LONDON — 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 last year done in slightly older children, which suggested the vaccine cut the malaria risk by about half — though that is still far below the protection provided from most vaccines. According to details released on Friday, the three-shot regimen reduced malaria cases by about 30 percent in infants aged 6 to 12 weeks, the target age for immunization.
Dr. Jennifer Cohn, a medical coordinator at Doctors Without Borders, described the vaccine’s protection levels as ‘‘unacceptably low.’’ She was not linked to 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, there are several dozen malaria vaccine candidates being researched.
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 last 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 babies who got three doses of the vaccine had about 30 percent fewer cases of malaria than those who didn’t get immunized. The research included more than 6,500 infants in Africa. Experts also found the vaccine reduced the amount of severe malaria by about 26 percent, 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.