An experimental malaria vaccine once thought promising is turning out to be a disappointment, with a new study showing it is only about 30 percent effective at protecting infants from the killer disease.
That is a significant drop from a study done last year in slightly older children, which suggested the vaccine cut the malaria risk by about half — and even that is far below the protection provided by most vaccines. The three-shot regimen reduced malaria cases by about 30 percent in infants aged 6 to 12 weeks, the target age for immunization, researchers reported Friday.
“We're all a bit frustrated that it has proven so hard to make a malaria vaccine," said Eleanor Riley of the London School of Hygiene and Tropical Medicine. She said a malaria vaccine might be useful if combined with other strategies, like bed nets.
"The question is how much money are the funders willing to keep throwing at it,” said Riley, who was involved in an earlier study of the vaccine and had hoped for better results.
Dr. Jennifer Cohn, a medical coordinator at Doctors Without Borders, described the vaccine's protection levels as "unacceptably low." She was not involved in the study.
Scientists have been working for decades to develop a malaria vaccine, a complicated endeavor since the disease is caused by five different species of parasites. There has never been an effective vaccine against a parasite. Worldwide, scientists are working on several dozen malaria vaccine candidates.
In 2006, a group of experts led by the World Health Organization said a malaria vaccine should cut the risk of severe disease and death by at least half and should protect for longer than one year. Malaria is spread by mosquitoes and kills more than 650,000 people every year, mostly young children and pregnant women in Africa. Without a vaccine, officials have focused on distributing insecticide-treated bed nets, spraying homes with pesticides and ensuring access to good medicines.
In the new study, scientists found 30 percent fewer cases of malaria among babies who got three doses of the vaccine compared to those who didn't get immunized. The research included more than 6,500 infants in Africa. Experts also found the vaccine reduced the number of cases of severe malaria by about 26 percent for up to 14 months after the babies were immunized.
Scientists said they needed to analyze the data further to understand why the vaccine may be working differently in different regions. For example, babies born in areas with high levels of malaria might inherit some antibodies from their mothers that could interfere with the vaccine.
"Maybe we should be thinking of a first-generation vaccine that is targeted only for certain children," said Dr. Salim Abdulla of the Ifakara Health Institute in Tanzania, one of the study investigators.
Results were presented at a conference in South Africa on Friday and released online by the New England Journal of Medicine. The study is scheduled to continue until 2014 and is being paid for by GlaxoSmithKline and the PATH Malaria Vaccine Initiative.
"The results look bad now, but they will probably be worse later," said Adrian Hill of Oxford University, who is developing a competing malaria vaccine. He noted the study showed the Glaxo vaccine lost its potency after several months. Hill said the vaccine might be a hard sell, compared to other vaccines like those for meningitis and pneumococcal disease — which are both effective and cheap.
"If it turns out to have a clear 30 percent efficacy, it is probably not worth it to implement this in Africa on a large scale," said Genton Blaise, a malaria expert at the Swiss Tropical and Public Health Institute in Basel, who also sits on a WHO advisory board.
Glaxo started developing the vaccine in 1987 and has invested $300 million in it so far.
WHO said it couldn't comment on the incomplete results and would wait until the trial was finished before drawing any conclusions.