The poliovirus has been found in sewage samples collected from the London Beckton Sewage Treatment Works, officials from the UK Health Security Agency (UKHSA) said on Wednesday.
The virus that causes polio was eliminated in the UK by 2003 and the last case of wild polio was confirmed in 1984.
According to the UKHSA, it is normal for 1 to 3 ‘vaccine-like’ polioviruses to be detected each year in UK sewage samples but these have always been one-off findings that were not detected again. These previous detections occurred when an individual vaccinated overseas with the live oral polio vaccine (OPV) returned or travelled to the UK and briefly ‘shed’ traces of the vaccine-like poliovirus in their faeces.
Between February and May, several closely related viruses were found in sewage samples, alerting the UKHSA and ensuing an investigation.
Officials have said that the virus has continued to evolve and is now classified as a ‘vaccine-derived’ poliovirus type 2 (VDPV2), which on rare occasions can cause serious illness, such as paralysis, in people who are not fully vaccinated.
The UK Health Security Agency (UKHSA) believe that the virus was probably imported to London by someone who was recently vaccinated overseas with a live form of the virus.
Wastewater surveillance has been expanded to assess the extent of transmission and identify local areas for targeted action.
“Vaccine-derived poliovirus is rare and the risk to the public overall is extremely low,” said Dr Vanessa Saliba, Consultant Epidemiologist at UKHSA.
“Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower. On rare occasions it can cause paralysis in people who are not fully vaccinated,” she added.
Health authorities have declared a national incident and informed the World Health Organization (WHO) of the situation.
Polio is a rare disease and is most often spread from poor hygiene practices, including poor handwashing practices and consuming food or water that has been contaminated by faeces, informs Unicef.