Results from a Phase 1 trial published in Nature Medicine show that an investigational malaria vaccine demonstrated durable protection in healthy, malaria-naive adults in the U.S. from infection for >1 year post-immunization.  

The PfSPZ Vaccine, developed by Sanaria Inc., was evaluated by University of Maryland School of Medicine researchers by immunizing and exposing healthy adult volunteers to the malaria-causing parasite Plasmodium falciparum in a controlled setting. Earlier clinical data showed the vaccine was highly protective 3 weeks post-immunization and so the researchers evaluated whether the protection would last for 5–12 months. 

The Phase 1 trial enrolled 101 healthy adults aged 18–45 years who never had malaria; 59 patients were administered the PfSPZ vaccine and 32 were unvaccinated and served as controls. The vaccinated patients received either three (n=9) or four (n=28) intravenous (IV) immunizations of the vaccine at a higher dose than previously tested in human studies. Eight study patients received 4 immunizations as an intramuscular (IM) injection at a 10-fold higher dose than the IV dose. These groups helped researchers better assess the impact of administration route, dose, and number of immunizations in conferring short- and long-term immunization against malaria

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Both unvaccinated and vaccinated patients were exposed to mosquitoes carrying the same P. falciparum strain from which the vaccine was derived. Short-term protection was studied through patients being bit by the parasite-infected mosquitoes 3 weeks after their final vaccination. Three of the nine patients who received three IV doses were protected or had no detectable parasites in their blood. Seven out of the nine patients who received four IV doses were protected. Just three of the eight patients who received four IM doses were protected; this showed that IV administration provided higher levels of protection at a lower dose. 

Long-term protection was studied through 11 patients who received four IV doses being bit by the parasite-infected mosquitoes 21 weeks after the final vaccination. About 55% (n=6) of patients had no detectable parasites in their blood. Four of these six patients plus one patient who received the same four IV doses (having no parasites in the blood after exposure at 3 and 21 weeks), were bit again at 59 weeks after their final vaccination. Study authors reported all five patients did not develop parasites in their blood whereas all six control patients became infected.

In malaria-naive adults, the PfSPZ vaccine conferred sterile protection for over 1 year in 55% of patients. No serious adverse events were reported and vaccinations were well-tolerated. “Based on the favorable safety profile, we’re testing higher doses in larger trials to see if even greater protection can be achieved long-term against other P. falciparum strains different than the vaccine strain,” noted Robert A. Seder, MD, principal investigator of the trial.

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