A promising new malaria vaccine has shown unprecedented efficacy in early-stage trials, according to the US National Institutes of Health (NIH).
The vaccine – which is based on a live, weakened strain of the Plasmodium falciparum parasite that causes the most deadly form of the disease – protected 12 out of 15 patients exposed to a controlled malaria infection in the phase I trial.
At the highest dose tested, vaccination with the PfSPZ shot provided complete protection against malaria in six patients. Three cases of malaria were seen among nine patients given a lower dose, while five out of six unvaccinated controls developed the disease, according to the researchers, who have published the results in Science magazine.
The researchers found that participants who received a higher total dosage of PfSPZ generated more antibodies against malaria and more T lymphocytes specific to the vaccine. It was administered as four intravenous injections at monthly intervals with a final injection given eight weeks later.
“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 the trial’s principle investigator, Robert Seder of the US National Institute of Allergy and Infectious Diseases (NIAID).
The results of the NIH-backed study have thrown the US biotech behind the vaccine – Rockville, Maryland-based Sanaria – into the spotlight, although chief executive Stephen Hoffman stressed the development work is still in the early stages.
“There is still much work to do and our efforts must continue for some time to come before we reach the target of licensing, commercialising and deploying an effective malaria vaccine,” said Hoffman.
For instance, at the moment the vaccine has to be administered intravenously, which is not really suitable for widespread vaccination programmes. Previous studies have showed that subcutaneous and intradermal administration of PfSPZ is not as effective, although these used lower doses than in the latest phase I trial.
The researchers are now considering studies to see if higher doses given subcutaneously or intradermally can be effective, and also to test other dosing schedules to see how durable the protection is over time.
“We think that the timing of administration will be very important,” said Hoffman, noting that the overall aim will be to try to simplify the administration regimen as much as possible.
“We believe this vaccine will be used to eliminate malaria,” he said, adding: “It’s reasonable to suggest that within three-to-five years, a safe, reliable vaccine could be a commercial reality and provide medical benefit to a huge population.”
In 2010, malaria caused an estimated 660,000 deaths, mostly among African children, according to the World Health Organization (WHO), which notes that around 219 million people contracted the disease in the same year.
While preventable and treatable with antimalarial drugs, access to medicines is problematic in many areas of the world and complicated by increasing resistance which may be related in part to medicines counterfeiting.
Efforts to develop an effective vaccine have met with limited success to date. Last November, a malaria vaccine called RTS,S/AS01 developed by GlaxoSmithKline (GSK) – considered by the WHO to be the furthest ahead in development, showed modest efficacy in a paediatric trial.
RTS,S/AS01 reduced clinical malaria episodes by around a third overall, but with markedly different activity depending on the children’s age group. A large-scale trial of this vaccine is still ongoing and is due to report results in late 2014.