Yellow fever activity in Brazil has occurred in areas near the Atlantic coast that were previously not considered to be at risk for disease transmission. As a result, the WHO and Brazilian Ministry of Health have issued new yellow fever vaccination recommendations for southern Bahia State, Espírito Santo State, and northern Rio de Janeiro State - all of which were areas previously not considered at risk for disease transmission. Additional areas along the Atlantic coast could be added to the list of places where the yellow fever vaccination is recommended in the coming weeks.
- The current yellow fever outbreak in Brazil appears to be a natural progression in the documented re-emergence of the virus in areas outside of the Amazon in recent years. Cases will likely be reported in other Brazilian states due to low vaccination rates and the movement of infected people and nonhuman primates in areas previously not considered at risk for disease transmission.
- There is currently no evidence that the yellow fever virus is being transmitted by Aedes mosquitoes, which are heavily populated in urban areas in Brazil. Circulation among the Aedes mosquito population could spark a larger and more urban outbreak.
- Additional areas along the Atlantic coast in eastern Brazil that were previously not considered at risk for yellow fever transmission could be added to the list of places where the yellow fever vaccination is recommended; therefore, it is vital to stay abreast of this evolving situation.
Yellow Fever Activity in Brazil
Brazil is experiencing a surge in yellow fever activity. As of Feb. 16, the Brazilian Ministry of Health reported more than 1,246 suspected human cases of yellow fever, 253 of which are confirmed, including 82 confirmed deaths, since December 2016; this compares to a total of 106 confirmed cases reported during the last major outbreak between 2007 and 2009. The large majority of the cases since December 2016 have occurred in the State of Minas Gerais, especially in the eastern part of the state. However, disease activity has also been confirmed in the neighboring states of Espírito Santo and São Paulo, while suspected cases have been identified in Bahia, Rio Grande do Norte, and Tocantins states (map). On Jan. 13, the governor of Minas Gerais State declared a state of emergency due to a yellow fever outbreak. In response to the ongoing outbreak, Brazilian authorities are conducting public education campaigns and increasing vector-control measures, disease surveillance, and vaccination coverage. Approximately 12.7 million vaccine doses have been distributed in affected states.
On Feb. 1, the US CDC issued an "Alert-Level 2" travel health advisory due to elevated yellow fever activity in the eastern Brazilian states of Bahia, Espírito Santo, Minas Gerais, Rio de Janeiro, and São Paulo, including areas where yellow fever vaccination had not been previously recommended. The US CDC's "Alert-Level 2" advisory is the second of three advisory levels, signifying elevated risk at a destination, often associated with specific risk factors. This level encourages travelers to take specific actions and emphasizes the need for enhanced health precautions - primarily obtaining a yellow fever vaccination and preventing mosquito bites, in the case of yellow fever. To be effective, the yellow fever vaccination must be administered at least 10 days prior to departure. In 2016, the WHO advised that yellow fever vaccination boosters were no longer recommended, and that a single dose, full-strength yellow fever vaccine is valid for life. While the US CDC also no longer recommends the booster, it does mention that a booster may be given to certain travelers. Specifically, this includes travelers who have received the vaccine more than 10 years ago and who will be in a high-risk location, like areas with ongoing outbreaks.
The current yellow fever outbreak appears to be a natural progression in the documented re-emergence of the virus in areas outside of the Amazon in recent years. Since 2014, authorities have detected increasing cases of yellow fever in nonhuman primates in southeastern states. The current yellow fever outbreak in Brazil is the result of the virus having been spread from nonhuman primates to humans by Haemagogus mosquitoes. Haemagogus mosquitoes are typically found in rural, forested areas of Brazil. The virus can also be spread by Aedes mosquitoes, which are heavily present in urban areas. If the disease begins to circulate in the Aedes mosquito population, a larger outbreak could be sparked. Yellow fever transmission in Brazil is typically the highest during the December-May rainy season, when environmental conditions are ideal for mosquito breeding. It is highly likely that cases will continue to be reported in the coming weeks as the season progresses. Furthermore, it is likely that cases will be reported in other Brazil states due to low vaccination rates and the movement of infected people and nonhuman primates in areas previously not considered at risk for disease transmission.
Yellow Fever Vaccination Recommendations
Prior to January 2017, yellow fever vaccination was not recommended for areas along the Atlantic coast in eastern Brazil. However, the recent surge in yellow fever activity in human and nonhuman primates in eastern Brazil has resulted in the WHO and Brazilian authorities designating multiple areas along the Atlantic coast at risk of yellow fever transmission, including southern Bahia State, Espírito Santo (with the exception of the urban area of Vitria) and northern Rio de Janeiro State. The WHO recommends that individuals traveling to these areas receive the yellow fever vaccine. The Brazilian Ministry of Health (MOH) and the WHO have both released a list of areas in the states of Bahia, Espírito Santo, and Rio de Janeiro where the yellow fever vaccination is now recommended (map). In addition to the recently added areas, yellow fever vaccination continues to be recommended for those traveling to most other Brazilian states, including Minas Gerais.
It is extremely important to stay abreast of the evolving yellow fever situation in Brazil, since the yellow fever vaccination could be recommended for areas previously not considered at risk for yellow fever transmission. For the most up-to-date information, contact the WorldAware Health Intelligence Department at firstname.lastname@example.org. It is also important to note that many countries require proof of yellow fever vaccination for travelers arriving from and/or transiting through a country with risk of yellow fever transmission, such as Brazil. For more information about countries requiring proof of yellow fever vaccination, click here.
Conclusion and Advice
Due to the evolving threat of yellow fever activity in areas near the Atlantic coast in eastern Brazil, the WHO and Brazilian MOH may recommend yellow fever vaccination in areas previously not considered at risk for disease transmission. Furthermore, vaccination recommendations for these areas could become permanent. Individuals traveling to or operating in Brazil should practice mosquito bite precautions and mosquito-breeding reduction efforts, such as removing standing water. Travelers should consult a travel medicine provider at least two weeks before departure to discuss yellow fever vaccination and any other health concerns. Yellow fever vaccination is recommended for individuals over the age of nine months in most Brazilian states. To be effective, the yellow fever vaccination must be administered at least 10 days prior to departure. A single dose, full-strength yellow fever vaccine is valid for life.