A type of poliovirus derived from vaccines has been discovered in sewage samples in London, the World Health Organization and British health officials said on Wednesday, adding that more analysis was underway.
There have been no human cases of polio found in Britain, where the crippling disease was completely eradicated two decades ago.
The WHO said in a statement that “type 2 vaccine-derived poliovirus (VDPV2)” was found in environmental samples in the British capital.
“It is important to note that the virus is only isolated from environmental samples,” it said, emphasizing that “no associated cases of paralysis have been detected.”
But it warned, “any form of poliovirus anywhere is a threat to children everywhere.”
A massive worldwide effort in recent decades has come close to eradicating polio, a crippling and potentially fatal viral disease that particularly affects children under the age of five.
Cases have decreased by 99 percent since 1988, when polio was endemic in 125 countries and 350,000 cases were recorded worldwide.
The wild-type version of the virus now exists only in Afghanistan and Pakistan, but a type of vaccine that weakens smallpox but contains live polio still causes occasional outbreaks elsewhere.
‘Check vaccination history’
Oral polio vaccine (OPV) replicates in the gut and can be passed on to others through fecal-contaminated water – meaning that it will not harm the vaccinated child, but can infect their neighbors in places where hygiene and immunization levels are low.
While weaker than wild poliovirus, this variant can cause serious illness and paralysis in people who are not vaccinated against the disease.
Worldwide, there were 959 confirmed cases of VDPV2 by 2020, according to the WHO.
Polio eradication expert Kathlene O’Reilly warned on Wednesday that the discovery in the London sewer samples suggests “there may be local spread of poliovirus, probably within individuals unaware of polio immunizations”.
“The most effective way to prevent further spread is to check vaccination history, especially of young children, to check that polio vaccination has been recorded,” she said.
Polio immunization coverage in London stands at nearly 87 percent, the WHO said.
The UN health agency has called for OPV to be phased out worldwide and replaced by inactivated polio vaccine (IPV).
Britain stopped using OPV in 2004, and British health authorities said it was likely the virus found in the sewage samples had been imported by someone who had recently been vaccinated abroad.
‘We are not isolated’
David Elliman, a consultant pediatrician at Great Ormond Street Hospital, said parents sometimes ask why vaccines are continued to be given against diseases that have been eliminated in the UK, such as polio.
“The answer is that even though we are an island, we are not isolated from the rest of the world, which means diseases can be brought in from abroad,” he said.
“The discovery of vaccine-derived poliovirus in sewage proves the point.”
The UK Health Security Agency (UKHSA) said the virus isolates were found in “multiple sewage samples collected from the London Beckton Sewage Treatment Works between February and June 2022.”
The plant covers a large area of north and east London that is home to about four million people.
A few isolates of poliovirus are detected each year on average in sewage samples in the UK, but they are not related, health authorities said, warning that in this case the isolates were “genetically related”.
“This necessitates an investigation into the extent of transmission of this virus in north-east London,” said UKHSA.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)