Insidious reintroduction of WPV1 in of wild poliovirus into Israel, 2013

Israel was certified as polio-free country in June 2002. The last case of polio was reported in 1988. Vaccination with Oral Polio Vaccine (OPV) was stopped in 2005, when Israel moved to an Inactivated Polio Vaccine (IPV) only schedule, with national vaccination coverage of 95%. Environmental surveillance, by systematic samples from sewage treatment facilities representing about 40% of the Israeli population was implemented since 1988.

In May 2013, wild-type polio virus 1 (WPV1) was isolated from routine sewage samples collected in April 2013 in two cities in the Southern district. Retrospective WPV1-specific analysis of samples indicated WPV1 introduction into that area in early February 2013.

Public health response included the following

A.   National Emergency response – National IPV catch up and IPV booster to the population in the epicenter of the event

B.   Intensified environmental surveillance (increased number of sites and frequency of sampling); as well of clinical monitoring (which included cases of acute flaccid paralysis and aseptic meningitis at all ages).

C.   Stool samples survey to characterized the distribution of WPV1 excretes in order to target the vaccination effort.

D.   Supplementary immunization activity (SIA) with bivalent OPV to children who were born since 2005.

Despite sustained WPV1 transmission virus identified by environmental surveillance, no clinical poliomyelitis cases were identified.

The main challenges of this event were the need for decision making in a unique situation – an "environmental outbreak" in an IPV-only vaccination country; and the complicated risk communication required for the re-introduction of OPV.

The event demonstrates possible introduction and sustained transmission of WPV in IPV-highly vaccinated population and the crucial role of environmental surveillance for early detection and monitoring of the intervention.