Traces of a form of polio derived from a vaccine strain have been found in sewage samples taken from a London sewage treatment plant, the World Health Organization and British authorities announced on Wednesday.
“It is important to note that the virus was isolated only from environmental samples – no associated cases of paralysis were detected,” the WHO said in a statement.
The WHO considers it “important that all countries, especially 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 quick response”.
According to the WHO, “any form of poliovirus, wherever 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 recent years due to low vaccination rates in some communities.
A wastewater treatment plant
Circulating vaccine-derived polioviruses type 2 (cVDPV2) are the most prevalent, according to the Global Polio Eradication Initiative, a public-private partnership led by national governments with six major partners including the WHO.
The British Health Safety 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 plant covers a large area in the north and east of the British capital, covering a population of nearly 4 million.
In recent years, an average of 1-3 poliovirus isolates per year 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.
No more OPV since 2004
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.
Poliomyelitis is a highly contagious disease that invades the nervous system and can cause permanent paralysis.