Investigational Malaria Vaccine May Protect Healthy Adults for More Than One Year

Phase I clinical trials of an investigational Malaria vaccine revealed that it has the potential to protect healthy US adults, who have not been exposed to Malaria before, for more than one year. According to the National Institute of Allergy and Infectious Diseases (NIAID), researchers at the University of Maryland School of Medicine in Baltimore and NIAID conducted a clinical evaluation of the Malaria vaccine, PfSPZ, which involved immunization and exposing willing healthy adults to the malaria-causing parasite Plasmodium falciparum (P. falciparum) in a controlled setting. PfSPZ was developed and produced by Sanaria Inc, with support from several Small Business Innovation Research (SBIR) awards from NIAID, the organization wrote in a press announcement.

The Phase I trial was conducted at the National Institutes of Health (NIH) Clinical Center in Bethesda, Maryland. The study included 101 healthy adults ranging in age from 18–45 years who had never had Malaria. A total of 59 adults received the PfSPZ vaccine, while 32 served as control and were not vaccinated. Vaccine recipients were divided into several groups to assess the roles of administration, dose, and number of immunizations in conferring short- and long-term protection against the disease. To determine if the number of immunizations influenced protection against Malaria, vaccinated participants received either three or four intravenous immunizations of the PfSPZ vaccine at a higher dose than tested in previous human studies. All participants were exposed to the bites of mosquitoes carrying the P. falciparum strain.

To assess long-term protection, an additional group of 11 participants received four IV doses of the investigational vaccine and were exposed to the bites of malaria parasite-infected mosquitoes 21 weeks after their final vaccination. Scientists found that 6–11 participants (55%) had no detectable parasites in their blood after this exposure. Four of these six participants, plus one of the participants who received the same four doses via IV and had no parasites in the blood after exposures at three weeks and 21 weeks, were exposed to mosquito bites again at 59 weeks after their final vaccination. All five participants exposed at 59 weeks did not develop parasites in their blood, while all six unvaccinated control participants became infected with malaria parasites.

Collectively, the data showed that the PfSPZ vaccine provided malaria protection for more than one year in 55% of people without prior malaria infection. In those individuals, the PfSPZ vaccine appeared to confer sterile protection, meaning the individuals would be protected against disease and could not further transmit malaria. There were no serious adverse events attributed to vaccination. Additional results showed that antibodies may play a role in malaria protection early after the final immunization, but inducing T cells in the liver is likely necessary for durable protection. The results of the study were published in Nature Medicine.

Source: NIH