Two NIH-supported trials of the PfSPZ Vaccine, an experimental malaria vaccine, have shown promising results in providing lasting protection against malaria in healthy Malian adults. The trials, conducted in Mali, Africa, demonstrated that all three tested regimens were safe and conferred a significant degree of protection from parasite infection and clinical malaria for up to two years without needing a booster dose. This marks a significant advancement in malaria vaccine development.
Trial Design and Results
The trials enrolled 300 healthy women ages 18 to 38 who anticipated becoming pregnant. Participants received either a saline placebo or one of two dosages of the investigational vaccine over a month, following drug treatment to remove existing malaria parasites. The results indicated that both dosages of the vaccine candidate provided substantial protection against parasite infection and clinical malaria, which was sustained over two years.
In an exploratory analysis of women who conceived during the study, the vaccine significantly protected them from malaria in pregnancy. Specifically, among women who became pregnant within 24 weeks of the third vaccine dose, vaccine efficacy against parasitemia was 65% in those who received the lower dose and 86% in those who received the higher dose. Among 155 women who became pregnant across both study years, vaccine efficacy was 57% for those who received the lower dose vaccine and 49% in those in the higher dosage group.
Implications for Malaria Prevention
Malaria, spread by Anopheles mosquitoes, poses a significant threat, particularly to pregnant women, infants, and young children. Malarial parasitemia in pregnancy is estimated to cause up to 50,000 maternal deaths and 200,000 stillbirths in Africa annually. The current findings suggest that preconception immunization with PfSPZ Vaccine could be a viable strategy to reduce mortality for women with malaria in pregnancy.
Researchers speculate that the PfSPZ Vaccine might avert malaria-related early pregnancy losses, as parasitemia risk during the periconception period was reduced by 65 to 86%. However, the investigators reported that women who received the investigational vaccine at either of the dosages conceived sooner than those who received placebo, although this finding did not reach the level of statistical significance.
Future Directions
The researchers plan to further investigate the safety of PfSPZ Vaccine administered during pregnancy and examine its efficacy in larger clinical trials, both preconception and during pregnancy. According to the researchers, "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."
The investigational vaccine, PfSPZ Vaccine, is a radiation-attenuated vaccine based on Plasmodium falciparum (Pf) sporozoites, manufactured by Sanaria Inc. Previous trials have shown it to be safe in malaria-endemic countries. A prior NIAID-sponsored trial in Burkina Faso found that a three-dose regimen of PfSPZ Vaccine had up to 46% efficacy lasting at least 18 months.
