimately eradicate malaria."
For the study, published in the journal Nature Medicine, researchers treated 101 healthy adults between the ages of 18 and 45 who had never had malaria, giving 59 the PfSPZ Vaccine and 32 a placebo before splitting vaccine recipients into groups to test varying locations for injection, dose and number of shots.
Of participants receiving the vaccine, nine were given three shots and 28 received four shots intravenously at higher doses than had previously been tested with humans. Eight participants were given a four-shot series intramuscularly, at a dose 10 times higher than that given intravenously.
Three weeks after receiving their final injection, participants were then exposed to mosquitoes carrying the malaria parasite and had their blood tested. Of nine participants who received three intravenous shots, three had no detectable parasites in their blood; Of the nine given four intravenous shots, seven were protected; and of the eight given intramuscular shots, three were protected.
To assess the vaccine's long-term efficacy, the researchers gave 11 participants four intravenous doses and exposed them to mosquitoes carrying the malaria parasite 21 weeks after their final shot. Blood tests showed six of the 11 had no parasites in their blood. Four of these and one participant from an earlier stage of the trial were exposed to mosquitoes again at 59 weeks and were not infected.
"It is now clear that administering the PfSPZ Vaccine intravenously confers long-term, sterile protection in a small number of participants, which has not been achieved with other current vaccine approaches," Dr. Robert A. Seder, chief of the Cellular Immunology Section of NIAID's Vaccine Research Center, said of the 55 percent protection rate in the phase 1 trial. "Based on the favorable safety profile, we're testing higher doses in larger trials to see if even greater protection can be achieved long-term against other P. falciparum strains different than the vaccine strain."
