BRASILIA (Reuters) - Public health officials in Brazil are working to stop an outbreak of yellow fever that has killed at least 40 people from becoming an epidemic and urged people in nine states on Thursday to seek vaccinations.

The Health Ministry said 70 cases of the fever and 40 deaths have been confirmed in the outbreak, centered in rural areas of the state of Minas Gerais, and another 47 deaths and 368 suspect cases are under investigation.

That is up from just seven cases last year and the highest number since 2003.

The call for people to get inoculated in nine out of Brazil’s 26 states caused public health centers to run out of vaccines as residents of those states rushed to get a shot.

The outbreak roughly covers an area of western Minas Gerais that was hit by Brazil’s worst environmental disaster last year when a tailings dam collapsed at the Samarco iron ore mine co-owned by BHP Billiton and Vale SA, polluting the Rio Doce river and heavily impacting the local ecosystem.

Health officials said at a news conference in Brasilia that there was no evidence linking the two events, but studies will be done to establish or rule out any connection to the disaster.

Yellow fever is a viral disease found in tropical regions of Africa and the Americas that mainly affects humans and monkeys and is transmitted by the same type of mosquito that spreads dengue and the Zika virus.

The outbreak comes as Brazil continues to battle Zika, which has led to a spike in babies being born with microcephaly, a condition marked by an abnormally small head and often resulting in grave developmental issues.

Most people recover from yellow fever after the first phase of infection, which usually involves fever, muscle and back pain, headache, shivers, loss of appetite and nausea or vomiting, according to the World Health Organization.

Health officials said they distributed 5.5 million yellow fever vaccines with another 11.5 million to follow in coming days and Brazilian biomedical research institution Fiocruz prepared to produce 9 million more.

In Brasilia, the capital, the death of one person suspected of picking up the virus in nearby Minas Gerais was being investigated, and inhabitants had to queue up for hours in some cases to get vaccinated.

Brazil has never managed to entirely eradicate rural yellow fever, but it has not registered cases of the disease in urban areas since 1942. It advises visitors from abroad to get vaccinated for yellow fever.