Traces of a vaccine-derived form of polio have been found in sewage samples from a London sewage treatment plant, the World Health Organization and British authorities said on Wednesday.
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“It is important to note that the virus has only been isolated from environmental samples – no associated cases of paralysis have been identified,” the WHO said in a statement.
The WHO considers it “important that all countries, particularly those with high levels of travel and exposure to polio-affected countries and areas, increase surveillance to quickly detect any new virus importation and enable a rapid response.”
According to the WHO, “any form of poliovirus, wherever it is found, poses a threat to children everywhere”.
Wild poliovirus is the best-known form of poliovirus.
There is another form of poliovirus that can spread within communities: circulating vaccine-derived poliovirus, or cVDPV. Although cVDPVs are rare, they have become more common in some communities in recent years due to low vaccination rates.
Circulating vaccine-derived poliovirus type 2 (cVDPV2) is the most prevalent, according to the Global Polio Eradication Initiative, a public-private partnership led by national governments with six key partners including WHO.
In 2020, 959 cases were confirmed worldwide.
The British Health Security Agency said on Wednesday that the “isolates” “had been found in several sewage samples taken from a London sewage treatment plant between February and June. This station covers a wide area to the north and east of the British capital and covers a population of almost 4 million.
In recent years, an average of 1-3 poliovirus isolates per year have been detected in wastewater samples in the UK. But these isolates were not related to each other. In the present case, the British health authority indicates that “the isolates (…) are genetically linked”, making it necessary to investigate the transmission of this virus in north-east London.
According to UK authorities, the most likely scenario is that a recently vaccinated person entered the UK before February from a country where oral polio vaccine (OPV) was used in vaccination campaigns.
While the UK stopped using OPV in 2004, several countries including Pakistan, Afghanistan and Nigeria continue to use OPV, which contains type 2 viruses, to control outbreaks.
Poliomyelitis is a highly contagious disease that invades the nervous system and can cause permanent paralysis.