Public health officials have declared a national incident after routine surveillance of wastewater in north and east London found evidence of community transmission of poliovirus for the first time.
The UK Health Security Agency (UKHSA) said waste from the Beckton sewage treatment works in Newham tested positive for vaccine-derived poliovirus in February and that further positive samples had been detected since.
No cases of the disease or related paralysis have been reported, and the risk to the general public is considered low, but public health officials urged people to make sure that they and their families were up to date with polio vaccinations to reduce the risk of harm.
“Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower,” said Dr Vanessa Saliba, consultant epidemiologist at the UKHSA. “On rare occasions it can cause paralysis in people who are not fully vaccinated, so if you or your child are not up to date with your polio vaccinations it’s important you contact your GP to catch up or if unsure check your red book.”
“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,” she added.
Tests on UK sewage typically pick up a handful of unrelated polioviruses each year. These come from people who have been given the oral polio vaccine in another country and then travel to the UK. People given the oral vaccine can shed the weakened live virus used in the vaccine in their faeces for several weeks.
The London samples detected since February raised the alarm because they were related to one another and contained mutations that suggested the virus was evolving as it spreads from person to person.
The outbreak is believed to have been triggered by a person returning to the UK after having the oral polio vaccine and spreading it locally. It is unclear how much the virus has spread, but it may be confined to a single household or an extended family.
Poliovirus can spread through poor hand hygiene and contaminated food and water, or less often through coughs and sneezes. A common route of transmission is for people to get contaminated hands after using the toilet and then pass the virus on by touching food consumed by others.
While the UK generally has good uptake of the polio vaccine, with 95% of five-year-olds having had the jab, coverage lags behind in London, with only 91.2% of children vaccinated in that age bracket. In response to the detection of the virus, the NHS will contact parents of children who are not up to date with their polio vaccinations.
Most people who become infected with polio have no symptoms, but some develop a flu-like illness up to three weeks later. In between one in 100 and one in 1,000 infections, the virus attacks nerves in the spine and the base of the brain, which can lead to paralysis, most commonly in the legs. On rare occasions, the virus attacks muscles used for breathing, which can be fatal.
The UK switched from using the oral polio vaccine (OPV) to an inactivated polio vaccine (IPV), given by injection, in 2004. The shots are given in routine NHS childhood vaccinations at eight, 12 and 16 weeks as part of the 6-in-1 vaccine. Boosters are offered at the age of three and 14.
The UKHSA is now analysing samples of sewage from local areas that feed into the Beckton plant to narrow down where the virus is spreading. If those tests pinpoint the centre of the outbreak, public health teams may offer polio vaccination to those at risk.
Prof Nicholas Grassly, the head of the vaccine epidemiology research group at Imperial College London, said: “Polio is a disease that persists in some of the poorest parts of the world and the UK quite frequently detects importation of the virus during routine testing of sewage.
“In this case, there is concern that the virus may be circulating locally in London and could spread more widely. Fortunately, so far no one has developed symptoms of the disease, which only affects about 1 in 200 of those infected, but it is important that children are fully up-to-date with their polio vaccines. Until polio is eradicated globally we will continue to face this infectious disease threat.”