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 transmission seasons, During 84 days after cure, exposure to infected mosquitoes was 9-fold greater in the HI group, yet incidence of P. falciparum infection was increased only 2-fold, with no age effect. The density of recurrent 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 attributable to parasitemia and only when the parasite density was greater than 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 were febrile when parasitemic. Recurrent P. falciparum infection as a vaccine trial end point can be studied year-round among children greater than or equal to 6 years in western Kenya. However, high-grade parasitemia (greater than or equal to 5000 or 20,000/mu L) with or without elevated temperature will be optimally studied in the high transmission season among children <2 years.