People are being urged to ensure their polio vaccines are up to date after an outbreak of the virus was found in UK sewage samples.
Polio, which was officially eradicated in the UK in 2003, can be debilitating and life-threatening in rare cases.
Britain’s Health Security Agency (UKHSA), in partnership with the Medicines and Healthcare Products Regulatory Agency (MHRA), has found polio in sewage samples collected by London’s Beckton Sewage Treatment Works, which serves around four million people in north and east London.
While it is normal for the virus to be picked up as isolated cases and not rediscovered, experts have sounded the alarm after several genetically related viruses were found in samples between February and May.
Previously, the virus was picked up when a person who had been vaccinated abroad with the live oral polio vaccine (OPV) returned to or traveled to the UK and briefly passed traces of the vaccine-like poliovirus in their faeces.
However, the virus in the most recent samples evolved in England and is now classified as ‘vaccine-derived’ poliovirus type 2 (VDPV2).
VDPV is a strain of the attenuated poliovirus originally found in the oral polio vaccine that has evolved over time to behave more like the ‘wild’ or naturally occurring virus.
This means it can be more easily transmitted to people who are unvaccinated and come into contact with an infected person’s feces or cough and sneeze.
The UKHSA is working on the theory that a person vaccinated abroad with the polio vaccine – possibly in Afghanistan, Pakistan or Nigeria – entered the UK in early 2022 and shed the virus.
That person has now passed it on to other closely linked people in north east London, who in turn are passing the virus into their faeces.
Vaccine-derived poliovirus is rare and the overall risk to the public is extremely low
dr Vanessa Saliba, UKHSA
Experts are exploring the possibility that only one family or extended family could be affected, although it’s 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 set up a “national incident” to look for other cases as a precaution.
Health Minister Sajid Javid said he was “not particularly concerned” about the detection of the poliovirus.
He told BBC Radio 4’s PM program that UKHSA “reminds me that as a country we have very high immunization rates against polio. We’ve been declared polio-free since 2003 and haven’t had a case since.”
The polio vaccine is given by the NHS as part of the 6-in-1 vaccine when a child is eight, 12 and 16 weeks old. It is given again as part of the 4-in-1 (DTaP/IPV) preschool refresher at age 3 years and four months and as part of the 3-in-1 (Td/IPV) teen refresher at age 14.
All of these vaccines must have been given for a person to be fully vaccinated, although babies who have received two or three doses have significant protection.
Most of the UK population will be immune to vaccination during childhood, but in some communities with low immunization coverage, individuals may remain at risk
dr Vanessa Saliba, UKHSA
Latest figures show that in the UK almost 95% of children by the age of two have received the correct number of doses. However, this drops to just under 90% in London.
As for the pre-school boosters, only 71% of children in London had them by the age of five.
dr Vanessa Saliba, Consulting Epidemiologist at UKHSA, said: “Vaccine-derived poliovirus is rare and the risk to the general public is extremely low.
“Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower.
“On rare occasions, paralysis can occur in people who are not fully vaccinated. So if you or your child are not up to date on their polio vaccinations, it is important that you contact your GP to catch up or, if you are unsure, check your red book.
“Most of the UK population will be protected from vaccination during childhood, but in some communities with low immunization coverage, individuals may remain at risk.
“We are urgently investigating to better understand the extent of this transmission and the NHS has been asked to quickly report any suspected cases to the UKHSA, although no cases have been reported or confirmed to date.”
Most people who get polio have no symptoms, but some experience mild, flu-like problems such as a high temperature, extreme tiredness, headache, vomiting, stiff neck, and muscle aches.
Between one in 100 and one in 1,000 infections, the poliovirus 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.
When the respiratory muscles are affected, polio can become life-threatening.
Medical professionals have now been warned by the UKHSA to be on the lookout for signs of polio paralysis.
Urgent medical attention should be sought if patients develop rapid weakness in a limb that becomes flaccid, or have difficulty breathing.
The last acquired case of natural polio infection in the UK was in 1984.
The UK stopped using live oral polio vaccine (OPV) in 2004 and switched to inactivated polio vaccine (IPV).