A baby born in sub-Saharan Africa faces a lifetime of health risks, but none more challenging than surviving its first five years. A major reason for that is malaria, a parasitic disease spread by mosquitoes. Of the more than one million malaria deaths worldwide annually, roughly 90 percent are in children under five years of age and as many as 50 percent of the severe cases occur in babies under 18 months of age. But new results indicate that a vaccine previously shown to be safe and effective in adults and small children can also be safely administered to infants, potentially dramatically decreasing their risk of contracting the disease.
"In endemic areas, and particularly in the high-transmission areas of sub-Saharan Africa, children under one year of age carry a disproportionately high burden of disease," says physician Pedro Alonso, director of the Barcelona Center for International Health Research at the Hospital Clinic of the University of Barcelona, who led the new clinical trial. "You need to get to them and protect them as early as possible."
Researchers report in The Lancet that there were 62 percent fewer new cases of the disease among 214 infants between 10 and 18 months who had received the full three-dose course of the RTS,S/AS02A vaccine during this trial. And among all infants from a rural area in southern Mozambique who had received at least one injection, there were 35 percent fewer malaria episodes.
"As a father and a grandfather, and not just as a doctor and a policymaker, I tell you that this vaccine can make a profound difference in our lives," says physician Pascoal Mocumbi, a former Mozambican prime minister who also had served as health minister. This "will save lives."
The clinical trial is one of many being undertaken to assess the safety of the RTS,S vaccine developed by GlaxoSmithKline (GSK). Researchers say that it caused initial pain at the injection site (the thigh in babies) but that no other serious side effects were reported. A previous study showed the vaccine, created in 1987, reduced the malaria risk of young children between one and four years by 30 percent—an inoculation that lasted for at least 18 months. The vaccine also protected 34 percent of men in a study in Gambia.
RTS,S works by fusing a protein secreted by the malaria parasite with a molecule on the surface of hepatitis B virus that the human immune system recognizes and attacks. The researchers speculate that it works much like other vaccines, especially because the amount of protection conferred depends on the amount of malaria antibodies in the blood and malaria-recognizing, disease-fighting T cells in the liver. Neither on its own is sufficient, however, according to physician W. Ripley Ballou, vice president of global clinical research and development at GSK Biologicals. "There is something really important," he says, "in having both arms of the immune system working."
A large trial to determine the overall efficacy of the vaccine in children of all ages is expected to begin late next year, assuming results from ongoing safety trials continue to be positive. That trial will enroll at least 16,000 children from as many as 10 areas in seven African countries, Ballou says. It will investigate, among other things, whether adding a booster shot later in life provides added protection.
The good news is that the vaccine appears to be effective against all strains of the malaria parasite Plasmodium falciparum, and those initially protected have not shown any rebound effects later in life. "The vaccine does not seem to protect specifically against certain parasites," says molecular biologist Joe Cohen, vice president of research and development for emerging diseases, HIV and vaccines at GSK Biologicals. But "this is a question that we will need to continue to address in further studies and even probably after the vaccine has been implemented," which could come as soon as 2011 if all trials go well.