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Zika virus technical report: Interim Risk Assessment, WHO European Region, May 2016

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Executive summary

Background

On 1 February 2016, the WHO Director-General declared that recent clusters of cases of microcephaly and neurological disorders associated with Zika virus disease constitute a public health emergency of international concern under the International Health Regulations (2005). In light of the current widespread outbreak occurring in Latin America and the Caribbean, the risk for Zika virus importation and spread in the European Region should not be underestimated. To support countries in the European Region in targeting preparedness work and to guide prioritization of activities, the risk for a Zika virus disease outbreak was assessed.

Methods

The risk for an outbreak was considered to be the function of two main components: (1) the likelihood of local Zika virus transmission and (2) the capacity of countries to contain transmission at an early stage. A local transmission likelihood score was derived from the presence of and climatic suitability for Aedes aegypti and Ae. albopictus (the two species of Aedes mosquitos known to be competent vectors for Zika virus) and factors related to the introduction and onward transmission of Zika virus, such as a history of previous arboviral outbreaks, shipping and air connectivity, population density and urbanization. A country capacity score was derived by evaluating four main factors: integrated vector management, clinical surveillance, laboratory capacity and emergency risk communication.

Main limitations

After the declaration that microcephaly and neurological disorders associated with Zika virus represents a public health emergency of international concern, a rapid assessment of country capacity in relation to Zika virus was required. Therefore, the questionnaire used to collect data could not be pilot-tested, and the responses with regard to country capacity could not be validated. Thus, we cannot exclude the possibility that some questions might have been subject to interpretation and reporting biases. In addition, country capacity to respond to Zika virus has probably increased since the time of data collection; however, it was not possible to account for these changes in the analysis. The capacity score presented is therefore intended to serve as a baseline indicator at regional level. Countries are in the best position to assess their capacity in line with WHO recommendations according to their respective levels of likelihood of local Zika virus transmission.

In the absence of transmission models for Zika virus in the European Region (at the time of reporting), proxy indicators were used to derive the likelihood score for local transmission. The real probability that the pathogen will be disseminated once introduced is unknown. Comprehensive transmission models are required to estimate the probability of Zika virus transmission more accurately.

Results and conclusions

Many countries extending from the Mediterranean Basin are at moderate risk for local Zika virus transmission. In addition, three geographical areas (Madeira Island belonging to Portugal, and the Black Sea coastal areas of Georgia and the Russian Federation) with established populations of Ae. aegypti, were classified as having high likelihood for local Zika virus transmission. Although there was good overall capacity in the Region to contain Zika virus transmission at an early stage, capacity reported for specific activities (integrated vector management, surveillance, laboratory and emergency risk communication) varied substantially at country level. Reported capacity to prevent and rapidly control Zika virus transmission was fairly robust in countries with localized areas of high transmission likelihood.

Recommendations

Countries and regions at high or moderate likelihood of local Zika virus transmission should strengthen and/or maintain their vector control activities, with improved entomological surveillance and source reduction strategies. This will be particularly relevant in the three areas with Ae. aegypti before the active mosquito season starts, with enhanced clinical surveillance to rapidly detect local Zika virus transmission. Further, countries are advised to ensure that they have the laboratory capacity to test for Zika virus or have protocols in place to ship samples abroad for testing. Lastly, it is recommended that countries advise populations at risk on protecting themselves against infection and mitigating the effects of Zika virus infection and its complications.