Risk assessment: Wild-type poliovirus 1 transmission in Israel – what is the risk to Europe?
The EU/EEA countries and the rest of the WHO European Region, have been officially polio-free since 2002. However, wild-type polio virus 1 (WPV1) has been isolated in sewage and in the faeces of asymptomatic carriers in Israel since February 2013. In this risk assessment ECDC looks at the potential impact of this public health event on the risk of poliovirus being imported and re-established into circulation in EU/EEA.
The assessment evaluates three populations for the risk of infection with WPV (asymptomatic infection and shedding of virus) and the risk of clinical disease (paralytic poliomyelitis) in the EU: cohorts vaccinated with OPV; cohorts vaccinated exclusively with IPV-containing vaccines and population groups with low vaccination coverage, including people for whom the vaccine has failed or who have waning immunity.
Based on the evidence available, the overall threat posed by poliovirus re-establishment can be considered to be very low in OPV vaccinees for both poliovirus infection and disease; moderate in IPV-only cohorts for poliovirus infection and low for disease; and high in low or unvaccinated groups for poliovirus infection and moderate for disease.
The recent detection of wild-type polio virus 1 (WPV1) in sewage and asymptomatic carriers in Israel raises new questions on the potential for the importation and re-establishment of WPV in EU/EEA countries. In the new rapid risk assessment, ECDC concludes that there is the possibility that poliovirus may be imported and re-established in the EU/EEA. Furthermore, based on the limited information on existing surveillance systems, there is a risk that poliovirus circulation will go undetected if it is imported.
The highest level of risk is posed by the proximity of clustered un- or under-immunised population groups to large populations vaccinated using inactivated polio vaccine (IPV)-only schemes. Sub-optimal hygiene and crowded living conditions may also play a role in facilitating the spread of infection.
Vaccination coverage levels in the EU/EEA can be considered satisfactory as a whole (>90% for three doses of either IPV or OPV) and can explain the absence of WPV circulation in the region so far.
However, there are also pockets of the population that are un- or under-immunised who are at greater risk of infection and disease.
It is estimated that 12 million people in the EU under the age of 29 have not been vaccinated or completed the recommended national primary vaccination schedule for polio.
Unvaccinated pockets need to be identified, and targeted actions to increase vaccination coverage in these populations need to be addressed urgently.
“If WPV can re-emerge in Israel, with a comparable healthcare system to much of the EU and polio vaccination coverage, then we must accept that there is risk that it could re-emerge in the EU/EEA.
The way to prevent this is not easy but it is known: prevent; detect; respond. Additional efforts have to be made to have at least a national average of 90% vaccination coverage rate and un- and under vaccinated groups need to be identified and targeted.
Surveillance systems need to be in place and working well to detect poliovirus early. And finally, Member States need to have national response plans in place in the event of an outbreak.
This is exactly what the Israeli public health authorities have done to prevent the spread of poliovirus.” said ECDC Director, Dr Marc Sprenger.
Assessment of the risk
In the event of WPV being re-introduced the following conclusions can be taken:
- Those vaccinated with OPV are very unlikely to become infected and subsequently develop disease;
- There is a moderate risk that those with an IPV-only vaccine are infected with polio virus and a low risk that to develop disease;
- Individuals un- or under-vaccinated are at high risk of being infected with poliovirus and are at moderate risk to develop the disease
Humans are the only reservoir for polioviruses so travel between the EU/EEA and countries in which WPV circulates will largely determine the risk of the virus being imported into the EU/EEA. Europe has continuously been at risk since it was declared polio-free in 2002 given the significant population flow from and to the six countries(1) with reported polio outbreaks and Israel.
“For those countries without a national polio response plan in place, the WHO guidance and recommendations on this serve as an excellent basis.” said Dr Sprenger.
The latest surveillance data suggests there was no circulation of WPV or vaccine-derived poliovirus in the WHO European Region in 2012, confirming its polio-free status, as determined by the European Regional Certification Commission for Poliomyelitis Eradication (RCC). However surveillance systems need to be strengthened in EU Member States to allow timely poliovirus detection.
 Polio endemic countries are: Afghanistan, Nigeria and Pakistan; Ethiopia, Kenya and Somalia have all reported cases recently.