U.S. researchers say the search for a malaria vaccine has gotten a boost thanks to some children living in Tanzania who have developed a natural immunity to the parasitic disease.

Those children develop an antibody capable of attacking the mosquito-born parasite, and an experimental malaria vaccine developed from those antibodies, injected into mice during five separate laboratory trials, was able to protect the animals from the often-fatal disease.

"I think there's fairly compelling evidence that this is a bona fide vaccine candidate," says researcher Jake Kurtis of the Center for International Health Research at Brown University School of Medicine, in Providence, R.I.

In a study reported in Science, the researchers describe taking blood samples at regular intervals from about a thousand children in the African nation during the early years of their lives and finding that a small portion of them, about 6 percent, had acquired a natural immunity to the disease, despite their living in a region with a high incidence of malaria.

Those immune children were producing an antibody capable of attacking the parasite at a vulnerable point of its life cycle, trapping it inside blood cells it has infected and keeping it from breaking out to spread the disease, the researchers found.

The experimental vaccine tests on the mice will be tried on laboratory monkeys in a few week, they said.

If those trials go well, human trials with a small group of volunteers could be attempted in around 18 months, they added.

However, despite the initial success of the vaccine, lots of work lies ahead because the parasite is "an incredibly difficult parasite to attack," Kurtis says. "It's had millions of years of evolution to co-opt and adapt to our immune responses -- it really is a formidable enemy."

Malaria, caused by a parasite that passes into the human body through a bite by an infected mosquito, kills some 600,000 people annually, with 90 percent of those deaths happening in sub-Saharan Africa, according to recent data from the World Health Organization.

Even those children who survive malaria face serious health problems later in life as a result of having had the disease, experts say.

A malaria vaccine is considered one of the "holy grails" of research into infectious diseases, particularly because of its deadly effect on children.

"This is the biggest, single-agent killer of children worldwide," Kurtis says.

Although animal trials don't always lead to similar success in humans, the researchers say in this case they are confident in the work because it began with human antibodies, thanks to those Tanzanian children.