Naturally acquired circumsporozoite antibodies and their role in protection in endemic falciparum and vivax malaria.

The role of naturally acquired circumsporozoite (CS) antibodies in protection against falciparum and vivax malaria was evaluated in a group of Thai endemic villagers using a prospective cohort and a case-control study design. There was no evidence of protection by either the presence of positive CS antibody levels at the presumed time of sporozoite exposure or in individuals who persistently had measurable levels of the antibodies. The study defined levels of CS antibodies that were not protective in natural infection.