Polio is spreading in Britain for the first time in nearly 40 years, health officials have warned, as they declared a national incident, and urged people to make sure they are vaccinated.
Britain was proclaimed polio-free in 2003 with the last wild case detected in 1984, making the new outbreak the first transmission event since the 1980s.
The UK Health and Security Agency (UKHSA) said that a polio virus had been detected in sewage from North and East London in February.
Although this would not normally be a concern, a mutated version of the same strain was picked up again in April and May, suggesting there has been ongoing spread between individuals over several months, which has allowed the virus to evolve.
Health experts are also concerned that doctors no longer recognise the symptoms of polio as it has not been circulating for decades meaning cases could have been misdiagnosed. GPs are being asked to look out for, and report, any signs of the virus.
The virus was originally shed from an individual who was vaccinated with a live virus abroad, but has since mutated into a type more like wild polio, which, on rare occasions, can infect the spinal cord and base of the brain, causing paralysis and breathing problems.
Lower vaccine uptake in London
So far, there have been no reported cases of polio, and health experts say the risk is low for children and adults who had had three doses of vaccine, but urged unvaccinated individuals to come forward for jabs and boosters.
Dr David Elliman, a consultant paediatrician at Great Ormond Street Hospital, said: “Although the uptake of polio vaccines is high in the UK, there are children who are unimmunised and therefore at risk of developing polio if in contact with this virus.
“The risk is small, but it is easily preventable by the vaccine.”
Children are routinely vaccinated against polio, but north London has some of the worst uptake rates in the country, with around one third of youngsters in Hackney and the City of London failing to have a first jab at 12 months, and nearly one quarter missing a shot at 24 months.
Coverage across the capital for three doses was below 85 per cent in eight out of 33 London local authorities in the 2020/2021 academic year, and around one third of children have not had a pre-school or teen booster.
A recent report by the UKHSA also found that in Hillingdon in West London, just 35 per cent of teenagers had been boosted against polio, the worst uptake in the country.
Dr Vanessa Saliba, Consultant Epidemiologist at UKHSA 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 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.”
Virus can lead to paralysis
Health experts believe the virus was probably imported from an individual who had recently been given an oral polio vaccine abroad, possibly in countries such as Nigeria, Pakistan or Afghanistan where outbreaks are still common.
Oral vaccines contain three live strains which can be shed and enter the sewage system.
In unvaccinated populations, between 1 in 100 and 1 in 1,000 polio infections can lead to paralysis, and officials are concerned that even fully vaccinated people could catch and spread the virus without realising.
The virus was picked up during routine fortnightly monitoring of sewage at London Beckton Sewage Treatment Works, which covers four million people, and more localised testing is now taking place in six other areas in the capital to try and pinpoint the outbreak.
The UKHSA said that if a specific area was found they may target it with a mass vaccination programme to make sure communities are protected.
Jane Clegg, chief nurse for the NHS in London said: “The majority of Londoners are fully protected against polio and won’t need to take any further action, but the NHS will begin reaching out to parents of children aged under five in London who are not up-to-date with their polio vaccinations to invite them to get protected.
“Meanwhile, parents can also check their child’s vaccination status in their Red Book and people should contact their GP practice to book a vaccination should they or their child not be fully up-to-date.”
Britain's history with polio
Britain began vaccinating against polio in 1955, and moved to a live oral vaccine in 1961, which allowed the virus to grow in the human gut, offering almost complete protection.
While polio was still spreading in the community the live vaccine was considered preferable specifically because the virus could pass from person to person, enhancing immunity and ensuring people picked it up when young when they were less likely to be paralysed.
But after the eradication of polio, Britain moved to an injectable inactivated vaccine in 2004, which does not shed into the sewage system, stopping spread.
Prof Paul Hunter, professor in medicine at UEA, said: “In populations with low vaccine uptake it is possible that the live polio vaccine can spread from one person to another.
“If this is sustained, over time (one or two years) this vaccine derived virus can mutate to become fully virulent again and can start to cause paralysis in people who have not been vaccinated.
“Vaccine derived transmission events are well described and most ultimately fizzle out without causing any harm but that depends on vaccination coverage being improved.”