IMPACT OF TRANSMISSION INTENSITY AND AGE ON PLASMODIUM-FALCIPARUM DENSITY AND ASSOCIATED FEVER - IMPLICATIONS FOR MALARIA VACCINE TRIAL DESIGN

To facilitate design of vaccine trials, malaria was studied in 6-month - to 6-year-oId Kenyans during high (HI) and low intensity transmissio n seasons, During 84 days after cure, exposure to infected mosquitoes was 9-fold greater in the HI group, yet incidence of P. falciparum inf ection was increased only 2-fold, with no age effect. The density of r ecurrent P. falciparum was 14-fold greater in the HI group, and there was a striking association between age and parasitemia greater than or equal to 5000/mu L. Fever was the only clinical manifestation attribu table to parasitemia and only when the parasite density was greater th an or equal to 5000/mu L. Sixty-four percent of children with greater than or equal to 20,000 parasites/mu L versus 10% with 1-4999/mu L wer e febrile when parasitemic. Recurrent P. falciparum infection as a vac cine trial end point can be studied year-round among children greater than or equal to 6 years in western Kenya. However, high-grade parasit emia (greater than or equal to 5000 or 20,000/mu L) with or without el evated temperature will be optimally studied in the high transmission season among children <2 years.