New malaria vaccine

Print edition : September 06, 2013

Anopheles gambiae mosquito feeds on a human host. Photo: Centre for Disease Control (CDC), Jim Gathany

AN investigational malaria vaccine has been found to be safe to generate an immune system response and to offer protection against malaria infection in healthy adults, according to the results of an early-stage clinical trial published recently in the journal Science.

The vaccine, known as PfSPZ Vaccine, was developed by scientists at Sanaria Inc. in Rockville, Maryland. The clinical evaluation was conducted by researchers at the National Institute of Allergy and Infectious Diseases (NIAID) and their collaborators at the Walter Reed Army Institute of Research and the Naval Medical Research Centre.

After a mosquito bite, infectious malarial parasites in the immature, sporozoite stage of their life cycle first travel to the liver, where they multiply, and then spread through the bloodstream, at which time symptoms develop.

PfSPZ Vaccine is composed of live but weakened sporozoites of the species Plasmodium falciparum, the most deadly of malaria-causing parasites.

The Phase I trial enrolled 57 healthy adult volunteers, aged 18 to 45 years, who never had malaria. Of these, 40 participants received the vaccine (receiving two to six intravenous dosages) and 17 did not. After vaccination, participants were monitored closely for seven days. No severe adverse effects associated with the vaccine occurred, and no malaria infections relating to vaccination were observed.

On the basis of blood measurements, researchers found that participants who received a higher total dosage of PfSPZ Vaccine generated more antibodies against malaria and more T-cells—a type of immune system cell—specific to the vaccine.

To evaluate whether and how well PfSPZ Vaccine prevented malaria infection, each participant—the vaccinees as well as the control group—was exposed to bites by five mosquitoes carrying the P. falciparum strain. This controlled human malaria infection procedure took place three weeks after the participants received their final vaccination.

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 dosages of the vaccine became infected, compared with 16 of 17 participants in the lower dosage group who became infected.

Among the 12 participants who received no vaccine, 11 participants became infected after the mosquito challenge.

An important challenge in the continued development of PfSPZ Vaccine is that the vaccine currently is administered intravenously—a rare delivery route for vaccines. Previous studies at lower doses have shown that the more common intradermal (into the skin) and subcutaneous (under the skin) routes did not yield as strong an immune response as the intravenous route.

As part of the planned follow-up studies, the researchers may also evaluate whether higher doses administered subcutaneously or intradermally provide the same level of protection.

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