Brasilia, January 25, 2018 (PAHO) - Brazil today launched a mass immunization campaign that will deliver fractional doses of yellow fever vaccine to residents of 69 municipalities in the states of Rio de Janeiro and São Paulo. The strategic plan for the campaign was developed with support from the Pan American Health Organization (PAHO) and the World Health Organization (WHO). It will be the world's largest vaccination campaign, to date, using fractional doses of yellow fever vaccine.

Some 23.8 million people are expected to be vaccinated during the campaign, including 10.3 million in the state of São Paulo and 10 million in the state of Rio de Janeiro. The state of Bahia is expected to begin vaccinating on 19 February 2018 with an estimated target population of 3.3 million people to be reached with the vaccine.

Fractional dosing, also known as dose-sparing, is a way to extend vaccine supplies, protecting more people and reducing the possibility for disease spread. One-fifth of the regular dose of yellow fever vaccine still provides immunity against the disease for at least 12 months and likely longer. PAHO and WHO recommend the use of fractional doses of yellow fever vaccine in response to large-scale campaign needs. The use of fractional doses of yellow fever vaccine is not recommended as a longer-term strategy or to replace routine immunization practices.

Yellow fever vaccination

In this campaign, children aged, 9 months to 2 years, and people with medical conditions, among other groups, will receive the standard dose of the vaccine.

PAHO and WHO have provided wide-ranging support to the Brazilian government and to states in responding to yellow fever outbreaks since last year. This has included supplying yellow fever vaccine, purchasing syringes through the PAHO Revolving Fund, disseminating recommendations based on the best available scientific evidence, acquiring special vaccination cards for fractional doses (as was used in the Democratic Republic of the Congo), and working in the field alongside the national and local authorities.

In December 2017, at the request of Brazil's Ministry of Health, experts from PAHO, the Global Outbreak Alert and Response Network (GOARN) and WHO organized a workshop for yellow fever control specialists in Brasilia  on vaccination strategies-including dose fractioning-to be used in the event of outbreaks in large cities.

In 2017, PAHO mobilized more than 20 experts to the states of Bahia, Espírito Santo, Minas Gerais and Rio de Janeiro to assist with Aedes mosquito control to minimize the risk of urban outbreaks, perform detailed data analyses to support strategic actions, train national professionals, conduct epidemiological research on suspected and confirmed cases, and update health care guidelines and protocols.

This year, PAHO teams have traveled to Minas Gerais to assist with the identification of yellow fever epizootics (outbreaks in monkeys). This work will support the efforts of the national and state health authorities to better understand the circulation of yellow fever virus and as a consequence to plan focused vaccination strategies.

Experts from WHO and PAHO will also be in Rio de Janeiro and São Paulo to support and monitor the vaccination campaign and the associated surveillance activities.

Yellow Fever is an acute viral hemorrhagic disease transmitted by infected mosquitoes. It can be prevented by an effective, safe and affordable vaccine.  To date, all of the human cases of yellow fever in Brazil have been linked to  sylvatic mosquitoes.  The last case of urban yellow fever in Brazil occurred in 1942.

Case counts

According to Brazil's Ministry of Health, between July 1, 2017 and January 23, 2018, 130 cases of yellow fever were confirmed in the country, of which 53 resulted in death.

During the same period one year earlier, 381 confirmed cases and 127 deaths were reported. Yellow fever follows a seasonal pattern in Brazil, occurring mainly during the summer months.

Since 2017, Brazil's Ministry of Health has provided some 57.4 million doses of yellow fever vaccine to the states.

Routine vaccination

In Brazil, yellow fever vaccination is offered as part of routine immunization  in the following states: Acre, Amazonas, Amapá, Pará, Rondônia, Roraima, Tocantins, Federal District, Goiás, Mato Grosso do Sul, Mato Grosso, Bahia , Maranhão, Piauí, Minas Gerais, São Paulo, Rio de Janeiro, Espírito Santo, Paraná, Rio Grande do Sul and Santa Catarina.

Except for those with contraindications, health authorities advise that all persons living in these locations should receive the standard dose of yellow fever vaccine for life-long protection.