LONDON, June 22. /TASS/. The UK health authorities have declared a national incident after a poliomyelitis virus was detected in samples from London’s sewerage system, the UK Health Security Agency (UKHSA) said in a press release on Wednesday.

The UKHSA reported that some waste samples from the London Beckton Sewage Treatment Works, east London, had tested positive for a ‘vaccine-derived’ poliovirus type 2 (VDPV2), between February and May. The company serves around four million people in north and east London. The UKHSA added that each year one to three ‘vaccine-like’ polioviruses are normally detected in UK sewage samples.

"These previous detections occurred when an individual vaccinated overseas with the live oral polio vaccine (OPV) returned or travelled to the UK and briefly ‘shed’ traces of the vaccine-like poliovirus in their feces," the press release says.

According to the UKHSA, it marks the first time when a cluster of genetically-linked samples has been identified, unlike the common practice.

Sky News said that "most people with polio will not have any symptoms." Poliomyelitis spreads from person to person mostly through the fecal-oral route, or less frequently, through a common carrier (contaminated food or water), and then multiplies in the intestine.

Available vaccines

The UK health authorities pointed out that the poliovirus "on rare occasions can cause serious illness, such as paralysis, in people who are not fully vaccinated." The UK confirmed the last case of wild polio in 1984. In 2003 the country was declared polio-free. The UK replaced oral polio vaccine with inactivated polio vaccines in 2004. Nevertheless, some countries, including Pakistan, Afghanistan and Nigeria, continue to use the oral polio vaccine, while large numbers of immigrants from those countries live in the UK.

The UK’s routine vaccination program provides for three shots of an inactivated polio vaccine to be administered to children before the age of one. Thus, 95% of the British children have had their course of three vaccines by the age of two. In London, where this virus has been detected, the number is below 90%. The UKHSA calls on unvaccinated Britons to book a vaccination.

Oral polio vaccine has a fundamental difference from inactivated polio vaccine, as modified poliovirus vaccine strains can be excreted from the gastrointestinal tract for six weeks after vaccination. It may lead to a vaccine-derived poliovirus both in the vaccinated person (in immunodeficient individuals) and in unvaccinated contacts.