Sewage testing aims to pinpoint source of polio virus

probably imported from an individual who had recently had an oral polio vaccine abroad, possibly in countries such as Nigeria, Pakistan or Afghanistan where outbreaks are still common.

Oral vaccines contain live strains which can be shed and enter the sewage system.

The virus was picked up during routine fortnightly monitoring of sewage at London Beckton Sewage Treatment Works, which covers four million people, and more localised testing is now taking place in six other areas in the capital to try to pinpoint the outbreak. The UKHSA said that if a specific area was found they may target it with a mass vaccination programme to make sure communities are protected.

Jane Clegg, chief nurse for the NHS in London, said:“the majority of Londoners are fully protected against polio but the NHS will begin reaching out to parents of children aged under five in London who are not up-to-date.”

Britain began vaccinating against polio in 1955, and moved to a live oral vaccine in 1961. After the eradication of polio, Britain moved to an injectable inactivated vaccine in 2004, which does not shed into the sewage system.

Prof Paul Hunter, professor in medicine, UEA, said: “In populations with low vaccine uptake it is possible that the live polio vaccine can spread from one person to another.”

“If this is sustained, over time (one or two years) this vaccine-derived virus can mutate to become fully virulent again and can start to cause paralysis in people who have not been vaccinated.

“Vaccine-derived transmission events are well described and most ultimately fizzle out.”