Almost a million children aged one to nine in London are to be offered a polio vaccine.

Since it was detected at Beckton Sewage Treatment Works, Poliovirus has been found 116 times in sewage in Barnet, Brent, Camden, Enfield, Hackney, Haringey, Islington and Waltham Forest.

There have been no confirmed cases.

The vaccine rollout will be a booster or catch-up dose in a bid to stop the spread of the virus and prevent cases of paralysis.

Families will be contacted by the NHS, and areas where the virus has been found will be targeted first.

Vaccination rates are lower in the capital compared to the rest of the country. In the UK, almost 95 per cent of children have had the correct number of doses. However, this drops to just under 86.6pc in London.

The UK stopped using live oral polio vaccine in 2004 and switched to inactivated polio vaccine.

However, it is used elsewhere in the world and recent samples in London suggest there has been “some virus transmission”.

The virus detected

Some of the virus found in recent samples has been classified as vaccine-derived poliovirus type 2 (VDPV2). VDPV is a strain of the weakened poliovirus, that was initially included in the oral polio vaccine, which has changed over time and behaves more like the “wild” or naturally occurring virus.

This means it can be spread more easily to people who are unvaccinated and who come into contact with the faeces or coughs and sneezes of an infected person.

On rare occasions, VDPV2 can lead to cases of paralysis in unvaccinated people.

Symptoms

Most people who get polio do not have symptoms but some suffer mild, flu-like issues such as a high temperature, extreme tiredness, headaches, vomiting, a stiff neck and muscle pain.

In one in 100 to one in 1,000 infections, the polio virus attacks the nerves in the spine and base of the brain.

This can cause paralysis, usually in the legs, that develops over hours or days.

If the breathing muscles are affected, polio can be life threatening.

The last case of natural polio infection acquired in the UK was in 1984.

New York

The UK Health Security Agency is working with health agencies in New York and Israel to investigate whether there are links between incidents in these countries.

Officials in New York announced that they had a confirmed case of paralytic polio in an unvaccinated person in July.

And global health officials have now confirmed the case is “genetically linked” to the samples from sewage detected both in London and Jerusalem.