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 the director of the Malaria Vaccine Initiative, which backed the latest study, Melinda Moree.