LONDON — Scientists have made important progress in the quest for a malaria vaccine, showing for the first time that childhood shots can prevent nearly one-third of cases and slash the risk of severe, life-threatening attacks by almost two-thirds.
Experts say the findings, outlined this week in The Lancet medical journal, provide robust evidence that the dream of developing a vaccine that will get babies through the most vulnerable period of infancy could become a reality by the end of the decade.
Researchers have been working on a malaria vaccine for more than 20 years, but until now none of the candidates showed promise. If this research bears fruit, it would be the first human vaccine against a parasite.
Specialists agree that, at least for the foreseeable future, there is no prospect of a vaccine that would wipe out malaria like the smallpox vaccine did for smallpox, or even provide lifelong immunity.
However, a vaccine that would turn the disease into a mostly mild infection would make a huge dent in the effort to control malaria, which kills a child every 30 seconds and poses a threat to half of all people on the planet. About 500 million episodes of malaria occur every year, mostly in the developing world. It is the leading killer of children under 5 in sub-Saharan Africa.
"We think a vaccine is important because as quick as you can make new drugs, there's resistance and (delivery of) bed nets has not been as simple as one would have hoped," said Melinda Moree, director of the Malaria Vaccine Initiative, which backed the latest study. "We've been trying to apply our existing technologies and the number of malaria deaths is rising. We need some new tools."
The vaccine, which GlaxoSmithKline Bio has been developing for 20 years, was tested in 2,022 children aged 1 to 4 in Mozambique, where the mosquito-borne disease is endemic.
After the children were treated with malaria drugs to get rid of any traces of the parasite, half got three shots of the malaria vaccine in three consecutive months, while the other half got other childhood vaccines.
The children were followed up for about six months and blood was taken every few weeks to check for malaria. Any new cases were immediately treated.
The researchers, led by Dr. Pedro Alonso at the University of Barcelona, found infection in 30 percent fewer children in the vaccine group than in the comparison group. The vaccine also reduced the risk of getting sick by 30 percent, the risk of getting repeated attacks by 30 percent, and cut by 58 percent the chance of developing severe malaria.
Within the comparison group, four children died of severe malaria, while none of the children who got the vaccine died of malaria.
The vaccine was most impressive in children under 2, in whom the disease is most dangerous. The vaccine reduced the number of severe malaria episodes in that age group by 77 percent.
Malaria is caused by the parasite Plasmodium falciparum, which is carried by mosquitoes. When the parasite is injected into the human body it is in a form that can only infect the liver, where it transforms and multiplies. After about a week, 10,000 daughter parasites leave the liver, now in a form that can infect red blood cells.
When one parasite invades a red blood cell, 10 pop out and in doing so, rip open the cell, killing it.
The vaccine, which targets the parasite before it invades red blood cells, is made using an antigen, a piece of a protein that sits on the surface of the parasite and can be recognized by the immune system. When the vaccine is injected, the immune system kicks into attack mode and makes antibodies.
When a mosquito later injects the parasite, the immune system recognizes it.
The antibodies stick to the surface of the parasite, hoping to stop it getting into the liver. If that doesn't work, the immune cells find the parasite in the liver and kill it there. And if that fails, scientists believe the immune cells reduce the multiplication of the parasite and block some of the more virulent daughters from getting out.
"Fewer parasites coming out of the liver and a possible filtering effect of preventing the virulent parasites from exiting, is one possible explanation for why we see less severe disease," said the vaccine's co-creator, Ripley Ballou of GSK Bio.
Further studies still have to be done to see that the vaccine works in children elsewhere in Africa and to verify that it will not interfere with other immunizations.
"It's quite obvious that there is going to be no single way of protecting against malaria. You won't do it just with drugs, you won't do it just with a vaccine or just with bed nets. You've really got to put these together," said Geoff Targett, a malaria researcher at the London School of Hygiene and Tropical Medicine who was not involved with the study.
"We may have to think about living with the parasite, but in a way where death and severe disease are very rare events. That's probably the way we'll end up," he said.