Keywords: malaria vaccines, Plasmodium falciparum, endemic countries, children, pregnant women, asexual blood stages, stable parasite transmission, protective immunity, asymptomatic parasitaemia, variable surface antigens, VSA
Developing Plasmodium falciparum malaria vaccines for populations living in areas with stable parasite transmission
Individuals living in areas with stable transmission of Plasmodium falciparum parasites develop substantial protective immunity to the disease during childhood. Because of naturally acquired immunity, which appears mainly to target parasite-encoded Variable Surface Antigens (VSA) on the Infected Erythrocytes (IE), severe and life-threatening disease among adults in such areas is rare. However, low-grade asymptomatic parasitaemia continues to be present in a large proportion of people. So far, experimental P. falciparum malaria vaccination employing non-VSA antigens have resulted in variable degrees of protection, including sterile protection, but the duration of the protection afforded is short-lived, probably due to insufficient boosting. Based on these findings, our approach to vaccine development is to accelerate naturally acquired VSA-specific immunity. The ambition is to develop vaccines that will protect against mortality and severe morbidity, but which allow persistence of low-grade, asymptomatic infection. Hopefully, this approach will ensure regular boosting of immunity that appears necessary for the long-lasting protection required of vaccines to be deployed in malaria-endemic areas.