Brazil is currently in the seasonal period for yellow fever, which lasts from December to May. The expansion of the historical yellow fever transmission zone into areas in the southeastern part of the country in areas along the Atlantic coast, previously considered safe, has resulted in two waves of transmission (Figure 1). . One during the 2016-2017 seasonal season, with 778 human cases, including 262 deaths, and another during the seasonal period 2017-2018, with 1376 human cases, including 483 deaths.

From December 2018 to January 2019, 361 confirmed human cases, including eight deaths, were reported in 11 municipalities in two states of Brazil. In the southern part of the state of São Paulo, seven municipalities: El dorado (16 cases), Jacupiranga (1 case), Iporanga (7 cases), Cananeia (3 cases), Cajati (2), Pariquera-Açu (1 case) ) and Sete Barras (1) reported confirmed cases. In the same state, additional cases in the municipalities of Vargem (1) and Serra Negra (1) were confirmed at the border with the state of Minas Gerais. In addition, two cases were confirmed in the municipalities of Antonina and Adrianópolis, located in the eastern part of the State of Paraná. These are the first confirmed cases of yellow fever reported since 2015 from Paraná, a populous state with an international border. Of these confirmed cases, 89% (32/36) are men, the median age is 43 years and at least 64% (23/36) are rural workers.

Human cases reported so far during the current 2018-2019 period (July 2018 to January 2019) in nine municipalities in the state of São Paulo, as well as confirmation of human cases and epizootic Yellow fever in the state of Paraná mark the beginning of what could be a third wave and a progression of the epidemic to the southeastern and southern regions of the country (Figure 2). While it is too early to determine whether the high number of human cases observed during the last two seasonal highs is high, it appears that the virus continues to spread southward and in areas of low population immunity. .

Figure 1. Distribution of confirmed cases of human yellow fever by date of onset of symptoms in Brazil from 2016 to 2019.

Source: Data published by the Brazilian Ministry of Health (2016-2018, as of December 15, 2018) and the São Paulo State Health Secretariat (from December 22, 2018 to January 26, 2019) and reproduced by the Ministry of Health. Pan American Health Organization (PAHO / WHO). )

Figure 2. Distribution of epizootics and confirmed human cases in Brazil from January 1, 2016 to January 26, 2019.

Surveillance of non-human primate epizootics (HNP)

From 1 July 2018 to 18 January 2019, 25 confirmed epizootics were reported in five federal entities: São Paulo (13), Rio de Janeiro (8), Minas Gerais (1), Mato Grosso (2) and Parana (1). In the past four weeks, epizootics have been confirmed in the states of São Paulo and Parana. In addition, the Paraná Health Secretariat reported that tests on dead monkeys in Antonina, on the Paraná coast, were positive for yellow fever. Given the gradual geographical expansion of the epizootic wave that Brazil has experienced over the past two seasons, the country has had to adapt its vaccination policies against yellow fever. The number of areas for which vaccination is recommended has increased from 3526 municipalities in 2010 to 4469 (out of 55702) municipalities in 2018. In accordance with World Health Organization guidelines, Brazil has adopted a vaccination program in single dose against yellow fever since April 2017.

Public health response

During the 2017-2018 season, Brazil adopted the yellow fever split-dose vaccine to deal with epidemics and the risk of urbanization of yellow fever, especially in large cities. This strategy was implemented in 77 municipalities with the highest risk of yellow fever in the states of São Paulo (54 municipalities), Rio de Janeiro (15 municipalities) and Bahía (8 municipalities).

As of September 29, 2018, the preliminary results of the yellow fever mass vaccination campaign indicated that 13.3 million people in São Paulo, 6.5 million in Rio de Janeiro and 1.85 million in the states of Bahía were vaccinated, which represents a vaccination coverage of 53.6%, 55.6%. % and 55.0%, respectively3.

In addition, data from the Brazilian Ministry of Health indicate that vaccination coverage of 95% and above was achieved in 13% (57/435) of municipalities considered to be at risk in Paraná, 21% (113/531) of municipalities -risk in Rio Grande do Sul, 19% (155/838) municipalities at risk in São Paulo and 9% (38/428) municipalities at risk in Santa Catarina.

Brazil has recommended vaccinating an estimated 3 million additional people in the urban area of ​​Sao Paulo State in response to the current season, but has not yet determined the full or split dose. In January 2019, vaccinations also started in 36 communities in Quilombo – indigenous populations living in an environment at high risk of sylvatic transmission – in the Sao Paolo region and nearly 3,300 people were vaccinated in the municipality of Sao Paolo. Antonina, in the state of Paraná. In addition, the state and the affected municipalities have set up a task force that has targeted the vaccination of an additional 28,299 unvaccinated people over the next few days in the municipalities of Cajati, Iporanga and Barra do Turvo.

