LONDON (AP) — The World Health Organization says Malawi has become the first country to begin immunizing children against malaria, using the only licensed vaccine to protect against the mosquito-spread disease.

Although the vaccine only protects about one third of children who are immunized, those who get the shots are likely to have less severe cases of malaria. The parasitic disease kills about 430,000 people every year, the majority of them children under 5 in Africa.

The vaccine, known as Mosquirix, was developed by GlaxoSmithKline. A previous trial showed the vaccine was about 30% effective in children who got four doses, but that protection waned over time.

WHO's Director-General Tedros Adhanom Ghebreyesus welcomed the new program, noting progress has "stalled and even reversed" in the ongoing fight against malaria.