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Situation at a glance 
In the past few months, there have been several genetically linked Sabin-like type 2 poliovirus (SL2) detections from environmental samples in the United Kingdom of Great Britain and Northern Ireland (hereafter the United Kingdom) and the United States of America.
In the United Kingdom, since February 2022, the WHO Global Polio Laboratory Network (GPLN) located at the National Institute for Biological Standards and Control (NIBSC) in London has consistently detected Sabin-like type 2 poliovirus isolates in sewage samples collected from London. Samples collected on 24 and 31 May had sufficient mutations to qualify as vaccine derived polio virus type 2 (VDPV2). Subsequently, due to a new detection of the virus more than two months later, these samples were classified as ‘circulating’ VDPV2 on 8 August.  As of 5 September, no human case associated with VDPV2 has been reported in the United Kingdom.
In the United States of America, Sabin-like type 2 poliovirus has been consistently detected in environmental samples collected between 21 April to 26 August 2022 from Rockland County, New York State, and nearby counties. In late July, a case of VDPV2 was reported in an unvaccinated individual in Rockland County, who presented with paralysis. The case had no recent history of international travel. This is the first case of poliomyelitis reported in the country since 2013. Due to detection of environmental viral sequences (collected on 3 August and 11 August) containing more than five nucleotide changes, and both linked to the case reported in Rockland County – these viruses are now being classified as ‘circulating’ VDPV2.
The virus detected in environmental samples in New York State, United States of America is genetically linked to viruses detected in sewage samples from London, United Kingdom and in sewage samples collected between January to June 2022 from Jerusalem District, Israel1.

Figure-1 Detection of genetically linked cVDPV2 isolates in the United Kingdom and the United States of America from February to August 2022 

Epidemiology of Poliomyelitis 

Polio is a highly infectious disease that largely affects children under five years of age, causing permanent paralysis (approximately 1 in 200 infections) or death (5-10% of those paralyzed).

The virus is transmitted from person-to-person, mainly through the fecal-oral route or, less frequently, by a common vehicle (e.g., contaminated water or food) and multiplies in the intestine, from where it can invade the nervous system and cause paralysis and death. Initial symptoms of polio include fever, fatigue, headache, vomiting, stiffness of the neck and pain in the limbs. In a small proportion of cases, the disease causes paralysis, which is often permanent. There is no cure for polio but it can be prevented by immunization.

The incubation period is usually 7–10 days but can range from 4–35 days. Up to 90% of those infected are either asymptomatic or experience only mild symptoms and the disease often goes unrecognized.

Vaccine-derived poliovirus is a well-documented type of poliovirus that has mutated from the strain originally contained in the oral polio vaccine (OPV). The OPV contains a live, weakened form of poliovirus. On rare occasions, when replicating in the gastrointestinal tract, OPV strains genetically change and may spread in communities that are not fully vaccinated against polio, especially in areas where there is poor hygiene, poor sanitation, or overcrowding. Further changes occur as these viruses spread from person to person. The lower the population immunity, the longer this virus survives and the more genetic changes it undergoes. In very rare instances, the vaccine-derived virus can genetically change into a form that can paralyze – this is what is known as a vaccine-derived poliovirus (VDPV).

The detection of VDPV in at least two different sources and at least two months apart, that are genetically linked, showing evidence of transmission in the community, should be classified as ‘circulating’ vaccine-derived poliovirus type 2 (cVDPV2).  cVDPV2 continues to affect different areas of the world.

Public health response

 

WHO, in coordination with national authorities, will continue to evaluate the genetic and epidemiological situation to determine the possible spread of the virus and the potential risk associated with these isolates detected from different locations around the world.
  • Public health measures in the United Kingdom

The United Kingdom Health Security Agency (UKHSA) is conducting further investigations including assessing the public health risk and implementing response measures. These measures include:

  • Strengthening the environmental, clinical and laboratory surveillance for polio.
  • A catch-up campaign targeted at children aged less than 5 years of age in London was implemented in June 2022, and a supplementary booster inactivated polio vaccine (IPV) campaign targeting children aged 1 to 9 years in London was launched in August 2022.
  • Public health professionals, health professionals, and laboratory staff alerted to the detection of VDPV2 in London.
  • Health professionals reminded of the importance of checking newly registered children and adult routine immunizations are up-to-date, with an emphasis on under-immunized populations (new migrants, asylum seekers and refugees).
  • Local and regional laboratories requested to refer all enterovirus positive stool samples to the UKHSA.
  • Enhancing environmental sampling to assess the extent of the spread of the virus across London. In addition, a range of additional sewage sampling sites are being stood up across the country.

 

  • Public health measures in the United States of America
    • Enhancing polio wastewater surveillance.
    • Ongoing activities to support polio vaccination and increase vaccination coverage in Rockland and Orange Counties in New York State. Planning underway to launch an immunization campaign to provide IPV to residents of Rockland County who have potentially been exposed to poliovirus.
    • Conducting testing for poliovirus in wastewater samples in New York and neighbouring States, as well as providing confirmatory testing for clinical specimens.
    • Coordinating surveillance for Acute Flaccid Myelitis (AFM) throughout the United States of America and enhancing surveillance for paralytic and non-paralytic polio in areas where poliovirus has been detected in wastewater.
    • Health advisories including information on polio, the situation in New York State, and polio immunization, have been released to health providers and hospitals across the State and in the immediate county of residence of the case.
    • On 9 September, a state disaster emergency due to polio was declared in New York State. The declaration allows additional health professionals, such as pharmacists, to administer polio vaccine and allows health practitioners to issue standing orders for polio vaccinations.

 

WHO risk assessment

The emergence of cVDPV2 in the United Kingdom and in the United States of America is a reminder that until polio is eradicated, polio-free countries will remain at risk of polio re-infection or re-emergence. The detection of this VDPV2 strain underscores the importance of;

 

• maintaining high levels of routine polio vaccination coverage at all levels and in all communities to minimize the risk and consequences of any poliovirus circulation.
• having sensitive surveillance systems for the timely detection of VDPV importation or VDPV emergence.

 

Based on the WHO UNICEF estimates, the vaccine coverage for three routine doses of polio vaccine evaluated in children aged 12 months in the United Kingdom and United States of America were 93% and 92% respectively in 2021.

WHO will continue to support the ongoing investigation, risk assessment and outbreak response by national authorities.

 

WHO advice

WHO reiterates to all Member States the importance of reaching and maintaining polio vaccination coverage of more than 95% in each district or municipality; maintaining high quality for three main surveillance indicators: acute flaccid paralysis (AFP) rate, percentage of cases investigated within 48 hours, and percentage of cases with an adequate sample; optimizing supplementary (environmental and enterovirus) poliovirus surveillance and updating national poliovirus outbreak response plans in order to rapidly detect and respond to new virus importations or VDPV emergence to minimize the consequences of poliovirus transmission and facilitate a rapid response.

The thirty-second polio IHR Emergency Committee meeting held in June 2022, convened under the International Health Regulations (2005), agreed that the risk of international spread of poliovirus remains a Public Health Emergency of International Concern (PHEIC) and recommended the extension of Temporary Recommendations for a further three months.

Further information

Citable reference: World Health Organization 14 September 22 2022). Disease Outbreak News; Detection of circulating vaccine derived polio virus 2 (cVDPV2) in environmental samples– the United Kingdom of Great Britain and Northern Ireland and the United States of America . Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2022-DON408

 

[1] No further information is available on VDPV2 detections in Israel at this stage as investigations are ongoing

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