Detection of circulating poliovirus-derived vaccine 2 (cVDPV2) in environmental samples – United Kingdom of Great Britain and Northern Ireland and the United States of America

Status at a glance

In the past few months, there have been several detections of sapin-like type 2 (SL2) poliovirus from environmental samples in the United Kingdom of Great Britain and Northern Ireland (hereinafter the United Kingdom) and the United States of America.

In the United Kingdom, since February 2022, the World Health Organization’s Global Polio Laboratories Network (GPLN) located at the National Institute for Biological Standards and Control (NIBSC) in London, has consistently detected Sabin-like isolates of type 2 poliovirus in water samples. Sewer collected from London. Samples collected on May 24 and 31 have enough mutations to qualify for a type 2 poliovirus (VDPV2) vaccine. Then, as the new virus was detected more than two months later, these samples were classified as ‘circulating’ VDPV2 on August 8. As of 5 September, no human case associated with VDPV2 has been reported in the UK.

In the USA, Sabin-like poliovirus type 2 was consistently detected in environmental samples collected from April 21 to August 26, 2022 from Rockland County, New York State, and adjacent counties. In late July, a case of VDPV2 was reported in an unvaccinated individual in Rockland County, who had developed paralysis. The case had no recent history of international travel. This is the first case of polio reported in the country since 2013. Because environmental viral sequences (collected on August 3 and August 11) were detected containing more than five nucleotide changes, both of which are associated with the case reported in Rockland County – These viruses are now classified as “circulating” VDPV2.

Virus detected in environmental samples in New York State, USA is genetically related to viruses detected in sewage samples from London, UK and in sewage samples collected between January and June 2022 from the Jerusalem area, Israel1.

Figure 1: Detection of genetically related cVDPV2 isolates in the UK and USA from February to August 2022

Epidemiology of polio

Polio is a highly contagious disease that mostly affects children under five years of age, causing permanent paralysis (about 1 in 200 infections) or death (5-10% of paralyzed people).

The virus is transmitted from person to person, mainly by fecal-oral route or, less often, by common medium (such as contaminated water or food) and multiplies in the intestine, where it can invade the nervous system and cause paralysis and death. Initial symptoms of polio include fever, fatigue, headache, vomiting, stiff neck, and pain in the extremities. In a small percentage of cases, the disease causes paralysis, which is often permanent. There is no cure for polio, but it can be prevented with vaccination.

The incubation period is usually 7 to 10 days but can range from 4 to 35 days. Up to 90% of those infected are either asymptomatic or have 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 found in the oral polio vaccine (OPV). The oral polio vaccine contains a live attenuated form of the polio virus. In rare cases, when breeding in the GI tract, oral vaccine strains are genetically altered and may spread in communities that have not been fully immunized against polio, especially in areas with poor hygiene, poor sanitation, or overcrowding. Other changes occur as these viruses spread from person to person. The lower the immunity of the population, the longer this virus will survive and the more genetic changes it will undergo. In very rare cases, a vaccine-derived virus can mutate genetically into a form that can paralyze – this is known as a vaccine-derived polio virus (VDPV).

Detection of VDPV in at least two different sources and at least 2 months apart, genetically related, indicative of community transmission, should be classified as ‘circulating’ vaccine-derived poliovirus type 2 (cVDPV2). cVDPV2 continues to affect different regions of the world.

The World Health Organization, in coordination with national authorities, will continue to assess the genetic and epidemiological situation to determine the potential spread of the virus and the potential risks associated with these isolates detected from various locations around the world.

  • UK public health measures

The UK Health Security Agency (UKHSA) is carrying out further investigations including assessing public health risks and implementing response measures. These measures include:

  • Strengthening environmental, clinical and laboratory monitoring of polio.
  • An offset campaign targeting children under 5 years of age was implemented in London in June 2022, and a supplementary booster campaign for inactivated polio vaccine (IPV) targeting children aged 1 to 9 years was launched in London in August 2022.
  • Public health professionals, health professionals and laboratory personnel have been alerted to the discovery of VDPV2 in London.
  • Remind health professionals of the importance of screening of newly registered children and routine immunizations of adults, focusing on the unvaccinated population (new migrants, asylum seekers and refugees).
  • Local and regional laboratories have requested that all enterovirus-positive stool samples be referred to UKHSA.
  • Enhanced environmental sampling to assess the extent of the virus spread across London. In addition, a set of additional wastewater sampling sites are being established across the country.

  • Public health measures in the United States of America
    • Strengthening polio wastewater control.
    • Ongoing activities to support polio vaccination and increase vaccination coverage in Rockland and Orange counties in New York State. Planning is underway to launch an immunization campaign to provide IPV to residents of Rockland County who may have been exposed to the polio virus.
    • Conducting polio virus testing in wastewater samples in New York and neighboring countries, as well as providing confirmatory testing for clinical samples.
    • Coordination of acute flaccid myelitis myelitis (AFM) surveillance throughout the USA and strengthening of surveillance of paralytic and non-paralytic polio in areas where poliovirus has been detected in wastewater.
    • Health guidelines including information on polio, the status in New York State, and polio immunization, have been released to health providers and hospitals across the state and in the case county directly.
    • On September 9, a state of emergency was declared for a polio disaster in New York State. The advertisement allows additional health professionals, such as pharmacists, to administer the polio vaccine and allows health practitioners to issue standing orders for polio vaccinations.

The emergence of cVDPV2 in the UK and USA is a reminder that until polio is eradicated, polio-free countries will remain at risk of polio recurrence or re-emergence. The discovery of this VDPV2 strain underscores the importance of;

• Maintain high levels of routine polio immunization coverage at all levels and in all communities to reduce the risks and consequences of any circulation of polio virus.

• Existence of sensitive monitoring systems for timely detection of VDPV import or VDPV emergence.

Based on WHO and UNICEF estimates, vaccine coverage for three routine doses of polio vaccine evaluated in children aged 12 months in the UK and USA was 93% and 92%, respectively, in 2021.

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

WHO reaffirms to all Member States the importance of reaching and maintaining polio vaccination coverage of over 95% in every district or municipality; Maintaining high quality for three key surveillance indicators: acute flaccid paralysis rate (AFP), percentage of cases investigated within 48 hours, and percentage of cases with an adequate sample; Improve complementary (environmental and enterovirus) surveillance of poliovirus and update national poliovirus outbreak response plans in order to quickly detect and respond to new imports or emergence of VDPV to reduce consequences of poliovirus transmission and facilitate rapid response.

The The 32nd International Emergency Committee for the International Health Regulations for Polio The June 2022 meeting agreed, under the International Health Regulations (2005), that the risk of international spread of poliovirus remained a Public Health Emergency of International Concern (PHEIC) and recommended that the interim recommendations be extended for a further three months.