Malaria vaccine closer to reality

Firing new shots in the malaria war, a vaccine still in the testing stage is now a step closer to becoming a public health reality. Two new reports, from Kenya and Tanzania, show that the vaccine halves a child’s risk of getting malaria, setting the stage for an even larger trial that researchers hope will provide the definitive evidence needed for approval of what would be the first vaccine for the disease.

The new studies appear in the Dec. 11 New England Journal of Medicine.

“This is the only malaria vaccine to have reached this level of testing. It’s remarkable,” says William Collins, a malaria researcher at the Centers for Disease Control and Prevention in Atlanta. “I think this justifies the usefulness of moving on to the more large-scale trial.”

There are several types of malaria parasite, all spread among humans by mosquitoes. The vaccine, dubbed RTS,S by its maker GlaxoSmithKline targets the protozoan Plasmodium falciparum, which causes the most severe form of the disease.

For large-scale testing, researchers plan to start enrolling 12,000 to 16,000 children in several countries across Africa in 2009, says Ripley Ballou, an infectious disease physician at the Bill & Melinda Gates Foundation in Seattle. Babies vaccinated in that trial will be monitored for at least three years afterward, says Ballou, who coauthored both new reports.

In the Tanzanian trial, researchers started in 2006 to give 340 babies between 8 and 16 weeks of age a series of routine childhood immunizations. The researchers also randomly assigned half of the babies to receive three malaria vaccine shots and the others to instead get three hepatitis B vaccine shots, rather than just placebos. After each child’s last vaccination, the researchers monitored the baby’s health for nine months, on average.

During that time, eight of the babies vaccinated against malaria and 20 of those getting the hepatitis B vaccine developed malaria. After adjusting the data to account for other factors that might have skewed the results — such as use of mosquito nets over beds at night — the malaria vaccine still reduced disease risk by roughly half, says study coauthor Salim Abdulla, a physician and epidemiologist at the Ifakara Health Institute in Bagamoyo, Tanzania.

The study also shows that the malaria vaccine didn’t interfere with the effectiveness of other childhood vaccinations given simultaneously, Ballou says.

In the other trial, researchers in 2007 enlisted a slightly older group of babies, ranging from 5 to 17 months in age. Half of the 894 babies enrolled received the malaria vaccine that year while the other half got rabies vaccine shots during the same time period. Some of the children were in Kenya, some in neighboring Tanzania, says study coauthor Philip Bejon, a malaria researcher at the University of Oxford and the Kenyan Medical Research Institute in Kilifi.

During the eight months that followed the last shot for each child, 32 of those getting the malaria vaccine and 66 of those getting the rabies vaccine had developed malaria.

Unlike vaccines against smallpox or measles, the malaria vaccine provides only partial protection against disease. “We didn’t expect it to be 100 percent,” says Bejon. But, he adds, “this is very encouraging.” As with the other study, statistical adjustments to account for other factors — such as ages of the children, bed net use and even distance from a clinic — didn’t change the findings markedly.

If this malaria vaccine goes into production someday, the results could be striking, Abdulla says. Tanzania has roughly 18 million cases of malaria annually. “An intervention that would reduce this number by half would be very welcome,” he says.

It remains unknown how long the vaccine’s protection lasts. But Ballou notes that children who received the same vaccine in a trial in Mozambique several years ago still seem to have a degree of protection four years after immunization. The large trial set to start in 2009 will include some groups of children who will get malaria booster shots sometime after the normal regimen has concluded, he says.

Both newly released studies received funding or other resources from the Bill & Melinda Gates Foundation and GlaxoSmithKline.