TROPICAL MEDICINE

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Experimental PFSPZ Malaria Vaccine Provides Durable Protection Against Multiple Strains

 

Malaria is transmitted to humans through the bite of infected mosquitoes, which inject immature malaria parasites called sporozoites into a person’s bloodstream. The parasites travel to the liver, where they mature, multiply and spread via the bloodstream throughout the body causing malaria symptoms including chills, fever, headache, nausea, sweating and fatigue. According to the World Health Organization, 214 million people were infected with malaria globally in 2015 and 438,000 people died, mostly young African children. The species Plasmodium falciparum is the most common cause of malaria morbidity and mortality in Africa. In the United States, travel-related malaria is a concern for international tourists, aid workers and military personnel worldwide.

 

According to an article published in the Proceedings of the National Academy of Sciences (PNAS; 21 Feb 2017), an investigational malaria vaccine has protected a small number of healthy U.S. adults from infection with a malaria strain different from that contained in the vaccine. The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, sponsored and co-conducted the Phase 1 clinical trial.

 

The PfSPZ Vaccine used in this study was developed by Sanaria Inc., of Rockville, Maryland. The vaccine contains weakened P. falciparum sporozoites that do not cause infection but are able to generate a protective immune response against live malaria infection. Earlier research at the NIH Clinical Center with the PfSPZ Vaccine found it to be safe, well-tolerated and protective for more than a year when tested in healthy U.S. adults against a single Africa-derived malaria strain matched to the PfSPZ Vaccine. The study enrolled 31 healthy adults ages 18 to 45 years and each study subject was assigned to receive three doses of the PfSPZ Vaccine at eight-week intervals by rapid intravenous injection. Nineteen weeks after receiving the final dose of the test vaccine, participants who received the vaccine and a group of non-vaccinated volunteers were exposed in a controlled setting to bites from mosquitoes infected with the same strain of P. falciparum parasites (NF54, from Africa) that were used to manufacture PfSPZ Vaccine. Results showed that 9 of the 14 participants (64%) who received PfSPZ Vaccine demonstrated no evidence of malaria parasites, while all 6 of the non-vaccinated participants who were challenged at the same time had malaria parasites in their blood. Of the 9 participants who showed no evidence of malaria, six participants were again exposed in a controlled setting to mosquito bites, this time from mosquitoes infected with a different strain of P. falciparum parasite, 33 weeks after the final immunization. In this group, 5 of the 6 participants (83%) were protected against malaria infection, while again, none of the 6 participants who did not receive the vaccine and were challenged were protected. All participants who became infected with malaria immediately received medical treatment.

 

The authors also found that the PfSPZ Vaccine activated T cells, a key component of the body’s defenses against malaria, and induced antibody responses in all vaccine recipients. Vaccine-specific T-cell responses were comparable when measured against both of the malaria challenge strains, providing some insights into how the vaccine was mediating protection.

 

Ongoing research will determine whether protective efficacy can be improved by changes to the PfSPZ Vaccine dose and number of immunizations.  Accordingly, a Phase 2 efficacy trial testing three different dosages in a three-dose vaccine regimen is now underway in 5-to 12-month-old infants in Western Kenya to assess safety and efficacy against natural infection.

 

Sanaria Inc., designed, manufactured, and provided PfSPZ Vaccine and the heterologous challenge mosquitoes. NIAID supported the development of the experimental vaccine through several Small Business Innovation Research grants.

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