Mem Inst Oswaldo Cruz, Rio de Janeiro, FAST TRACK

Yellow fever outbreak in Brazil: the puzzle of rapid viral spread and challenges for immunization

Cristina Possas1/+, Ricardo Lourenço de Oliveira2, Pedro Luiz Tauil3, Francisco de Paula Pinheiro1, Alcides Pissinatti4, Rivaldo Venâncio da Cunha5, Marcos Freire1, Reinaldo Menezes Martins1, Akira Homma1

1Oswaldo Cruz Foundation, Bio-Manguinhos, Rio de Janeiro, Brazil
2Oswaldo Cruz Foundation, Instituto Oswaldo Cruz, Rio de Janeiro, Brazil
3University of Brasilia, Medical School, Brasília, DF, Brazil
4Center of Primatology of Rio de Janeiro, State Environment Institute, Rio de Janeiro, Brazil
5Oswaldo Cruz Foundation, Campo Grande, Brazil

DOI: 10.1590/0074-02760180278
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We discuss the complex eco-social factors involved in the puzzle of the unexpected rapid viral spread in the ongoing Brazilian yellow fever outbreak, which has increased the reurbanization risk of a disease without urban cases in the Americas since 1942. Indeed, this rapid spatial viral dissemination to the Southeast and South regions, now circulating in the Atlantic Forest fragments close to peri-urban areas of the main Brazilian megalopolises (São Paulo and Rio de Janeiro) has led to an exponential increase in the number of yellow fever cases. In less than 18 months, 1,833 confirmed cases and 578 deaths were recorded most of them reported in the Southeast region (99,9%). Large epizooties in monkeys and other non-human primates (NHPs) were communicated in the country with 732 YFV laboratory confirmed events only in the 2017/2018 monitoring period We also discuss the peculiarities and similarities of the current outbreak when compared with previous great epidemics, examining several hypotheses to explain the recent unexpected acceleration of epizootic waves in the sylvatic cycle of the YFV together with the role of human, NHPs and mosquito mobility with respect to viral spread. We conclude that the most feasible hypothesis to explain this rapidity would be related to human behavior combined with ecological changes that promoted a significant increase in mosquito and NHP densities and their contacts with humans. We emphasize the urgent need for an adequate response to this outbreak such as extending immunization coverage to the whole Brazilian population and developing novel strategies for immunization of NHPs confined in selected reserve areas and zoos. Finally, we stress the urgent need to improve the quality of response in order to prevent future outbreaks and a catastrophic reurbanization of the disease in Brazil and other South American countries. Continuous monitoring of YFV receptivity and vulnerability conditions with effective control of the urban vector Aedes aegypti and significant investments in YF vaccine production capacity and research and development for reduction of adverse effects are of the highest priority.

key words: yellow fever vaccine

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