An experimental malaria vaccine appears to offer protection against infection in healthy adults, according to U.S. researchers. The researchers also say
early results indicate the vaccine is safe and “generated an immune response” in the group of volunteers tested.
The vaccine, known as PfSPZ, is composed of live but weakened sporozoites of the species Plasmodium falciparum, the most deadly of the malaria-causing parasites.
Malaria is transmitted to humans by the bite of an infected mosquito. After the bite occurs, infectious malaria parasites in the immature, sporozoite stage of their life cycle, first travel to the liver, where they multiply, and then spread through the bloodstream.
“In this trial, we showed in principle that sporozoites can be developed into a malaria vaccine that confers high levels of protection and is made using the good manufacturing practices that are required for vaccine licensure,” said Dr. Robert A. Seder, chief of the Cellular Immunology Section of the NIAID Vaccine Research Center and principal investigator of the trial.
One potential drawback to the vaccine is that it appeared most effective when administered intravenously because lower doses given under the skin did not yield similar results.
“Despite this challenge, these trial results are a promising first step in generating high-level protection against malaria, and they allow for future studies to optimize the dose, schedule and delivery route of the candidate vaccine,” said Seder.
Fifty-seven adults between 18 and 45 years old took part in Phase One of the trial. Forty received the vaccine and 17 did not. Some of those who received the vaccine were given increasing doses. After seven days of monitoring, “no severe adverse effects associated with the vaccine occurred, and no malaria infections related to vaccination were observed.”
Furthermore, those who received the most vaccine generated more antibodies against malaria, researchers said.
Three weeks after the last dosage, participants -- both those who received the vaccine and the control group -- were exposed to bites from five mosquitoes carrying the P. falciparum strain from which the PfSPZ Vaccine was derived.
The researchers found that the higher dosages of PfSPZ Vaccine were associated with protection against malaria infection. Only three of the 15 participants who received higher doses of the vaccine became infected, compared to 16 of 17 participants in the lower dose group who became infected. Among the 12 participants who received no vaccine, 11 participants became infected, researchers said.
Researchers say they plan several follow-up studies to test dosage schedules and whether larger doses delivered under the skin can offer the same immune response.
“The global burden of malaria is extraordinary and unacceptable,” said Dr. Anthony Fauci, the NIAID director. “Scientists and health care providers have made significant gains in characterizing, treating and preventing malaria; however, a vaccine has remained an elusive goal. We are encouraged by this important step forward.”
The vaccine was developed by scientists at Sanaria Inc. The clinical evaluation was conducted by researchers at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, and their collaborators at the Walter Reed Army Institute of Research and the Naval Medical Research Center.
The results of the study were published in the August 8 issue of Science