Public Health France maintains its vigilance

In June 2022, Public Health France published an update and a risk analysis following the prolonged detection of polioviruses derived from a type 2 vaccine strain (VDPV2), in samples of wastewater taken from the station. Beckton sewage treatment plant, draining a catchment population of 4 million people from North East London.

Since then, a case of poliomyelitis in VDPV2 was reported by the CDC on July 18, 2022 in an unvaccinated adult living in the state of New York and detection of genetically related polioviruses has been demonstrated retrospectively, in sewage from the county of residence of the patient. A state of emergency was declared by the Governor on September 9, 2022.

These two events are unusual and concerning, as they each reflect prolonged silent circulation of VDPV2 in communities where polio vaccination coverage is low.

Poliovirus: what do we know about the evolution of the English situation?

Update on the situation

Between February and May 2022, several viruses with a genetic profile of vaccine-derived poliovirus type 2 (VDPV2) viruses were detected in sewage from Beckton station in London.

Every year, pinpoint detections of poliovirus are seen in sewage monitoring in the UK. But, for the first time, surveillance data suggest circulation of VDPV2 in an under-vaccinated community¹, from a recently vaccinated person and from a country using the oral vaccine in its vaccination campaigns. The oral vaccine has not been used in the UK since 2004.

Viruses have only been detected in sewage samples and no cases of paralysis have been reported so far. Authorities consider the risk of spread to the general population to be low, although there is a risk of transmission in under-vaccinated communities. In Great Britain, the 3-dose vaccination coverage for vaccines including polio for infants was estimated at 86.6% at 12 months and 87.0% at 24 months in London.

What are the authorities’ recommendations?

The English authorities recalled the importance of checking and updating the vaccinations of people residing in London, and decided at the beginning of August, in addition to the catch-up campaign, to organize a vaccination campaign in London for young children. from 1 to 9 years of age regardless of their origin² by the inactivated vaccine (IPV), including in children already correctly vaccinated to limit the spread of the virus.

Poliovirus: what do we know about the American situation?

Update on the situation

On July 18, 2022, a case of poliomyelitis caused by vaccine-derived virus type 2 (cVPDV2) was reported in New York State in an unvaccinated young adult.³. This is the second case resulting from the circulation of a poliovirus derived from a vaccine strain (cVPDV type 1 in 2005), since the last declared case of poliomyelitis due to a wild poliovirus in the United States in 1979.

Retrospectively, sequences of VDPV2 genetically related to the case strain were detected in 50 environmental samples collected between May and July 2022 in Rockland County (county of residence of the polio patient; 31 positive samples) and 3 neighboring counties ( Orange, Sullivan, Nassau; 19 samples positive, suggesting VDPV2 transmission and circulation in under-vaccinated communities⁴.

These sequences are also genetically related to strains detected in environmental samples collected in London.

In addition, 4 samples taken from New York City also contain poliovirus type 2 sequences derived from vaccinia poliovirus type 2, but these sequences are not linked to the sequence from the polio patient.

According to the New York State Immunization Information System⁵3-dose immunization coverage for infants under 24 months was 67.0% in July 2020 in Rockland County and decreased to 60.3% in August 2022³it was 58.8% in Orange County, 62.3% in Sullivan County, and 79.15% in Nassau County in August 2022.

What are the authorities’ recommendations?

New York state authorities have declared a state of emergency.⁶ and reminded the need for each unvaccinated or insufficiently vaccinated New York State resident (including children from the age of 2 months, pregnant women and adults who have not previously received a complete regimen) to update their polio vaccination without delay. They also encourage recall for people at higher risk of infection, such as certain health professionals.⁷.

Poliovirus: what is the international situation?

Although Europe has been officially declared as a region free of wild polioviruses since 2002 by the WHO, Public Health France maintains its vigilance vis-à-vis possible reintroductions of polioviruses and monitors the evolution of the international situation within the framework of the global polio eradication initiative. Indeed, endemic foci linked to the wild virus type 1 persist in the world (Pakistan and Afghanistan). In addition, VDPV2 circulates in an epidemic manner in many countries of the world (Africa, Yemen, Afghanistan, Pakistan, Ukraine).

In the WHO-Europe region, rare cases of paralysis caused by circulating vaccine-derived poliovirus (cVDPV) viruses have recently been reported in Ukraine in October and December 2021 and in 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.

The risk of importing cVDPV in connection with people from Ukraine should be taken into account. Given sub-optimal vaccination coverage in Ukraine estimated at around 80% in 2021⁸the vaccination of refugees, infants and young children as well as the booster for adults, is a priority.

Poliomyelitis surveillance: what is the French situation?

A very low risk in sufficiently vaccinated populations

Given the risk of poliovirus importation, the challenge is therefore to maintain high vaccination coverage until the disease has been eradicated.

Indeed, there is no treatment for poliomyelitis. The main preventive measures relate to hygiene and vaccination, which has made it possible to reduce the incidence of poliomyelitis due to the wild virus by more than 99% worldwide.

What is the vaccination coverage in France?

France benefits from very high vaccination coverage against poliomyelitis (inactivated polio vaccine): 99% for primary vaccination and 96% for booster vaccination in infants in 2019. These figures have always been very high , the vaccine having been compulsory until the age of 12 until 2018. In addition, the vaccination is mandatory for infants born from 2018.

This excellent coverage is reassuring, providing 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 extremely low.

However, heterogeneity in primary vaccination coverage cannot be ruled out in certain regions or certain specific population groups with less use of the healthcare system (national and regional vaccination public health bulletin – April 2022).

Catch-up vaccination in unvaccinated or insufficiently vaccinated population groups is therefore important to prevent outbreaks of transmission from imported cases. The HAS recommends that migrant children arriving on French territory carry out a booster shot with a trivalent injectable inactivated polio vaccine⁹including if they have been properly vaccinated with the oral vaccine but have not previously received a dose of injectable inactivated polio vaccine.

Active surveillance to identify the presence of the polio virus

The last case of wild poliomyelitis was reported in France in 1995. Since the establishment of the enterovirus surveillance network in 2000, with the exception of accidental exposure in an industrial environment declared in 2018, only vaccine polioviruses, all imported as well as a type 2 cVDPV, without resumption of virulence detected in 2006, were demonstrated in clinical samples, without any warning signs that could suggest 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.

In view of recent events, communication with health professionals is underway to make them aware of this risk and remind them of the action to take in the event of any suspicion of poliomyelitis and in particular the virological research to be carried out by the CNR.