A type of poliovirus derived from vaccines has been detected in London sewage samples, the World Health Organization and British health officials said on Wednesday, adding that more analysis is underway.
No human cases of polio have been 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)” had been found in environmental samples in the British capital.
“It is important to note that the virus has only been isolated from environmental samples,” it said, emphasizing that “no concomitant cases of paralysis have been detected.”
But it warned, “any form of poliovirus anywhere is a threat to children everywhere.”
A massive global effort has come close in recent decades to eradicate polio, a crippling and potentially deadly viral disease that mainly affects children under the age of five.
Cases have dropped 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 containing small amounts of attenuated but live polio still causes occasional outbreaks elsewhere.
Check Vaccination History
Oral polio vaccine (OPV) replicates in the gut and can be transmitted to others through fecal contaminated water – meaning that it does not hurt the vaccinated child, but can infect their neighbors in places where hygiene and immunization levels are low.
Although weaker than wild poliovirus, this variant can cause serious illness and paralysis in people who have not been vaccinated against the disease.
Worldwide, there were 959 confirmed cases of VDPV2 in 2020, according to the WHO.
Polio eradication expert Kathlene O’Reilly warned on Wednesday that the discovery in the London sewage samples suggests that “there may be localized spread of poliovirus, most likely within individuals who are not up to date with polio vaccinations”.
“The most effective way to prevent further spread is to check vaccination history, especially of young children, to make sure polio vaccination is included,” she said.
Polio immunization coverage in London stands at nearly 87 percent, the WHO said.
The UN’s health agency has called for OPV to be phased out worldwide and replaced with inactivated polio vaccine (IPV).
Britain stopped using OPV in 2004, and British health authorities said it was likely that the virus found in the sewage samples had been introduced by someone who had recently been vaccinated abroad with it.
“We are not isolated”
David Elliman, a consultant pediatrician at Great Ormond Street Hospital, said parents sometimes ask why vaccines are still being 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 that diseases can be brought in from abroad,” he said.
“The finding 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 part of north and east London which is home to about four million people.
A few poliovirus isolates are detected in British sewage samples on average each year, but they tend to be unrelated, health authorities said, warning that the isolates in this case are “genetically related”.
“This has led to an investigation into the extent of the transmission of this virus in north-east London,” UKHSA said.
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