Polio outbreak detected in north and east London sewage
- Credit: PA
People are being urged to make sure their polio vaccines are up to date after the virus was detected in sewage from north and east London.
The UK Heath Security Agency (UKHSA), working with the Medicines and Healthcare products Regulatory Agency (MHRA), found poliovirus in samples collected from the Beckton Sewage Treatment Works in Newham, which serves around four million people.
Polio - officially eliminated in the UK in 2003 - can cause paralysis in rare cases and can be life-threatening.
While it is normal for traces of polioviruses to be found as isolated cases and not detected again, experts have raised the alarm after several genetically-linked viruses were picked up in samples between February and May.
Previously, it has been detected when a person 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.
However, the virus in the recent samples has evolved and is now classified as a "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.
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This means it can be spread more easily to people who are unvaccinated and who come into contact with either the faeces or coughs and sneezes of someone who is infected.
The UKHSA is working on the theory that a person vaccinated for polio abroad - possibly in Afghanistan, Pakistan or Nigeria - entered the UK early this year and was shedding the virus.
That person may have now passed it onto other, closely linked people in north-east London, who in turn are shedding the virus in their faeces.
Experts are looking at the possibility that just one family or extended family may be affected, though it is unclear how many people need to be infected for polio to be detected in sewage samples.
The UKHSA stressed that the virus has only been detected in sewage samples and no cases of paralysis have been reported.
It is now investigating the extent of community transmission and has established a "national incident" to check for cases elsewhere as a precaution.
UKHSA consultant epidemiologist Dr Vanessa Saliba said: “Vaccine-derived poliovirus (VDPV) is rare and the risk to the public overall is extremely low.
“VDPV has the potential to spread, particularly in communities where vaccine uptake is lower."
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 between one in 100 and 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.
Medics have now been alerted by UKHSA to look out for signs of polio paralysis.
The polio vaccine is given on the NHS when a child is eight, 12 and 16 weeks old as part of the 6-in-1 vaccine.
It is given again at three years and four months old as part of the 4-in-1 pre-school booster, and at age 14 as part of the 3-in-1 teenage booster.
A person needs to have received all of these vaccines to be fully vaccinated, though babies who have had two or three doses will have substantial protection.
Urgent medical attention should be sought if people experience rapid onset of weakness in a limb, which will be floppy, or difficulties with breathing.
The last case of natural polio infection in the UK was in 1984.
The UK stopped using live OPV in 2004 and switched to inactivated polio vaccine (IPV).