Brazil’s south-eastern state of Minas Gerais declared a public health emergency on Saturday following an outbreak of yellow fever in nearly 100 cities over the last several months, AP reported. Yellow fever is a disease caused by a virus that is transmitted to humans by mosquitoes.

The decree allows the government to hire health workers without a bidding process, and buy emergency materials. The emergency will be in place for six months.

At least 15 people have died of yellow fever in the state since December, according to the BBC. Since July 2017, 35 cases have been confirmed in Brazil and 20 have died, health ministry data showed.

In Minas Gerais alone, 475 cases were confirmed between January and June 2017, and 162 people died.

A mass vaccination programme is under way in three southern states of the country. The World Health Organization has said that the Sao Paulo state is also at risk and has advised travellers to get vaccinated. Minas Gerais is the hardest hit state.