Experimental Malaria Vaccine Found to be Safe in Multiple Trials in Mali

A National Institutes of Health (NIH) press release on Aug. 14, 2024 announced that two NIH-supported trials found an experimental vaccine for malaria, PfSPZ, to be safe for use in adults in the African country of Mali (1). The findings of the trials, which tested healthy adults and, separately, healthy women of childbearing potential, were published in The Lancet Infectious Diseases (2–4).

PfSPZ, manufactured by Rockville, Md.-based Sanaria, is a radiation-attenuated vaccine based on the sporozites stage of the Plasmodium falciparum (Pf) malaria parasite. Pf is among the species of malaria parasites spread by Anopheles mosquitoes and can cause illness at any age; although, the risk of life-threatening disease is most pronounced in pregnant women, infants, and very young children, according to NIH (1). The press release added that as many as 50,000 maternal deaths and 200,000 stillbirths annually in Africa can be attributed to malarial parasitemia in pregnancy.

With that in mind, one of the trials led by NIH’s National Institute of Allergy and Infectious Diseases, in tandem with the University of Sciences, Techniques and Technologies of Bamako in Mali, enrolled 300 healthy women from age 18 to 38 who anticipated becoming pregnant soon after immunization (1). Malaria parasites were first removed with drug treatment, and then a three-injection regimen followed—with both of two different dosages showing protection for a period of two years without need of a booster dose, something NIH said was a first for a malaria vaccine.

In the first year of this trial, NIH said, 55 women became pregnant within 24 weeks of their third vaccine dose, and vaccine efficacy in that group ranged from 65% in those who received a lower dose vaccine to 86% in those who got a higher dose (1). Somewhat on the contrary, in 155 women who got pregnant over the full two-year study period, efficacy was 57% in the lower dose group and 49% for the higher.

Although researchers said it did not reach the level of statistical significance, women who got the vaccine at either dose conceived earlier than those who received a placebo, leading the researchers to conclude that PfSPZ might help avert malaria-related early pregnancy loss, as parasitemia risk in the periconception period was reduced by between 65% to 86% (1).

“Preconception immunization is a new strategy to reduce mortality for women with malaria in pregnancy,” the researchers were quoted as saying in the press release. “Existing measures are not protecting women from malaria in pregnancy…A safe and effective vaccine is urgently needed, and our results indicate PfSPZ Vaccine might be a suitable candidate.”

References

1. National Institutes of Health. Candidate Malaria Vaccine Provides Lasting Protection in NIH-Sponsored Trials. Press Release. Aug. 14, 2024.
2. Diawara, H.; Healy, S.A.; Mwakingwe-Omari, A.; et al. Safety and Efficacy of PfSPZ Vaccine Against Malaria in Healthy Adults and Women Anticipating Pregnancy in Mali: Two Randomised, Double-Blind, Placebo-Controlled, Phase 1 and 2 Trials. Lancet Infect. Dis. 2024 (online). DOI: 10.1016/S1473-3099(24)00360-8
3. National Library of Medicine. Safety, Immunogenicity, and Protective Efficacy of Two Regimens of Radiation Attenuated Plasmodium Falciparum NF54 Sporozoites (PfSPZ Vaccine) During Natural Transmission Season in Healthy African Adults in Mali. ClinicalTrials.gov, Aug. 20, 2021 (accessed Aug. 15, 2024).
4. National Library of Medicine. Safety, Immunogenicity, and Protective Efficacy of Radiation Attenuated Plasmodium Falciparum NF54 Sporozoites (PfSPZ Vaccine) During Malaria Transmission Season in Healthy African Adult Women of Childbearing Potential in Mali. ClinicalTrials.gov, March 19, 2024 (accessed Aug. 15, 2024).