WHO risk assessment

An additional transmission is expected in the coming months depending on seasonal trends. Recent human cases of yellow fever during the current seasonal cycle have been reported in the states of São Paulo and Paraná in southeastern Brazil.

Preliminary results of immunization coverage in the municipalities of Paraná, Rio Grande do Sul, São Paulo and Santa Catarina States suggest a high proportion of people at risk and the need to intensify communication between the groups at risk. high risk.

The geographical distribution of human cases and epizootics of the two current and previous seasonal cycles suggests a southward movement of the virus, posing an additional risk for the states of Paraná, Rio Grande do Sul and Santa Catarina, no epizootic or case humans have been confirmed. in the last years before. In addition, these areas have favorable ecosystems for the transmission of yellow fever and borders with other countries such as Argentina, Paraguay and Uruguay.

During the previous season's cycle, cases of human yellow fever have been reported among travelers, although to date, most imported cases have been reported in countries where the vector is absent (or absent). in winter). These reports illustrate the importance of maintaining high levels of awareness, particularly for international travelers from areas where ecosystems are conducive to yellow fever transmission.

To date, the transmission of yellow fever by Aedes aegypti has not yet been documented. However, the high incidence observed during the last two seasons may reflect increased contact with sylvatic environments (vectors and non-human primates) and under-protected populations in urban or peri-urban areas. Urban. The sylvatic yellow fever virus is transmitted to monkeys by mosquitoes living in the forest, such as Haemagogus and Sabethes spp. Humans exposed to these mosquitoes can become infected if they are not vaccinated. Entomological studies conducted during the 2016-2017 epidemic in some of the affected states have shown that isolated Haemagogus mosquitoes were yellow fever positive, indicating predominantly sylvatic transmission. More recently, a survey conducted by the Evandro Chagas Institute and reported by the Brazilian Ministry of Health revealed the detection of yellow fever virus in Aedes albopictus mosquitoes caught in rural areas of two municipalities of Minas Gerais. (Itueta and Alvarenga) in 2017. this finding requires further investigation. The last documented yellow fever outbreak in urban Brazil was recorded in 1942.

WHO continues to monitor the epidemiological situation and reviews the risk assessment based on the latest available information. At present, based on the available information, WHO estimates that the overall risk is high at the national level, moderate at the regional level and low at the global level.

Council of the WHO

On January 25, 2019, PAHO / WHO alerted 4 Member States about the start of the seasonal yellow fever period and, therefore, the highest risk of transmission to unvaccinated humans. Thus, PAHO / WHO advises Member States with areas at risk of yellow fever to continue their efforts to vaccinate at-risk populations and to take the necessary steps to keep travelers informed and vaccinated before traveling to the affected areas. areas where vaccination against yellow fever is recommended.

WHO recommends vaccination of international travelers over nine months of age traveling to Brazil. On May 3, 20185, WHO updated the updated areas at risk of yellow fever transmission and the corresponding recommendations for vaccination of international travelers. the map of revised recommendations for yellow fever vaccination and risk areas is available on the WHO International Travel and Health website.

Vaccination against yellow fever can be easily prevented, provided vaccination is given at least 10 days before travel. Vaccination against yellow fever is safe, highly effective and provides lifelong protection. In accordance with the IHR (2005), the validity of the International Certificate of Vaccination against Yellow Fever extends to the life of the vaccinated person. A booster dose of yellow fever vaccine may not be required from international travelers as a condition of entry.

Sensitivity to the signs and symptoms of yellow fever is recommended for anyone living or traveling in areas at risk of yellow fever transmission. People with symptoms are encouraged to seek treatment quickly.

WHO recommends that no general restrictions on travel or trade in Brazil be based on information available for this event.

Resources

Information on the yellow fever situation in Brazil and in other countries of the Americas is published regularly on the PAHO / WHO website:

Information on the yellow fever situation in Brazil is available on the website of the Brazilian Ministry of Health:

For more information on yellow fever, please see:


1The likely place of infection of a confirmed human case is currently the subject of an investigation.

2Brazilian Institute of Geography and Statistics (IBGE, by its acronym in Spanish)

3It should be noted that these figures include 11.3 million people vaccinated in the three states before the launch of the mass vaccination campaign, which began on 25 January 2018 in São Paulo and Rio de Janeiro and 19 February 2018 Bahía.