Poliovirus testing is being carried out in the M1 corridor - including in Watford and Luton.
The UK Health Security Agency (UKHSA) announced on Friday, September 2 that sewage treatment works in Watford in Hertfordshire and Luton in Bedfordshire will be tested for traces of poliovirus.
It follows the discovery of the virus at Thames Water sewage works in Beckton, London, announced on June 22 this year.
The government's UKHSA has already carried out sampling in London and Glasgow. Although the virus was detected during sampling in the capital, nobody has reported being diagnosed with the disease.
Dr Vanessa Saliba, UKHSA consultant epidemiologist, said: "No cases of polio have been reported and for the majority of the population, who are fully vaccinated, the risk is low.
"We are now expanding the sewage sampling nationally to areas that are at highest risk of new poliovirus importations and areas most likely to see spread of poliovirus from London."
Along with poliovirus sampling in Watford and Luton, testing will also be rolled out in Birmingham, Blackburn with Darwen, Bradford and Leeds, Bristol, Brighton and Hove, Castle Point (Essex), parts of Greater Manchester (Manchester, Bury and Salford), Leicester, Liverpool, Nottingham, Preston, Sheffield and parts of Tyne and Wear (Newcastle upon Tyne, Gateshead and North Tyneside).
Since the initial find in Beckton, the UKHSA and the Medicines and Healthcare products Regulatory Agency have identified at least one positive sample of poliovirus in eight London boroughs.
These are Barnet and Enfield, which sit next to Hertfordshire, and Brent, Camden, Hackney, Haringey, Islington and Waltham Forest.
The government has offered all children aged one to nine in London a dose of the polio vaccine.
Jane Clegg, NHS London chief nurse, said: "While the majority of Londoners are protected from polio, the NHS is contacting parents of eligible children aged one to nine years old to offer them a top-up dose to ensure they have maximum protection from the virus.
"We are already reaching out to parents and carers of children who aren’t up to date with their routine vaccinations, who can book a catch-up appointment with their GP surgery now and for anyone not sure of their child’s vaccination status, they can check their Red Book."
According to the NHS, polio was eradicated in Europe in 2003.
The disease can cause mild, flu-like symptoms which usually last for 10 days, or - in rare cases - paralysis.
An NHS statement reads: "There have been no confirmed cases of paralysis due to polio caught in the UK since 1984."
Information about polio is on the NHS website: "There have been no confirmed cases of paralysis due to polio caught in the UK since 1984."
Information about polio is on the NHS website: https://www.nhs.uk/conditions/polio/
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