title: Potential for international spread of wild poliovirus via travelers.
abstract: BACKGROUND
  The endgame of polio eradication is hampered by the international spread of poliovirus via travelers. In response to ongoing importations of poliovirus into polio-free countries, on 5 May 2014, WHO's Director-General declared the international spread of wild poliovirus a public health emergency of international concern. Our objective was to develop a mathematical model to estimate the international spread of polio infections.
  
  
  METHODS
  Our model took into account polio endemicity in polio-infected countries, population size, polio immunization coverage rates, infectious period, the asymptomatic-to-symptomatic ratio, and also the probability of a traveler being infectious at the time of travel. We applied our model to three scenarios: (1) number of exportations of both symptomatic and asymptomatic polio infections out of currently polio-infected countries, (2) the risk of spread of poliovirus to Saudi Arabia via Hajj pilgrims, and (3) the importation risk of poliovirus into India.
  
  
  RESULTS
  Our model estimated 665 polio exportations (>99 % of which were asymptomatic) from nine polio-infected countries in 2014, of which 78.3 % originated from Pakistan. Our model also estimated 21 importations of poliovirus into Saudi Arabia via Hajj pilgrims and 20 poliovirus infections imported to India in the same year.
  
  
  CONCLUSIONS
  The extent of importations of asymptomatic and symptomatic polio infections is substantial. For countries that are vulnerable to polio outbreaks due to poor national polio immunization coverage rates, our newly developed model may help guide policy-makers to decide whether imposing an entry requirement in terms of proof of vaccination against polio would be justified.
authors.affiliation: Lee Kong Chian School of Medicine, Nanyang Technological University, Mandalay Road 11, Singapore, 308232, Singapore. anneliesws@gmail.com.|Institute of Public Health, University of Heidelberg, Heidelberg, Germany. anneliesws@gmail.com.
authors.forename: Annelies
authors.initials: A
authors.lastname: Wilder-Smith
authors.affiliation: Lee Kong Chian School of Medicine, Nanyang Technological University, Mandalay Road 11, Singapore, 308232, Singapore. LeongWeiYee@ntu.edu.sg.
authors.forename: Wei-Yee
authors.initials: WY
authors.lastname: Leong
authors.affiliation: Florida International University, Miami, USA. llopez@fiu.edu.|School of Medicine, University of São Paulo, São Paulo, Brazil. llopez@fiu.edu.
authors.forename: Luis Fernandez
authors.initials: LF
authors.lastname: Lopez
authors.affiliation: Faculty of Veterinary Medicine, University of São Paulo, São Paulo, Brazil. amaku@usp.br.
authors.forename: Marcos
authors.initials: M
authors.lastname: Amaku
authors.affiliation: Department of Public Health and Clinical Medicine, Epidemiology and Global Health, Umeå University, Umeå, Sweden. mikkel.quam@gmail.com.
authors.forename: Mikkel
authors.initials: M
authors.lastname: Quam
authors.affiliation: Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada. Khank@smh.ca.|Faculty of Medicine, Division of Infectious Diseases, University of Toronto, Toronto, ON, Canada. Khank@smh.ca.
authors.forename: Kamran
authors.initials: K
authors.lastname: Khan
authors.affiliation: School of Medicine, University of São Paulo, São Paulo, Brazil. edmassad@usp.br.|London School of Hygiene and Tropical Medicine, London, UK. edmassad@usp.br.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Massad
mesh_terms: D003141:Communicable Diseases / Q000453:epidemiology* / Q000635:transmission; D004196:Disease Outbreaks / Q000517:prevention & control*; D006801:Humans; D007194:India / Q000453:epidemiology; D008962:Models, Theoretical; D011051:Poliomyelitis / Q000453:epidemiology* / Q000635:transmission; D017955:Poliovirus; D012529:Saudi Arabia; D014195:Travel