Detection of polio virus in sewage in England: analysis by Public Health France

The World Health Organization (WHO) on Wednesday 22 June confirmed the detection of poliovirus, derived from a type 2 vaccine strain, in wastewater samples taken as part of the surveillance. Located in London, this sewage treatment plant drains a population pool of 4 million people.

A vaccine-derived poliovirus (VDPV) is an attenuated strain of poliovirus that was originally included in the oral polio vaccine (OPV) and has evolved over time through genetic mutation to become virulent and behave more like a wild virus. As a result, it can be transmitted to people who are not properly vaccinated against poliomyelitis, causing the disease mainly in countries where the oral vaccine is used. Like the viruses contained in the oral vaccine, they are excreted in the stool of vaccinated people.

In France, as in many countries, vaccination against poliomyelitis is based on the use of the inactivated vaccine (IPV), which does not pose this risk.

Public Health France is monitoring the situation and also published the latest surveillance data on poliomyelitis in France and around the world in May.

What do we know about the English situation?

Between February and May 2022, several viruses with a virus profile derived from vaccinia poliovirus type 2 (VDPV2) were isolated from wastewater in London. Contrary to what is normally observed for poliovirus isolated from UK sewage (several evidence in recent years), these newer viruses appear to be genetically linked and suggest an episode of transmission within an undervaccinated community from a recently vaccinated individual from a country that does use the oral vaccine in its vaccination campaigns (the UK stopped using the oral vaccine in 2004). Viruses have only been detected in sewage samples, no cases of paralysis have been reported so far, and authorities believe the risk of spreading to the population is low, although there is a risk of transmission in underimmunized communities1. In the UK, immunization coverage for vaccines including polio for infants in London was estimated at 86.6%. English authorities have recalled the importance of checking and updating the vaccinations of London residents, particularly young children, regardless of their origin.

Cases of paralysis associated with a derivative of the poliovirus vaccine have been identified in Europe but are very rare

In addition, cases of paralysis caused by circulating vaccine-derived poliovirus (cVDPV) viruses were recently reported in Ukraine in October and December 2021 and Israel in February 2022, with corresponding isolates of cVPDV2 and cVPDV3. Regarding Ukraine, on April 28, 2022, the WHO reported 2 cases of cVPDV2-related paralysis and 19 contacts found positive in their environment, with the implementation of a vaccination campaign with IPV (inactivated polio vaccine) as a result was affected by the war in Ukraine in spring 2022.

A very low risk in adequately vaccinated populations

There is no treatment for poliomyelitis. The most important preventive measures relate to hygiene and vaccination, which have reduced the incidence of wild-type poliomyelitis worldwide by more than 99%.
France benefits from a very high poliomyelitis (inactivated polio vaccine) immunization coverage rate: 99% for primary vaccination and 96% for infant booster vaccinations in 2019, and these CV figures have historically been very high as vaccination has been mandatory up until now from the age of 12 until 2018. Babies born after 2018 are also required to be vaccinated.

This excellent coverage is reassuring and must be maintained and homogenized for all populations on the national territory. It offers very good protection against the disease in the event of contamination, so the risk of cases and/or clusters occurring within the French population remains very low.

Surveillance active in France to identify the poliovirus

Despite the elimination of poliomyelitis from the European area, great vigilance against the possible reintroduction of poliovirus is required. In fact, there are endemic herds associated with the wild virus worldwide (Pakistan and Afghanistan). The challenge, therefore, is to maintain high vaccination coverage until the disease is eradicated.

Public Health France, in collaboration with the national reference center for enteroviruses, has set up a poliomyelitis surveillance program based on the one hand on mandatory reporting (since 1936) and on the other hand on increased surveillance of enteroviruses since 2000. and based on a network of voluntary laboratories.

Since the establishment of the enterovirus surveillance network in 2000, only vaccine polioviruses and one type 2 cVDPV without recovery of virulence, all imported, with no evidence of infection capable of causing poliomyelitis, have been detected in clinical samples sampled from patients.

Health authorities in France remain vigilant about the risk of introducing vaccine-derived poliovirus strains linked to people from countries where the oral polio vaccine is still used. The clinical and biological surveillance coordinated by the CNR for enteroviruses and parechoviruses makes it possible to detect any clinical suspicion that requires rapid action to limit the risk of transmission. Catch-up vaccinations in unvaccinated or under-vaccinated populations are also important to prevent outbreaks of transmission from imported cases.

1 Polio: what do we know about the polioviruses discovered in the UK? BMJ 2022;377:o1578 – Emergency response to detection of vaccine-derived poliovirus type 2 (VDPV2) in London wastewater samples

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