NIH Trials Show Long-lasting Protection from Malaria Vaccine

On August 14, 2024, the National Institutes of Health (NIH) disclosed findings from two significant trials involving an experimental malaria vaccine, conducted in healthy adults in Mali. Both trials confirmed the vaccine's safety across all tested regimens. One trial specifically targeted 300 healthy women, aged 18 to 38, who were expected to become pregnant shortly after receiving the vaccine. This trial started with malaria drug treatment to clear any existing parasites, followed by three immunizations over a month with either a saline placebo or the investigational vaccine at two different doses. Remarkably, both dosages conferred substantial protection against malaria and parasite infection for two years, without the need for a booster shot—an unprecedented outcome for malaria vaccines. Additionally, an exploratory analysis indicated the vaccine's significant protection for women who conceived during the study from malaria during pregnancy. If validated by further clinical trials, this approach could potentially enhance malaria prevention strategies during pregnancy.

Malaria, transmitted by Anopheles mosquitoes, can cause serious illness in people of any age, but it is particularly dangerous for pregnant women, infants, and young children. Each year in Africa, malarial parasitemia during pregnancy is estimated to result in up to 50,000 maternal deaths and 200,000 stillbirths.

The trials were collaboratively led by researchers from NIH’s National Institute of Allergy and Infectious Diseases (NIAID) and the University of Sciences, Techniques and Technologies of Bamako (USTTB) in Mali. The experimental vaccine, known as PfSPZ Vaccine, is developed by Sanaria Inc., based in Rockville, Maryland. This vaccine is a radiation-attenuated formulation derived from Plasmodium falciparum sporozoites, a specific stage of the malaria parasite's lifecycle. Prior clinical trials have established the vaccine's safety, including studies conducted in malaria-endemic regions like Mali. In 2022, an NIAID-sponsored, placebo-controlled trial in Burkina Faso demonstrated the vaccine's efficacy of up to 46%, lasting for at least 18 months.

In the ongoing trials, during the first year, 55 women became pregnant within 24 weeks of receiving the third vaccine dose. Among these participants, vaccine efficacy against parasitemia was 65% for those administered the lower dose and 86% for those given the higher dose. During the two-year study period, 155 women became pregnant, with a vaccine efficacy of 57% for the lower dose and 49% for the higher dose group.

Interestingly, women who received the vaccine, regardless of the dosage, tended to conceive sooner than those who received the placebo, although this observation did not reach statistical significance. The researchers theorize that the PfSPZ Vaccine might reduce early pregnancy losses related to malaria, as parasitemia risk during the periconception period was lowered by 65 to 86%.

The researchers view preconception immunization as a novel strategy to reduce mortality from malaria during pregnancy. Future plans include investigating the safety of the PfSPZ Vaccine during pregnancy and further evaluating its efficacy when administered preconception or during pregnancy in larger clinical trials. They emphasize the urgent need for a safe and effective malaria vaccine, as current measures are inadequate for protecting pregnant women from the disease.

The PfSPZ Vaccine Study Team comprised Alassane Dicko, M.D., from the Malaria Research and Training Center (MRTC) at USTTB, Stephen L. Hoffman, M.D., from Sanaria Inc., and Patrick E. Duffy, M.D., from the NIAID Laboratory of Malaria Immunology and Vaccinology. The study’s joint first authors were Halimatou Diawara, M.D., from MRTC, and Sara A. Healy, M.D., from NIAID.

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