2015–2016 Zika virus epidemic

In early 2015, a widespread epidemic of Zika fever, caused by the Zika virus in Brazil, spread to other parts of South and North America. It also affected several islands in the Pacific, and Southeast Asia. In January 2016, the World Health Organization (WHO) said the virus was likely to spread throughout most of the Americas by the end of the year. In November 2016, WHO announced the end of the Zika epidemic.

In February 2016, WHO declared the outbreak a Public Health Emergency of International Concern as evidence grew that Zika can cause birth defects as well as neurological problems. The virus can be transmitted from an infected pregnant woman to her fetus, then can cause microcephaly and other severe brain anomalies in the infant. Zika infections in adults can result in Guillain–Barré syndrome. Prior to this outbreak, Zika was considered a mild infection, as most Zika virus infections are asymptomatic, making it difficult to determine precise estimates of the number of cases. In approximately one in five cases, Zika virus infections result in Zika fever, a minor illness that causes symptoms such as fever and a rash.

The virus is spread mainly by the Aedes aegypti mosquito, which is commonly found throughout the tropical and subtropical Americas. It can also be spread by the Aedes albopictus ("Asian tiger") mosquito, which is distributed as far north as the Great Lakes region in North America. People infected with Zika can transmit the virus to their sexual partners.

A number of countries were issued travel warnings, and the outbreak was expected to reduce tourism significantly. Several countries took the unusual step of advising their citizens to delay pregnancy until more was known about the virus and its impact on fetal development. Furthermore, the outbreak raised concerns regarding the safety of athletes and spectators at the 2016 Summer Olympics and Paralympics in Rio de Janeiro.