The Brazilian state of Sao Paulo, the country’s most populous, is at risk of yellow fever, the World Health Organization (WHO) is warning.
The WHO is recommending that travellers to the state and its capital, Sao Paulo, get a yellow fever vaccine before visiting.
The warning comes after a significant rise in numbers of suspected and confirmed cases was reported.
Local officials say travellers will not be at risk if they stay in cities.
Brazilian Health Minister Antonio Nardi said the WHO advice stemmed from “an excess of concern”.
He said that while there had been an increase in the number of reported cases it did not constitute an “outbreak”.
He also said that most people attending Brazil’s famous carnival celebrations in February should be safe as they are held in large cities and not the rural and forested areas which have seen the biggest increase in yellow fever cases.
However, the WHO’s advice is for all travellers to the state to get a vaccination at least 10 days prior to travel and to take measures to avoid mosquito bites.
Brazilian health authorities said that since July 2017, 35 cases of yellow fever had been confirmed. Of those, 20 cases proved fatal. Sao Paulo has been the worst-affected state, with 20 confirmed cases.
Mr Nardi said Sao Paulo state authorities would speed up their vaccination campaign with the aim of vaccinating half of the state’s population by the end of February.
More than 45 million people live in the state of Sao Paulo.