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The World Health Organization (WHO) confirmed on Wednesday, June 22, the detection of poliovirus derived from a type 2 vaccine strain, in wastewater samples taken as part of surveillance. This sewage treatment plant is located in London and drains a population 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 by 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 polio and cause the disease mainly in countries that use the oral vaccine. Like the viruses contained in the oral vaccine, they are excreted in the faeces of vaccinated persons.
In France, as in many countries, polio vaccination is based on the use of inactivated vaccine (IPV) which does not present this risk.
Public Health France is monitoring the situation and in May also released the latest surveillance data on polio in France and around the world.
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 sewage in London. Contrary to what is usually observed for polioviruses isolated from sewage in the UK (several detections in recent years), these recent viruses appear genetically linked and suggest an episode of transmission within an under-vaccinated community, from a recently vaccinated person from a country that uses the oral vaccine in its vaccination campaigns (the UK no longer uses the oral vaccine since 2004). The viruses have only been detected in wastewater samples, no cases of paralysis have been reported to date, and authorities consider the risk of spread to the population to be low, although there is a risk of transmission in underimmunized communities.1. In Britain, immunization coverage for vaccines, including polio for infants, was estimated at 86.6% in London. The English authorities have recalled the importance of checking and updating the vaccinations of people living in London, in particular of young children regardless of their origin.
Cases of paralysis linked to a poliovirus vaccine derivative already identified in Europe but very rare
In addition, cases of paralysis caused by circulating vaccine-derived polioviruses (cVDPV) were recently reported in Ukraine in October and December 2021 and Israel in February 2022, with respective isolates of cVPDV2 and cVPDV3. Regarding Ukraine, the WHO reported, on April 28, 2022, 2 cases of paralysis linked to cVPDV2, and 19 contacts found positive in their environment with the implementation of an IPV (inactivated polio vaccine) vaccination campaign in Ukraine. later period, campaign heavily impacted by the war in Ukraine in the spring of 2022.
A very low risk in sufficiently vaccinated populations
There is no treatment for polio. The main preventive measures are related to hygiene and vaccination, which have reduced the incidence of poliomyelitis due to the wild virus by more than 99% worldwide.
France benefits from very high vaccination coverage against polio (inactivated polio vaccine): 99% for primary vaccination and 96% for booster vaccination in infants in 2019, and these CV figures have always been very high, having been mandatory the vaccine up to the age of 12 until 2018. In addition, vaccination is mandatory for babies born from 2018.
This excellent coverage is reassuring and needs to be maintained and homogeneous for all the populations of the national territory. It provides very good protection against the disease in the event of contamination, so the risk of cases and/or clusters appearing in the French population remains very low.
In France, active surveillance to identify the presence of the polio virus
Despite the elimination of polio from the European region, great vigilance against a possible reintroduction of poliovirus is necessary. In fact, endemic foci linked to the wild virus persist in the world (Pakistan and Afghanistan). Therefore, the challenge is to maintain high vaccination coverage until the disease has been eradicated.
Public Health France has launched a polio surveillance program based on the one hand on compulsory notification (in force since 1936) and on the other hand on enhanced surveillance of enteroviruses since 2000, in collaboration with the National Reference Center for Enteroviruses, and based on a network of voluntary laboratories.
Since the establishment of the enterovirus surveillance network in 2000, in clinical samples, without any signs of infection, only vaccine poliovirus has been detected, as well as a type 2 cVDPV, without recovery of virulence, all imported, which could cause poliomyelitis in the sampled patients.
Health authorities in France remain vigilant of the risk of introduction of vaccine-derived poliovirus strains linked to people from countries where oral polio vaccine is still in use. The clinical and biological surveillance coordinated by the Enterovirus and Parechovirus CNR allows detecting any clinical suspicion that requires rapid action aimed at limiting the risk of transmission. Catch-up vaccination in unvaccinated or undervaccinated population groups is also important to prevent outbreaks of transmission of imported cases.
1 Polio: What do we know about polioviruses detected in the UK? BMJ 2022;377:o1578 – Immediate actions in response to detection of vaccine-derived poliovirus type 2 (VDPV2) in London sewage samples