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Phase-2 trials completed for children’s malaria vaccine
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Recently published results of two trials conducted to evaluate the safety, efficacy and immunogenicity of the investigational RTS,S/AS02D malaria vaccine with two different adjuvants were promising, indicating that the vaccine is a good candidate for inclusion in WHO’s Expanded Program on Immunization.
Results from a single-center, double blind, controlled trial involving 340 children aged younger than 12 months indicated that the RTS,S vaccine (GlaxoSmithKline) with the AS02D adjuvant did not interfere with immunologic responses to coadministered vaccines in the Expanded Program on Immunization. The vaccine and adjuvant also reduced the incidence of malaria and had a tolerable safety profile.
Patients were randomly assigned to receive three doses of either the RTS,S/AS02D vaccine or the hepatitis B vaccine when aged 8, 12 and 16 weeks, and both groups were concomitantly administered a combination of diphtheria and tetanus toxoids and whole-cell pertussis and conjugated Haemophilus influenzae type b vaccine (DTP with Hib).
Data indicated 98.6% of patients who received the vaccine had seropositive titers for anticircumsporozoite antibodies confirmed on enzyme-linked immunosorbent assay one month following vaccination. In the six-month follow-up period, the RTS,S/AS02D vaccine reduced first infection from Plasmodium falciparum malaria by 65.2% among these infants.
In a separate double blind, randomized trial involving 809 children aged 5 to 17 months, the researchers compared children who had episodes of clinical malaria and who received three doses of the RTS,S vaccine and the AS01E adjuvant with those children who received a control vaccine (three doses of human diploid cell rabies vaccine, Sanofi Pasteur).
Incidence of the first or only malarial episode among children receiving the RTS,S/AS01E vaccine was 8% (32 of 402) compared with 16% in the control group (66 of 407). The adjusted efficacy rate for RTS,S/AS01E was 53% (95% CI, 28 to 69; P<.001) using Cox regression. Greater than 99% of children receiving the RTS,S/AS01E vaccine had anticircumsporozoite titers, according to the researchers. Data indicated that the vaccine reduced clinical episodes of malaria by 53% during the eight-month follow-up period.
Separate phase-3 clinical trials are planned to evaluate both vaccine and adjuvant combinations.
N Engl J Med. 2008;doi:10.1056/NEJMoa0807773.
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Engl J Med. 2008;doi:10.1056/NEJMoa0807381.
There are few infectious diseases with the global importance of malaria. Certainly one of the most cost-effective means of controlling a widespread infectious disease in the developing world is implementation of an effective immunoprophylaxis program. Encouraging data from malaria vaccine trials brings us one step closer to the eventual prevention of millions of deaths from malaria that occur each year, particularly in children. Also, effective malaria immunoprophylaxis would make the world safer for international travelers venturing into malaria-endemic regions.
– Herbert L. Dupont, MD
St. Luke’s Episcopal Hospital, Houston