Public health officials in São Paulo state are urging residents to check their vaccination records following a 2018 campaign that utilized a fractional dose of the yellow fever vaccine due to supply constraints. While research indicates this reduced dose provided sufficient immunity for up to eight years, boosters are now recommended for those vaccinated during that period. This guidance comes as Brazil continues to monitor for both yellow fever and measles, having recently regained measles-free status in 2024 after a previous loss in 2019-and amid ongoing outbreaks globally.
Individuals who received a fractional dose of the yellow fever vaccine in 2018 are advised to visit a local health center (UBS – Unidade Básica de Saúde) to complete the vaccination schedule, according to the São Paulo State Department of Health, following recommendations from the Ministry of Health.
This guidance comes after health authorities across Brazil implemented a fractional dose strategy in 2018 due to limited vaccine supplies amid a rise in yellow fever cases. “In 2018, we adopted the fractional strategy because there wasn’t enough vaccine for everyone,” explains Regiane de Paula, health coordinator at the CCD (Coordenadoria de Controle de Doenças) of the São Paulo State Health Department.
Research from the Oswaldo Cruz Foundation (Fiocruz) indicates that the fractional dose provides protection equivalent to the conventional dose for at least eight years, extending through this year. De Paula emphasizes that anyone unsure whether they need a booster should consult with their local UBS.
The São Paulo State Department of Health has confirmed 57 cases of yellow fever and 34 related deaths in the state as of 2025. This underscores the continued importance of vaccination efforts to prevent the spread of this potentially serious disease.
A current vaccination campaign, launched on January 12th, also focuses on reinforcing measles immunization. While Brazil regained its status as a measles-free country in 2024 – after losing it in 2019 – outbreaks continue to occur in other nations, such as the United States.
Last year, São Paulo state recorded two imported cases of the measles virus. “We reinforce the importance of complete measles vaccination, especially for those working in tourism, taxi drivers, and similar professions,” says the CCD coordinator, adding that the state’s major international airports and ports make it a potential entry point for the virus.
Who Should Get Vaccinated
For Yellow Fever:
- Individuals vaccinated with a fractional dose in 2018;
- Children: one dose is recommended at 9 months of age, with a booster at four years;
- People who received only one dose before age five should receive a booster dose;
- Individuals aged five to 59 who have not been vaccinated should receive a single dose.
For Measles:
- Children: first dose at 12 months of age (measles, mumps, and rubella – MMR vaccine) and a second dose at 15 months (MMR and varicella – MMRV vaccine);
- People aged five to 29 should receive two doses of the vaccine, with a minimum interval of 30 days between doses;
- People aged 30 to 59 should receive one dose of the vaccine;
- Healthcare workers should receive two doses of the MMR vaccine, depending on their vaccination status, regardless of age.
