LONDON, June 22 (Xinhua) -- Poliovirus has been detected in sewage samples from North and East London taken between February and May, the UK Health Security Agency (UKHSA) said Wednesday.

Health officials are now concerned about the community spread of the virus after several closely-related polio viruses were found in sewage samples from the London Beckton Sewage Treatment Works taken between February and May, but have stressed the risk to the public is extremely low.

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 detection of a VDPV2 suggests that it is likely there has been some spread between closely-linked individuals in North and East London and that they are now shedding the type 2 poliovirus strain in their faeces, said the agency.

"Vaccine-derived poliovirus is rare and the risk to the public overall is extremely low," Dr Vanessa Saliba, consultant epidemiologist at UKHSA, said in a statement. "Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower. "

The last case of wild polio contracted in Britain was confirmed in 1984. The country was declared polio-free in 2003.

David Heymann, professor of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, said: "Vaccine derived polio virus is now present in many countries around the world. The virus results from a mutation of the Sabin virus that is a live virus used to vaccinate against polio, and it causes paralysis in some, though the majority of infections are asymptomatic."

"The fact that it has been found in sewage in the UK attests to the strength of the surveillance programmes of UKHSA. Its presence in the sewage reminds us that polio eradication has not yet been completed in the world," said the epidemiologist.