The Howlers’ Return

Between 2017 and 2018, a severe outbreak of sylvatic yellow fever in São Paulo killed thousands of primates, including about 2,500 brown howler monkeys (Alouatta guariba clamitans). Entire populations were wiped out in the Atlantic Forest, and in Cantareira State Park the species became functionally extinct.
To address this crisis, Brazilian researchers adapted the human yellow fever vaccine for safe use in wild primates. Led by CeMaCAS, with support from Fiocruz and the University of São Paulo, the team monitored rescued howler monkeys through clinical exams, serology, and behavioral studies. In February 2024, the first vaccinated individuals were reintroduced into the wild with GPS tracking, proving the protocol effective.
The project highlights how vaccinating wildlife can be a viable One Health strategy, protecting biodiversity while reducing the risk of emerging infectious diseases.