LONDON — The United Kingdom has declared a rare “national incident” after traces of the highly contagious poliovirus were found in sewage in London, the government said.
Britain, like many developed nations, has been largely polio-free since the 1980s because of a high rate of vaccination. So far, no cases have been reported.
However, its health security agency and medical regulator said in a statement Wednesday that authorities had found traces of poliovirus in sewage samples collected from the London Beckton Sewage Treatment Works, as part of “routine surveillance.” The sewage treatment plant covers a population close to 4 million in the north and east of the capital.
“Investigations are underway after several closely-related viruses were found in sewage samples taken between February and May,” the statement said.
The detection suggests it is likely “there has been some spread between closely-linked individuals in North and East London and that they are now shedding the type 2 poliovirus strain in their faeces,” the statement said.
The type 2 vaccine-derived poliovirus — as opposed to the wild or naturally occurring strain — is a weakened form of the live virus used in oral polio vaccines. Many countries, including the U.K. and United States, have moved away from using the oral vaccine as it can spread to unvaccinated people. But it remains common in nations such as Pakistan, Afghanistan and Nigeria.
The vaccine-derived poliovirus detected in the U.K. “on rare occasions can cause serious illness, such as paralysis, in people who are not fully vaccinated,” the British health authorities said.
So far, the poliovirus has only been detected in sewage samples but investigations are underway to establish whether any community transmission is occurring.
The United Kingdom was declared polio-free by the World Health Organization in 2003 and the last case of wild or naturally occurring polio contracted was in 1984, according to the government.
“Vaccine-derived poliovirus is rare and the risk to the public overall is extremely low,” Vanessa Saliba, consultant epidemiologist at UK Health Security Agency, said 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,” she said, adding that “no cases have been reported or confirmed so far.”
Polio, or poliomyelitis, is a crippling and potentially fatal infectious disease, which invades the nervous system and spreads mainly through contamination of fecal matter.
There is no cure, but vaccinations since the 1960s, mostly in childhood, have been a game changer allowing many countries to eradicate wild polio. The U.K. maintains vaccine coverage of more than 95 percent, the government said, largely through a routine childhood immunization program.
Surveillance, vaccination and investment to #EndPolio 🌍 is critical, as the #UK‘s announcement of environmental #polio samples identified in London sewage reminds us. No child has been infected so far. @WHO is supporting 🇬🇧 and partners.https://t.co/97zNVNUiBg
— Tedros Adhanom Ghebreyesus (@DrTedros) June 22, 2022
The U.K. health security agency says it normally detects between one and three “poliovirus isolates per year” in sewage but they are normally one-offs and unrelated to each other. “In this instance, the isolates identified between February and June 2022 are genetically related. This has prompted the need to investigate the extent of transmission,” it added.
The most likely scenario is that a recently vaccinated individual entered the U.K. from a country where an oral polio vaccine was used. The U.K. stopped such oral vaccines in 2004, authorities said.
WHO Director General Tedros Adhanom Ghebreyesus tweeted that “surveillance, vaccination and investment to #EndPolio is critical,” following news of the U.K. announcement.
The Global Polio Eradication Initiative, which works to end all wild and vaccine-related cases of the virus, said although largely eradicated, the disease remains endemic in Afghanistan and Pakistan.
“It is important that all countries, in particular those with a high volume of travel and contact with polio-affected countries and areas, strengthen surveillance in order to rapidly detect any new virus importation and to facilitate a rapid response,” the group said in a statement.
Meanwhile, health officials in London are urging parents to ensure young children are fully vaccinated to prevent any outbreak. The National Health Service will begin reaching out to parents of children aged under 5 in the capital who are not up to date with their vaccinations, the government said.