WHO and partners established a definition of what constitutes an outbreak, endemic transmission, and the interruption of mosquito-borne transmission in order to better characterize the level of transmission of Zika virus infection. This classification system was put into use as of the situation report of 7 July 2016.

In the 22nd June WHO report, 61 countries and territories have reported continuing mosquito-borne transmission of Zika virus. This number is made up of 47 countries who are experiencing a first outbreak of Zika virus since 2015, with no previous evidence of circulation, and with ongoing transmission by mosquitoes. 14 countries report evidence of Zika virus transmission between 2007 and 2014, with ongoing transmission. In addition, four countries or territories have reported evidence of Zika virus transmission between 2007 and 2014, without ongoing transmission: Cook Islands, French Polynesia, Isla de Pascua – Chile and Yap (Federated States of Micronesia).