Yellow fever is a potentially deadly viral hemorrhagic disease transmitted by infected mosquitoes and its vaccine provides up to 99% lifetime immunity. The US Embassy and the Centers for Disease Control and prevention (CDC) issued a health alert for travellers visiting the cities of Rio de Janeiro, São Paulo and the Brazilian states of Espírito Santo and Bahia.
"Anyone 9 months or older who travels to or lives in these areas should be vaccinated against yellow fever," the CDC alert said.
Two of the largest mass vaccination campaigns against yellow fever ever seen in the world have begun in Nigeria and Brazil. Both campaigns, which are supported by the World Health Organization, aim to prevent the spread of the disease.
According to WHO the mass immunization campaign launched in Brazil has begun delivering fractional doses of yellow fever to nearly 24 million people in Rio de Janeiro and Sao Paulo. When there is a short supply of vaccines, fractional dosing (a short term effective strategy) can extend vaccine supplies to more people who can be protected from the spread of the disease.
A full dose of vaccine can provide life-long protection against yellow fever. One-fifth of the regular full dose can provide immunity against the disease for at least 12 months, maybe even longer.
WHO spokesman Tarik Jasarevic says the goal of the campaign is to reduce yellow fever transmission by achieving 90 percent coverage in those states.
"It is a part of an initiative to eliminate yellow fever epidemics," he said. "As you know, we cannot ... eradicate the yellow fever virus because it is being transmitted by mosquitoes. But, with the effective vaccine that exists for a number of years now, it can be prevented. So, mass vaccination is the best way to prevent outbreaks of yellow fever."