Phase I Trial of the SPf66 Malaria Vaccine in a Malaria-Experienced Population in Southeast Asia

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  • Shokio Malaria Research Unit, Hospital for Tropical Diseases, Mahidol University, Department of Immunology and Medicine, Armed Forces Research Institute of Medical Sciences, (AFRIMS), Department of Immunology, Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Medical Research, Nuffield Department of Clinical Medicine, John Radcliffe Hospital, Mae Sot, Thailand

In preparation for a recently reported, independent field trial of SPf66 malaria vaccine efficacy in Thailand, we first established the safety and immunogenicity of two clinical lots of U.S. manufactured lots of SPf66 in a series of overlapping Phase I studies. The vaccine was produced in approved laboratories using good manufacturing practices. Two clinical lots of alum-adsorbed SPf66 were evaluated in a combined, open-label, Phase I clinical trial involving 50 healthy, malaria-experienced Karen adults and children. Volunteers were grouped by age and immunized 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 SPf66 vaccine was well tolerated in this malaria-experienced population. The most common side effects were erythema, induration, warmth, and tenderness at the site of injection, which typically resolved within 24–48 hr. One adult volunteer developed an acute urticarial rash following the third dose. Among adults, and to a lesser extent older children, females had more local reactions than their male counterparts. Seroconversion to SPf66 by enzyme-linked immunosorbent assay occurred in 76% of volunteers receiving two or three doses. This vaccine was safe and immunogenic in malaria-experienced Karen adults and children. This study establishes the comparability of U.S.-manufactured SPf66 with that of Colombian origin, and is important for interpreting the efficacy results of U.S.-manufactured SPf66 in the same study population.