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Assessing the population at risk of Zika virus in Asia – is the emergency really over?
  1. Amir S Siraj,
  2. T Alex Perkins
  1. Department of Biological Sciences & Eck Institute for Global Health, University of Notre Dame, Notre Dame, Indiana, USA
  1. Correspondence to Dr Amir S Siraj; asiraj{at} and T Alex Perkins; taperkins{at}


On November 18, 2016, the WHO ended its designation of the Zika virus (ZIKV) epidemic as a Public Health Emergency of International Concern (PHEIC). At the same time, ZIKV transmission continues in Asia, with the number of Asian countries reporting Zika cases increasing over the last 2 years. Applying a method that combines epidemiological theory with data on epidemic size and drivers of transmission, we characterised the population at risk of ZIKV infection from Aedes aegypti mosquitoes in 15 countries in Asia. Projections made under the assumption of no pre-existing immunity suggest that up to 785 (range: 730–992) million people in Asia would be at risk of ZIKV infection under that scenario. Assuming that 20% of ZIKV infections are symptomatic, this implies an upper limit of 146–198 million for the population at risk of a clinical episode of Zika. Due to limited information about pre-existing immunity to ZIKV in the region, we were unable to make specific numerical projections under a more realistic assumption about pre-existing immunity. Even so, combining numerical projections under an assumption of no pre-existing immunity together with theoretical insights about the extent to which pre-existing immunity may lower epidemic size, our results suggest that the population at risk of ZIKV infection in Asia could be even larger than in the Americas. As a result, we conclude that the WHO’s removal of the PHEIC designation should not be interpreted as an indication that the threat posed by ZIKV has subsided.

  • epidemiology
  • medical entomology
  • public health
  • arboviruses
  • dengue

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  • Contributors ASS and TAP each contributed to all phases of the analysis and manuscript development.

  • Funding This research was supported by a RAPID award from the National Science Foundation (DEB 1641130) and by a grant from the National Institute of Allergy and Infectious Diseases at the National Institutes of Health (R01 AI102939-01A1).

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement Data and code used to generate the results in this manuscript are made available online at

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