- UK health officials said Wednesday that "several" polioviruses were found in sewage samples between February and May.
- The find is raising concern that polio may have spread "between closely-linked individuals" in North and East London.
- No cases have been confirmed, and health officials say the risk to the public "is extremely low."
The UK Health Security Agency says it's possible that there may be "some spread" of polio happening in small clusters in London.
Wastewater samples taken from North and East London between February and May suggest that the crippling disease, which used to kill hundreds of people in the UK every year, could be circulating "between closely-linked individuals."
Experts are still cautious about this sewage finding, though, stressing that no polio cases have been confirmed in humans in the UK yet, so the extent of any polio outbreak — and whether one even exists — is unclear.
However, the presence of "several" different sewage samples that look quite similar to one another, virologically speaking, is giving investigators pause. (When people have polio, they can shed traces of it in their poop, so the contaminated sewage is a sign that some spread between people may already be happening in London.)
The UK has been considered polio-free since 2003, and almost everyone in the UK is protected from polio through routine childhood vaccinations.
Viral shedding explains why polio might be in the sewers
While wild polio has been near-eradicated around the world through widespread vaccination, people who've been recently immunized against the disease can shed the virus for a little while, as a result of their successful vaccination.
That viral shedding can in turn infect unprotected individuals around them who haven't been vaccinated yet.
"On rare occasions it can cause paralysis in people who are not fully vaccinated, so if you or your child are not up to date with your polio vaccinations it's important you contact your GP," Dr. Vanessa Saliba with the UKHSA said Wednesday in a statement.
"We are urgently investigating to better understand the extent of this transmission and the NHS has been asked to swiftly report any suspected cases to the UKHSA"
Polio can infect a person's spinal cord, making it crippling, or deadly, but many people show no outward symptoms, and it's possible to recover from some flu-like symptoms of the infection within a few days.
However, even people who make a full recovery from polio can go on to develop paralysis decades later in life, with post-polio syndrome.