The UK has declared a national incident after detecting poliovirus samples in sewage, as health authorities said the disease may be spreading between “closely linked” individuals.
The UK Health Security Agency on Wednesday said it was investigating whether community transmission, or transmission between individuals without known links, was under way.
No polio cases have been identified and the HSA noted that the risk to public overall remained “extremely low”. If an outbreak is confirmed, the UK would lose the polio-free status it has held since 2003.
Polio, short for poliomyelitis, mostly affects children under the age of five, according to the World Health Organization. It can cause severe disease and paralysis in a small, but significant, subset of patients.
Health secretary Sajid Javid said on Wednesday that he was “not particularly worried” about polio after the virus was detected.
He told the BBC: “That’s because the UK Health Security Agency, what they have explained to me is that through routine testing of wastewater in north-east London, they have detected vaccine-derived polio virus.”
“And they are tentatively having an investigation to learn more about that,” he added.
The health agency said samples were taken from the London Beckton sewage plant, which has a catchment area of about 4mn people in north and east London, between February and May this year.
The HSA said the virus detected was vaccine-derived poliovirus type two, a type of virus that can live in the gut of people who have received a polio vaccine from overseas that is the shedded in wastewater.
Public health authorities on Wednesday urged parents to check their children’s vaccinations were up-to-date to ensure optimal protection.
The last UK case of wild polio, or polio not linked to vaccination, was recorded in 1984, the HSA said.
“Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower. On rare occasions it can cause paralysis in people who are not fully vaccinated,” said Vanessa Silba, a consultant epidemiologist at the agency.
“Most of the UK population will be protected from vaccination in childhood, but in some communities with low vaccine coverage, individuals may remain at risk.”
Vaccine-derived polio can sometimes appear in wastewater. The World Health Organization, for example, said last week that India, which has been polio-free since 2014, had detected one case of vaccine-related poliovirus in sewage in April. There is no suggestion the UK and India samples are related.
David Heymann, a professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine, said the discovery “reminds us that polio eradication has not yet been completed in the world”.
“The high vaccination coverage using inactivated polio vaccine in the UK will limit the spread of vaccine derived polio and protect those who have been vaccinated against polio paralysis,” he added.
Polio cases worldwide have decreased significantly in recent decades, thought remains endemic in Afghanistan and Pakistan as of 2020, according to the WHO.