LAGOS, Nigeria (AP) — When a small number of cases of locally transmitted malaria were found in the United States last year, it was a reminder that climate change is reviving or migrating the threat of some diseases. But across the African continent malaria has never left, killing or sickening millions of people.

Take Funmilayo Kotun, a 66-year-old resident of Makoko, an informal neighborhood in Nigeria’s Lagos city. Its ponds of dirty water provide favorable breeding conditions for malaria-spreading mosquitoes. Kotun can’t afford insecticide-treated bed nets that cost between $7 and $21 each, much less antimalarial medications or treatment.

For World Malaria Day on Thursday, here is what you need to know about the situation in Africa:

MALARIA IS STILL WIDESPREAD

The malaria parasite mostly spreads to people via infected mosquitoes and can cause symptoms including fever, headaches and chills. It mostly affects children under 5 and pregnant women. Vaccine efforts are still in early stages: Cameroon this year became the first country to routinely give children a new malaria vaccine, which is only about 30% effective and doesn’t stop transmission. A second vaccine was recently approved.