Brazil's Ministry of Health has ordered 11.5 million doses of yellow fever vaccines to reinforce its stockpiles amid the largest outbreak of the disease the country has seen since 2000, officials said.

So far during the summer rainy season, 70 cases, including 40 deaths, have been confirmed. More than 300 cases are still being investigated.

That makes it the biggest outbreak since 2000, when 85 cases were confirmed, according ministry data.

Around 5.5 million vaccine doses have already been sent to five states that have confirmed cases or are at risk, Eduardo Hage, director of the Department for Surveillance of Infectious Diseases, told a news conference.

The other 6 million ordered will arrive soon to join stockpiles. In addition, production of another 9 million doses has begun and should be available in the coming weeks.

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

Outbreaks are generally brought under control by vaccination campaigns.

Outbreak centred in southeastern state

Brazilian authorities recommend that the yellow fever vaccination be routine for anyone living in areas considered at risk. They are now advising anyone living in or travelling to areas with current outbreaks — or areas generally considered at risk — to get vaccinated, if they have not already. Brazil does not require a yellow fever vaccination for entry.

The current outbreak is centred in the southeastern state of Minas Gerais, which is within the at-risk area but didn't see any cases last year. There have also been a handful of confirmed cases in the neighbouring states of Sao Paulo and Espirito Santo, which has not had a case in decades.

"It's unusual," Jimmy Whitworth, professor of international public health at the London School of Hygiene & Tropical Medicine, said of the outbreak. "The more cases you have, the more chance that it's going to light up and take off in urban areas."

But he added that Brazilian authorities are taking the situation very seriously and appear to have enough vaccine stocks.

Officials at Wednesday's news conference said they are monitoring the disease closely to ensure it doesn't spread to urban areas, including ramping up vaccine stocks in Rio de Janeiro state, which has not had any cases but has a large population and is a popular beach destination is summer.

Though much of Brazil is considered at risk for yellow fever, it has seen only a handful of cases in each of the past few years. The last double-digit outbreak was in 2009, when 47 cases were registered.