Vaccine Halves Malaria Infections in Young Children

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Oct. 18, 2011 — An experimental vaccine cut malaria infections in infants and toddlers by about half, a new study shows.

“This is remarkable when you consider there has never been a successful vaccine against a human parasite nor obviously against malaria,” study researcher Tsiri Agbenyega, principal investigator of the study at Agogo Presbyterian Hospital in Agogo, Ghana, says in a news briefing.

The study is the largest test to date of the vaccine, called RTS,S, which has taken 20 years and more than $400 million to develop.

Final results of the trial aren’t expected until 2014, but if preliminary findings hold, experts say the vaccine will be a major advance against one of the world’s leading infectious disease killers.

“This is the first time anybody has been able to reach this point,” says Alberto Moreno, MD, an assistant professor of infectious disease at Emory University School of Medicine in Atlanta. Moreno has studied malaria for more than 35 years, but he was not involved in this study. “In the field, it will have a significant impact.”

The study is published in the New England Journal of Medicine.

Defeating Malaria

Malaria is caused by a parasite that’s most commonly passed to humans through the bite of an infected mosquito.

Although malaria has been eradicated in the U.S. since the 1950s, in other parts of the world it continues to be a major public health menace, causing more than 225 million infections each year and killing nearly 800,000 people. Most of those deaths occur in children in Africa.

So far, scientists have identified five different species of parasites that are responsible for causing malaria infectious. The new vaccine targets the deadliest.

Preventive efforts like bed nets, mosquito spraying, and medications to help control the infection “have made a tremendous dent in malaria, but despite that, over 700,000 children still die every year,” says researcher Mary J. Hamel, MD, a malaria epidemiologist at the CDC and a principle investigator on the RTS,S Malaria Vaccine Trial in Kenya. “So a vaccine like this, with 50% efficacy against severe disease, can have a very important role in controlling malaria and reducing the burden.”

For the study, researchers divided 6,000 African children who were 5 months to 17 months old into two groups. The first group got three doses of the malaria vaccine. The second group received three doses of rabies vaccine for comparison.

A year after both groups got their shots, researchers found that the malaria vaccine reduced the risk of developing malaria symptoms like fevers and chills by 56% and cut the risk of a severe and potentially deadly form of the disease by 47%.

“It’s a huge disease burden,” Hamel tells WebMD. “And these children, 75% were using insecticide-treated bed nets. You can imagine what it’s like for children who aren’t using bed nets.”

Serious adverse events, including seizures and meningitis, occurred in 18% of the experimental vaccine group and in 22% of the comparison group.

The study is being funded by GlaxoSmithKline and by the PATH Malaria Vaccine Initiative through a grant from the Bill and Melinda Gates Foundation.

Next Steps

By 2014, researchers say they will know more about how long protection from the vaccine lasts, how well it works in babies who are 6-12 weeks old, and whether or not children need a booster to maintain their protection.

“There are still important questions to be answered,” Hamel says. “If everything holds up, there’s the potential to save hundreds of thousands of lives.”

But because it only offers partial protection, researchers say it will need to be used in conjunction with other measures like mosquito nets, spraying, and medications.

“The future would be to make a second-generation vaccine that would be more efficacious, either building on this one, or there are other vaccines that are in early stages of development that are quite different. So one or the other,” Hamel says.

“I think if we end up with the first malaria vaccine, that will push everything forward because we will have shown that it can be done,” she says.

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