Zika virus: an epidemiological update - 14 April 2017

Overview

The 2015 outbreak of Zika fever in the Region of the Americas has demonstrated how a relatively obscure and mild mosquito-borne disease can become a global health emergency. In late 2015, WHO received reports from the Ministry of Health of Brazil of an unusual cluster of microcephaly and other neurological disorders potentially associated with Zika virus infections, along with retrospective reports from French Polynesia reporting similar findings that had occurred in 2013 and 2014. As a result, on 1 February 2016, WHO declared a Public Health Emergency of International Concern (PHEIC) following the advice of the Emergency Committee under the International Health Regulations (IHR) (Table 1).

Since its emergence in the Americas, Zika virus has been re-introduced to Africa, the region where it was first discovered, and to several Asian and Pacific region countries. From 1 January 2015 to 1 February 2017, 70 countries have reported Zika virus outbreaks or cases; of these, 59 reported Zika virus infections for the first time and 11 countries with a prior history of Zika virus transmission reported cases or outbreaks indicating possible endemicity. The actual number of infections by country is unknown due to patients not seeking medical care as symptoms are usually mild and many infections can be asymptomatic. Several countries, including Brazil and Colombia, reported large outbreaks, most likely due to the low level of pre-existing immunity to the virus and high population densities of competent vectors.