Controlling malaria has long been a top goal of international public-health authorities. Caused by parasites transmitted by infected mosquitoes, malaria annually sickens more than 200 million people and kills nearly 800,000, mostly children in Africa. Because children are the most vulnerable to the disease, efforts to develop a vaccine have focused on them.
While far less protective than vaccines used against other diseases, the results of the test vaccine were hailed as a major advance.
“This is remarkable when you consider that there has never been a successful vaccine against a human parasite,” Tsiri Agbenyega of the Komfo-Anokye Hospital in Ghana, who is leading the study, told reporters during a briefing before the results were made public. “This potentially translates into tens of millions of cases of malaria in children being averted.”
Beyond causing disease and deaths, malaria saps many developing nations’ economies, accounting for 40 percent of medical costs, up to half of all hospitalizations and 60 percent of all visits to health clinics. Although it has largely been eliminated from most developed parts of the world, half of the world’s population live in areas where malaria remains endemic. It is the fifth leading cause of death from an infectious disease worldwide, the second leading cause of death in Africa and the leading cause of death in Africa among children younger than 5.
Bed nets treated with insecticide have reduced infections, but efforts to produce an effective malaria vaccine for children and adults have been repeatedly stymied. It is much more difficult to produce a vaccine against a parasite than against a virus, and the malaria parasite morphs its form at various stages in an infected person’s body.
Several experimental vaccines are being developed, but the one tested in the study is the most promising and by far the furthest along in development.
The vaccine’s developers hope to use the results of the study to win regulatory approval for the vaccine and make it available as soon as 2015. GlaxoSmithKline, which makes the vaccine, has pledged to sell it at an affordable price, charging just 5 percent above cost, and to work with suppliers to reduce the cost; to use any profit to develop a second-generation malaria vaccine; and to conduct research on other diseases that plague the developing world.
“Our intention is to supply this vaccine at the lowest cost possible,” said Glaxo’s chief executive, Andrew Witty. “We have no intention of making a profit here.”
Known by the technical name RTS,S, the vaccine was created more than 25 years ago by scientists at Glaxo and the Walter Reed Army Institute of Research by mixing part of the outer protein of the Plasmodium falciparum malaria parasite with a portion of a hepatitis B virus and a chemical that boosts the immune system’s response. Glaxo estimates that it has spent $300 million on the project, and about $200 million more has come from the Seattle-based Bill & Melinda Gates Foundation.
Researchers previously had reported preliminary results from smaller numbers of children in the study in Mozambique, Gabon, Ghana, Tanzania and Kenya, which provided tantalizing evidence that the vaccine was safe and at least partially effective.
The new report marks the first results from all 15,460 children ages 6 to 12 weeks and 5 to 17 months who received the vaccine or another one for comparison at 11 sites in Burkina Faso, Gabon, Ghana, Kenya, Malawi, Mozambique and Tanzania between March 2009 and January 2011.
A year after the first 6,000 children ages 5 to 17 months received all three doses of the vaccine, the shots reduced the risk of developing high fever and chills from infection with the parasite by 56 percent and the chances of developing a life-threatening case by 47 percent, the researchers reported. When they analyzed data about severe cases among all 15,460 infants and children, including those followed for up to nearly two years, they found that the vaccine was about 35 percent effective.
“This trial represents a powerful example of the high-quality science that is moving us toward controlling and someday even eradicating malaria,” said Christopher Elias, who heads PATH, a private nonprofit organization in Seattle that is organizing the vaccine effort. “We are on track to make history with this malaria vaccine trial.”
The findings were published online by the New England Journal of Medicine with an editorial to coincide with a presentation at a malaria forum in Seattle sponsored by the Gates Foundation.
The vaccine appears to be as safe as others, causing only relatively mild fevers and swelling at the injection site, the researchers said.
They plan to continue to track the children to see how long the protection lasts as well as gather more safety data on infants and how a booster dose affects the longer-term efficacy. Data from 32 months after the third dose should be available by the end of 2014.
Glaxo said it has no plans to try to develop the vaccine for use in adults.
Vasee Moorthy of the World Health Organization called the findings to date a “major scientific achievement.’’
“For the first time, we have confirmation of substantial efficacy against clinical malaria in a very large phase 3 trial of a malaria vaccine,” Moorthy said. “If licensed, this would be the very first human vaccine against a parasitic disease.”