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Vaccine Shown to Give 1-Year Malaria Protection

Anopheles mosquito

Anopheles mosquito that spreads malaria parasite with blood from a human (William Collins, CDC)

10 May 2016. An early-stage clinical trial with healthy volunteers shows an experimental vaccine can protect against malaria infection for as long as 1 year. Results of the trial, conducted by National Institute of Allergy and Infectious Diseases, or NIAID, part of National Institutes of Health, and University of Maryland Medical Center in Baltimore, appear in yesterday’s issue of the journal Nature Medicine (paid subscription required).

The study tested a malaria vaccine, code-named PfSPZ, made by Sanaria Inc. in Rockville, Maryland. Malaria is caused by infections from the Plasmodium parasite transmitted by mosquitoes. In humans, the parasite multiplies in the liver, then infects red blood cells. Symptoms, including headache, fever, and vomiting, occur 10 to 15 days following transmission from a mosquito bite. World Health Organization says the disease occurs in nearly 100 countries, with some 214 million cases in 2015, causing up to 438,000 deaths.

Sanaria is a biotechnology company developing PfSPZ with live, but weakened Plasmodium sporozoites, an early spore-like form of the parasite. NIAID provided Sanaria part of its funding for the vaccine through a series of Small Business Innovation Research grants. University of Maryland’s vaccine development center is a collaborator on the design and development of the vaccine, as well as testing.

The clinical trial tested the vaccine among healthy volunteers with no previous exposure to malaria. The volunteers received injections in veins or muscles of PfSPZ to evaluate the effectiveness the delivery method, numbers of immunizations, and length of protection time. Most of the volunteers (59) received the vaccine, while some (32) were left unvaccinated for comparison.

Participants in the trial were exposed to 5 malaria-carrying mosquitoes in a cup, placed on the arm until all 5 bit the participant. All trial participants visited clinics frequently, and those contracting malaria were treated immediately, a process taking some 72 hours. These procedures say the researchers, carried out at Walter Reed Army Institute of Research in Silver Spring, Maryland, are standard methods for early-stage malaria vaccine trials.

At 3 weeks after receiving the vaccine, participants gave blood samples to evaluate the amount of parasite infection. The results show participants receiving 4 rather than 3 injections, and those injecting through veins rather than muscles, were better protected against infections.

The researchers then tested the vaccine’s effectiveness for 21 and 59 weeks with 11 participants who received 4 intravenous injections of PfSPZ. The 11 participants were exposed to mosquito bites at 21 weeks after the injections, and 6 of the 11 participants were found with no parasite infections in their blood. After 59 weeks, 5 participants — 4 of the 6 receiving intravenous injections plus 1 with a muscle injection, all of whom had no parasites in their blood — continued to show no sign of malaria infections.

The researchers say antibody levels dropped in participants’ blood samples along with T-cell responses to the parasites by 59 weeks, suggesting the vaccines provide durable protection against malaria. In addition, the vaccines were well-tolerated, with no serious adverse effects linked to the vaccinations.

“We intend to use PfSPZ vaccine for preventing malaria in individuals, halting transmission of the malaria parasite and eliminating the parasite through mass vaccine administration campaigns,” says Sanaria CEO Stephen Hoffman in a company statement.  “It’s reasonable to suggest that within three-to-four years a safe, reliable vaccine could be a commercial reality and provide medical benefit to a huge population.”

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