PHASE-I TRIAL OF THE SPF66 MALARIA VACCINE IN A MALARIA-EXPERIENCED POPULATION IN SOUTHEAST-ASIA

In preparation for a recently reported, independent field trial of SPf 66 malaria vaccine efficacy in Thailand, we first established the safe ty and immunogenicity of two clinical lots of U.S. manufactured lots o f SPf66 in a series of overlapping Phase I studies. The vaccine was pr oduced in approved laboratories using good manufacturing practices. Tw o clinical lots of alum-adsorbed SPf66 were evaluated in a combined, o pen-label, Phase I clinical trial involving 50 healthy, malaria-experi enced Karen adults and children. Volunteers were grouped by age and im munized sequentially. Group 1 had 30 adults, Group 2 had 10 children 8 -15 years of age, and Group 3 had 10 children 2-6 years of age. The SP f66 vaccine was well tolerated in this malaria-experienced population. The most common side effects were erythema, induration, warmth, and t enderness at the site of injection, which typically resolved within 24 -48 hr. One adult volunteer developed an acute urticarial rash followi ng the third dose. Among adults, and to a lesser extent older children , females had more local reactions than their male counterparts. Seroc onversion to SPf66 by enzyme-linked immunosorbent assay occurred in 76 % of volunteers receiving two or three doses. This vaccine was safe an d immunogenic in malaria-experienced Karen adults and children. This s tudy establishes the comparability of U.S.-manufactured SPf66 with tha t of Colombian origin, and is important for interpreting the efficacy results of U.S.-manufactured SPf66 in the same study population.