The World Health Organization has approved a new vaccine for a strain of encephalitis that kills thousands of children and leaves many survivors with permanent brain damage.

The move allows United Nations agencies and other donors to buy it.

The disease, called Japanese encephalitis or brain fever, is caused by a mosquito-transmitted virus that can live in pigs, birds and humans. Less than 1 percent of those infected get seriously ill, but it kills up to 15,000 children a year and disables many more. Up to four billion people, from southern Russia to the Pacific islands, are at risk; it is more prevalent near rice paddies.

There is no cure.

The low-cost vaccine, approved last month, is the first authorized by the agency for children and the first Chinese-made vaccine it has approved.

It is made by China National Biotec Group and was tested by PATH, a nonprofit group in Seattle with funding from the Bill and Melinda Gates Foundation.