Traces of a form of polio found in London’s sewage

Traces of a form of poliomyelitis derived from a vaccine strain have been found in samples of waste water taken from a London sewage treatment plant. This was announced on Wednesday by the World Health Organization (WHO) and the British authorities. “It is important to note that the virus was isolated only in environmental samples – no associated case of paralysis was detected”, notes the UN organization.

WHO considers it “important that all countries, especially those with a high volume of travel and contact with countries and areas affected by poliomyelitis, strengthen surveillance in order to rapidly detect any new virus importation and to facilitate a quick answer “. “Any form of poliovirus, wherever found, poses a threat to children everywhere.”

Poliomyelitis can cause permanent paralysis

Poliomyelitis is a highly contagious disease that invades the nervous system and can cause permanent paralysis. 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 recent years due to low vaccination rates in some communities.

Circulating vaccine-derived polioviruses type 2 (cVDPV2) are the most dangerous, according to the Global Polio Eradication Initiative, a public-private partnership led by national governments with six major partners including the WHO. 959 cases were confirmed worldwide in 2020.

Localized spread

The British Health Security Agency said on Wednesday that the “isolates” had been found “in multiple samples of sewage taken from a London sewage treatment plant between February and June. This station covers a wide area in the north and east of the British capital, covering a population of nearly 4 million.

“These results reveal that there may be localized spread of poliovirus, most likely among people who are not up to date with their polio vaccinations,” says polio specialist Kathleen O’Reilly. In recent years, an average of 1-3 poliovirus isolates have been detected in sewage samples in the UK. But these isolates were unrelated. In the present case, indicates the British health security agency, “the isolates (…) are genetically linked”, making it necessary to study the transmission of this virus in north-east London.

A vaccine that is not used in the UK

According to UK authorities, the most likely scenario is that a recently vaccinated individual entered the UK before February from a country where oral polio vaccine (OPV) has been used in vaccination campaigns. While the UK stopped using OPV in 2004, several countries, including Pakistan, Afghanistan and Nigeria, have continued to use OPV containing type 2 virus to control outbreaks.

OPV is made from an attenuated form of the live poliovirus which “we immunize by growing in the gut for a short time when it can be detected in the stool,” says Nicholas Grassly, a professor at the Imperial College London. “This virus can sometimes be transmitted and very rarely it (…) can cause an outbreak of vaccine-derived poliovirus,” he says, noting that OPV was replaced in the UK by an injectable inactivated vaccine in 2004. .

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