An experimental vaccine from GlaxoSmithKline halved the risk of African children getting malaria in a major clinical trial, making it likely to become the world’s first shot against the deadly disease.

Final-stage trial data released on Tuesday showed it gave protection against clinical and severe malaria in five- to 17-month-olds in Africa, where the mosquito-borne disease kills hundreds of thousands of children a year.

“These data bring us to the cusp of having the world’s first malaria vaccine,” said Andrew Witty, chief executive of the British drugmaker that developed the vaccine along with the non-profit PATH Malaria Vaccine Initiative (MVI).

While hailing an unprecedented achievement, Witty, malaria scientists and global health experts stressed that the vaccine - known as RTS,S or Mosquirix - was no quick fix for eradicating malaria. The new shot is less effective against the disease than other vaccines are against common infections such as polio and measles.

“We would have wished that we could wipe it out, but I think this is going to contribute to the control of malaria rather than wiping it out,” Tsiri Agbenyega, a principal investigator in the RTS,S trials in Ghana, told Reuters at a conference in Seattle about the disease.

Malaria is endemic in more than 100 countries worldwide and killed around 781,000 people in 2009, according to the World Health Organization.

Control measures such as insecticide-treated bednets, indoor spraying and the use of combination anti-malaria drugs have helped cut the numbers of malaria cases and deaths significantly in recent years, but experts say an effective vaccine is vital to complete the fight against the disease.

The new data, presented at the Bill & Melinda Gates Foundation’s Malaria Forum conference in Seattle and published simultaneously in the New England Journal of Medicine, were the first from a final-stage Phase III clinical trial conducted at 11 trial sites in seven countries across sub-Saharan Africa.

The trial is still going on, but researchers who analyzed data from the first 6,000 children found that after 12 months of follow-up, three doses of RTS,S reduced the risk of children experiencing clinical malaria and severe malaria by 56 percent and 47 percent, respectively.

“We are very happy with the results. We have never been closer to having a successful malaria vaccine,” said Christian Loucq, director of PATH MVI, who was at the Seattle conference.

Loucq added that widespread use of insecticide-treated bednets in the trial - by 75 percent of people taking part - showed that RTS,S can provide significant protection on top of other existing malaria control methods.

Results in babies aged six to 12 weeks are expected in a year’s time and, if all goes well, GSK believes the vaccine could reach the market in 2015.

Getting it to the African infants that need it will take a concerted effort from international funders, such as the Gates Foundation that helped pay for the research. Health experts say it must be cheap enough to be cost-effective.

Witty declined to say if a course of three shots would cost under $10 but told reporters RTS,S would be priced as low as possible. The company has previously said it will charge only the cost of manufacture plus a 5 percent mark-up, which will be reinvested into tropical disease research.

“We are not going to make any money from this project,” Witty said.

However, shares in GSK’s small U.S. biotech partner Agenus, which makes a component of the vaccine, jumped more than 40 percent on news of the positive clinical trial result.

PARASITE IN SALIVA

Malaria is caused by a parasite carried in the saliva of mosquitoes. The RTS,S vaccine is designed to kick in when the parasite enters the human bloodstream after a mosquito bite. By stimulating an immune response, it can prevent the parasite from maturing and multiplying in the liver.

Without that immune response, the parasite gets back into the bloodstream and infects red blood cells, leading to fever, body aches and in some cases death.

RTS,S’s co-inventor Joe Cohen said the data were robust and consistent with earlier trials, which also showed around 50 percent efficacy. Side effects, including fever and injection-site swelling, were similar in children given RTS,S and a control vaccine.

After working for 24 years on developing the shot, he said he was “very proud of what we have achieved”.

Some external commentators were cautious about the vaccine’s potential - health experts normally like to see a success rate of 80 percent plus in a vaccine - but said it was an important development that should save many lives.

“We’re probably not there yet, but this is a really important advance in science,” Peter Agre, director of the John Hopkins Malaria Research Institute and a former Nobel prize winner, told Reuters at the Seattle Malaria Forum.

In an editorial in the New England Journal of Medicine, Nicholas White of Thailand’s Mahidol University said, “It is becoming increasingly clear that we really do have the first effective vaccine against a parasitic disease in humans”.

###

By Kate Kelland and Ben Hirschler