Malaria Vaccine Safe and Effective in Infants - Emma Hitt, PhD

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November 12, 2010 (Atlanta, Georgia) — The malaria vaccine candidate RTS,S/AS01E appears to be both safe and effective for treating malaria in infants, according to the findings of a phase 2 clinical trial conducted in sub-Saharan Africa.

Kwaku Poku Asante, MD, from the Kintampo Health Research Center in Ghana, reported the findings of an extended follow-up to a randomized controlled phase 2 infant trial here at the American Society of Tropical Medicine and Hygiene 59th Annual Meeting.

RTS,S/AS01E is a recombinant protein comprised of part of the circumsporozoite protein of the malaria parasite Plasmodium falciparum fused to the hepatitis B virus surface antigen. It is the first malaria vaccine to ever reach large-scale clinical testing.

"The RTS,S malaria vaccine is currently the only malaria vaccine that is being tested in the last phase of clinical trials prior to it being considered for approval for routine use," Dr. Asante told Medscape Medical News.

A number of previous studies have indicated that the vaccine is effective in preventing malaria infection in infants and young children. Dr. Asante and colleagues performed phase 2 clinical trials in 511 infants, aged 6 to 10 weeks, to assess the safety, immunogenicity, and efficacy of RTS,S/AS01E when coadministered with Expanded Program of Immunization vaccines for 19 months postimmunization.

Two immunization schedules — at 0, 1, and 2 months; and at 0, 1, and 7 months — were tested, and the 2 treatment groups were compared with a control group receiving the Expanded Program of Immunization vaccine alone.

Both schedules provided similar protection against malaria for 12 months after the third immunization, and were equally effective against both the first and multiple malaria episodes. However, the 0, 1, 2 month schedule was better at providing earlier protection. The efficacy against multiple malaria episodes during the entire treatment course (from 0 to 19 months) was 57.2% for the 0, 1, 2 month schedule, and 32.0% for the 0, 1, 7 month schedule.

In terms of immunogenicity, 94% of patients on the 0, 1, 2 month schedule and 85% of those on the 0, 1, 7 month schedule had detectable anticircumsporozoite antibodies, indicative of a response to immunization. The level of hepatitis B seroprotection was unaffected.

The 0, 1, 2 month schedule had the most reported serious adverse events (57 of 170, compared with 47 of 170 for the 0, 1, 7 month schedule; and 49 of 171 for the control group). However, serious adverse events did not appear to be vaccine-related, and no new safety concerns were raised.

David Poland, a spokesperson for the PATH Malaria Vaccine Initiative, which supported the trial, noted that smaller studies are already in progress to determine the efficacy of this vaccine in HIV-positive children and in combination with other common childhood vaccines, such as the pneumococcal and rotavirus vaccines.

The trial emphasizes the potential usefulness of the RTS,S/AS01E malaria candidate vaccine in treating infants and young children susceptible to malaria in sub-Saharan Africa, Mr. Poland told Medscape Medical News.

According to Dr. Asante, now that the vaccine has entered the final stage of clinical testing, if all goes according to plan, "general implementation of RTS,S/AS01E for infants 6 to 12 weeks of age will be possible within 5 years or so." The vaccine could also be available for older children (aged 5 to 17 months) as early as 2013.

The study was supported by GlaxoSmithKline Biologicals. The authors and commentator have disclosed no relevant financial relationships.

American Society of Tropical Medicine and Hygiene (ASTMH) 59th Annual Meeting: Abstract LB-2200. Presented November 5, 2010.