Brazil's south-eastern state of Minas Gerais has declared a public health emergency following a deadly outbreak of yellow fever.
At least 15 people have died there since December. Many areas, including the state capital Belo Horizonte, have been affected.
A mass vaccination program is in place in three southern states.
But queues have formed outside clinics in Rio and Sao Paulo amid concerns that vaccines could run out.
In neighbouring Argentina, there have also been long queues for the vaccine in Buenos Aires and other cities as thousands of prospective tourists prepare to travel to Brazil for carnival.
On Tuesday the WHO recommended that travelers to Sao Paulo state get a yellow fever vaccine before visiting.
The health emergency will be in place for six months and will allow local authorities to commission special services and buy in emergency materials.
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