The World Health Organization (WHO) confirmed Wednesday, June 22 the detection of polioviruses derived from a type 2 vaccine strain, in samples of wastewater taken as part of surveillance. This wastewater treatment plant is located in London and 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 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 poliomyelitis and cause the disease mainly in countries using the oral vaccine. Like the viruses contained in the oral vaccine, they are excreted in the stools of vaccinated individuals.
In France, as in many countries, vaccination against poliomyelitis is based on the use of the inactivated vaccine (IPV) which does not present this risk.
Public Health France is monitoring the situation and in May also published the latest surveillance data concerning poliomyelitis 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 United Kingdom (several detections in recent years), these recent viruses appear genetically linked and suggest an episode of transmission within an insufficiently vaccinated community, from a recently vaccinated person from a country using the oral vaccine in its vaccination campaigns (the United Kingdom no longer using the oral vaccine since 2004). Viruses have only been detected in sewage 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 under-immunized communities1. 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 residing in London, in particular young children regardless of their origin.
Cases of paralysis linked to a derivative of the vaccine poliovirus already identified in Europe but 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 respective isolations 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 entourage with the implementation of a vaccination campaign by IPV (polio vaccine inactivated) in the aftermath, 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 poliomyelitis. The main preventive measures relate to hygiene and vaccination, which has reduced the incidence of poliomyelitis due to the wild virus by more than 99% worldwide.
France benefits from a very high vaccination coverage against poliomyelitis (inactivated polio vaccine): 99% for the primary vaccination and 96% for the booster vaccination in infants in 2019, and these CV figures are very raised since always, the vaccine having been compulsory until the age of 12 until 2018. In addition, vaccination is compulsory for infants born from 2018.
This excellent coverage is reassuring and needs to be maintained and homogeneous for all populations on the national territory. It provides very good protection against the disease in the event of contamination, the risk of the appearance of cases and/or clusters within the French population therefore remains very low.
In France, active surveillance to identify the presence of the polio virus
Despite the elimination of poliomyelitis from the European region, great vigilance vis-à-vis a possible reintroduction of poliovirus is necessary. Indeed, endemic foci linked to the wild virus persist in the world (Pakistan and Afghanistan). The challenge is therefore to maintain high vaccination coverage until the disease has been eradicated.
Public Health France has set up a poliomyelitis surveillance program which is based on the one hand on compulsory notification (in place since 1936) and on the other hand, on reinforced surveillance of enteroviruses since 2000, in collaboration with the Center national reference for enteroviruses, and based on a network of voluntary laboratories.
Since the establishment of the enterovirus surveillance network in 2000, only vaccine polioviruses as well as a type 2 cVDPV, without recovery of virulence, all imported, have been detected in clinical samples, without any sign of infection. call that could evoke poliomyelitis in the patients sampled.
Health authorities in France remain vigilant regarding the risk of introduction of poliovirus strains derived from the vaccine linked to people from countries in which the oral polio vaccine is still used. Clinical and biological surveillance coordinated by the CNR for Enteroviruses and Parechoviruses makes it possible to detect any clinical suspicion requiring rapid action aimed at limiting the risk of transmission. Catch-up vaccination in unvaccinated or insufficiently vaccinated population groups is also important to prevent outbreaks of transmission from imported cases.
1 Polio: What do we know about the polioviruses detected in the UK? BMJ 2022;377:o1578 – Immediate actions in response to detection of vaccine derived polio virus type 2 (VDPV2) in London sewage samples
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