Polio has been found in sewage samples in the British capital London – the first sign since the 1980s that the virus could spread in the country – but no cases have been found, authorities say.
The risk of infection from the disease, which causes paralysis in children in less than 1 percent of cases, was also low due to high vaccination coverage, the UK Health Security Agency (UKHSA) said.
The agency nevertheless encouraged parents to ensure their children were vaccinated after the virus was discovered during routine wastewater monitoring, especially those who may have missed shots during the COVID-19 pandemic.
Vaccination coverage in the UK is above the 90 percent needed to prevent outbreaks, but the range in London among children under two has fallen below that level in recent years.
The city’s National Health Service will contact parents of children under five who have not been vaccinated.
Polio mainly spreads through fecal contamination, killing and paralyzing thousands of children yearly.
There is no cure, but vaccination brought the world close to ending the disease’s wild or naturally occurring form.
UKHSA said it usually finds between one and three poliovirus samples in sewage each year, but they were more likely to be one-offs.
One sample was found at the Beckton Treatment Works in east London in February this year. Since April, there has also been ongoing detection at the same factory, which serves around four million people.
In the past, UKHSA said the detections occurred when a person vaccinated with the live oral polio vaccine abroad returned or traveled to the country, briefly passing the virus in his stool.
They believe this has also happened this time, the main difference being that the virus probably also spread between closely related humans and evolved into what is known as “vaccine-derived poliovirus,” which can cause illness.
Investigations into community transmission were ongoing, the agency said.
While events like this are virtually unheard of in the UK, the vaccine-derived poliovirus is a known, albeit rare, threat worldwide in low-vaccination countries.
It can cause outbreaks, and Ukraine and Israel have recently reported cases.
Outbreaks are more common in countries like Nigeria and Yemen.
The last case of polio in the UK was in 1984, and “wild” polio is now only found in Afghanistan and Pakistan, with imported outbreaks in Malawi and Mozambique in 2022.
The director-general of the World Health Organization, Tedros Adhanom Ghebreyesus, said the agency was working with the UK on the response.
“Monitoring, vaccination, and investment to end polio are critical,” he tweeted.