According to an early stage clinical trial, published on August 8 in the journal Science, an investigational malaria vaccine has been found safe, to generate an immune system response and to offer protection against malaria in healthy adults.

Known as PfSPZ, the vaccine was developed by scientists at Sanaria Inc. in Rockville, Md. Clinical evaluation of the vaccine was conducted by researchers from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health and collaborators at the Walter Reed Army Institute of Research and the Naval Medical Research, both of which are located in Silver Spring, Md.

Malaria is transmitted to humans through the bite of an infected mosquito. After the bite occurs, malaria parasites in the immature, sporozoite stage of the life cycle first travel to the liver, there they multiply and begin to spread through the bloodstream. This is the time at which symptoms begin to develop.

The PsSPZ vaccine is made with live, but weakened sporozoites of the species Plasmodium falciparum, considered the most deadly of the malaria causing parasites.

“The global burden of malaria is extraordinary and unacceptable,” said NIAID Director Anthony S. Fauci, M.D. “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 Phase I trial took place at the NIH Clinical Center in Bethesda, Md. Consent from 57 healthy adult volunteers between the ages of 18 and 45 who had malaria was received. Of the 57 participants, 40 received the vaccine and 17 did not. To evaluate vaccine safety, participants were split into groups receiving 2 to 6 intravenous doses at increasing dosages. Following the vaccine, participants were monitored for 7 days. No severe reactions were observed and no cases of malaria infection from the vaccine were observed during that time.

“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 Robert A. Seder, M.D., chief of the Cellular Immunology Section of the NIAID Vaccine Research Center and principal investigator of the trial.

One challenge facing the new vaccine is that it must be administered intravenously, a rare form of delivery for vaccines. Previous studies using smaller doses have shown that intradermal and subcutaneous delivery did not yield as strong of an immune response.

“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 Dr. Seder.

A number of follow-up studies have been planned, including one to evaluate different dosing schedules, protection against other strains and durability of protection.