Recent investigations supported by the National Institutes of Health (NIH) into an experimental malaria vaccine in healthy Malian adults demonstrated that all three tested methods were safe. One of the studies involved 300 healthy women aged between 18 and 38 who were expecting to become pregnant shortly after receiving the vaccine. The trial commenced with medication to eliminate malaria parasites, followed by three vaccine injections, given over the course of a month, either as a saline placebo or as the experimental vaccine at one of two dosage levels. Notably, both dosage levels of the vaccine candidate provided substantial protection against parasite infection and clinical malaria for up to two years without needing a booster, marking a groundbreaking achievement for malaria vaccines. In an additional analysis of women who became pregnant during the study, the vaccine notably protected them from malaria during pregnancy. If these findings are validated in further clinical studies, the methodology explored in this research could lead to improved strategies for preventing malaria during pregnancy.
Malaria, transmitted by Anopheles mosquitoes, is caused by parasites including the species Plasmodium falciparum (Pf). This disease can affect individuals of any age but poses a particularly high risk to pregnant women, infants, and young children, who are at an increased threat of severe illness. Each year in Africa, malaria in pregnant women is estimated to contribute to 50,000 maternal deaths and 200,000 stillbirths.
The clinical trials were jointly led by researchers from the NIH’s National Institute of Allergy and Infectious Diseases (NIAID) and the University of Sciences, Techniques and Technologies, Bamako (USTTB), in Mali. The vaccine explored in both trials is the PfSPZ Vaccine, a radiation-attenuated formulation based on Pf sporozoites (a phase of the parasite’s life cycle), produced by Sanaria Inc. in Rockville, Maryland. Previous clinical research on the PfSPZ Vaccine has demonstrated its safety, including in malaria-prone regions such as Mali. For instance, findings published in 2022 from a placebo-controlled trial in Burkina Faso indicated that a three-dose regimen of the PfSPZ Vaccine achieved up to 46% efficacy lasting for at least 18 months.
During the first year of this trial, 55 women became pregnant within 24 weeks after their third vaccine injection. Among these participants, the vaccine showed 65% efficacy against parasitemia (both before and during pregnancy) for those who received the lower vaccine dose and 86% for those given the higher dose. In total, among 155 women who became pregnant throughout both years of study, the efficacy was 57% for those receiving the lower dose and 49% for the higher dose group.
Women who received the investigational vaccine at either dosage tended to conceive sooner than those who were given the placebo, although this observation wasn’t statistically significant, according to the researchers. They hypothesize that the PfSPZ Vaccine might help prevent malaria-related early pregnancy losses because the risk of parasitemia during the period surrounding conception was reduced by 65 to 86%.
The researchers highlighted that “Preconception immunization represents a novel strategy to lower mortality risks for women facing malaria during pregnancy.” They aim to further assess the safety of the PfSPZ Vaccine in pregnant women and later evaluate its effectiveness when administered before conception or during pregnancy in larger clinical trials. “Current preventive measures are insufficient in protecting women from malaria during pregnancy,” they stated. “The urgent need for a safe and effective vaccine is clear, and our findings suggest the PfSPZ Vaccine could be a viable option,” they concluded.
The team overseeing the PfSPZ Vaccine Study was led by Alassane Dicko, M.D., from the Malaria Research and Training Center (MRTC) at USTTB in Mali, Stephen L. Hoffman, M.D., from Sanaria Inc., and Patrick E. Duffy, M.D., from the NIAID Laboratory of Malaria Immunology and Vaccinology. Joint co-first authors included Halimatou Diawara, M.D., of MRTC, and Sara A. Healy, M.D., from NIAID.
