SAO PAULO (AP) — Brazil's Health Ministry says 424 people have been infected with yellow fever in the largest outbreak the country has seen in years. Of those, 137 have died.

An update published Thursday said that more than 900 other cases are under investigation. During the current outbreak in the Southern Hemisphere's summer rainy season, the vast majority of the confirmed cases have been in the southeastern state of Minas Gerais.

Much of Brazil is considered at risk for yellow fever, and people in those areas are supposed to be vaccinated. But this outbreak struck some areas not previously considered at risk, and Brazil is rushing vaccines to those areas.

Yellow fever is a mosquito-borne disease that cause causes fever, body aches, vomiting and can cause jaundice, from which it gets its name.