Polio alert: why a national incident has been declared

A national incident has been declared as polio is spreading in the UK for the first time in nearly 40 years.

The UK Health Security Agency (UKHSA) said that waste from sewage treatment works in Beckton, east London tested positive for the polio virus in February, with further positive samples detected since.

Analysis of UK sewage normally shows up a few polioviruses each year, but the London samples detected since February “raised the alarm” because they are “related to one another and contained mutations that suggested the virus was evolving as it spreads from person to person”, reported The Guardian.

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The outbreak is believed to have been triggered by someone returning to the UK after having been vaccinated with a live virus abroad, which then mutated into a type of polio “more like wild polio”, said The Telegraph.

Britain was declared polio-free in 2003, and the “last wild case” of polio was detected in 1984, so this new outbreak is the “first new transmission event since the 1980s”, added the paper.

What is the risk to the public?

Officials believe that the spread is probably between “two closely linked individuals”, most likely “extended family members” who are now shedding the polio virus strain in their faeces, reported Sky News.

Urgent investigations will now try to establish the extent of any community transmission and identify where it might be happening.

However, health experts at the UKHSA have said that this type of vaccine-derived poliovirus is “rare” and the overall risk to the public is “extremely low”.

So far the virus has only been detected in sewage samples and no cases of the disease or related symptoms, such as paralysis, have been reported. Public health officials are urging people to make sure they and their families are up to date with their polio vaccinations to reduce the risk of harm.

“Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower,” Dr Vanessa Saliba, a consultant epidemiologist at the UKHSA, told the broadcaster.

“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.”

Children in the UK are routinely vaccinated against polio, but the area of London where the samples of poliovirus were found has “some of the worst uptake rates in the country”, said The Telegraph. The paper reported that “one third of youngsters” in Hackney and the City of London have not had their first jab at 12 months, while “nearly one quarter” is missing a second shot at 24 months.

And coverage across the capital for the full three doses of the vaccine has dropped below “85% in eight out of 33 London local authorities in the 2020/2021 academic year”, added the paper.

What are the symptoms and how is it spread?

Polio can spread through “poor hand hygiene and contaminated food and water, or less often through coughs and sneezes”, said The Guardian. One 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”, said the paper.

Most people who have become infected with polio have no symptoms, but some can develop a “flu-like” illness up to three weeks later. And “in between one in 100 and one in 1,000 infections” the virus can attack nerves in the spine and base of the brain, “which can lead to paralysis, most commonly in the legs”. On rare occasions, becoming infected with the illness can lead to death if the virus “attacks muscles used for breathing”.

What next?

If more virus samples are identified in the coming weeks, then the emergency could be “scaled up”, which would mean targeted interventions such as “small batch vaccinations and the collection of stool samples from areas where the polio virus has been found”, said Sky News.

Speaking to the broadcaster, Professor Adam Finn, a member of the Joint Committee on Vaccination and Immunisation (JCVI), said that further samples are likely to be found.

“I’m afraid there is reason to suggest it spread because this has been picked up now over a period of several months,” he said. “And when we see importations that are like a one off, if you like, somebody who’s recently been vaccinated, that usually just pops up for a short time and then disappears, whereas we’re seeing genetically related viruses persistently over a period of months now.

“And that strongly suggests that there’s transmission going on between people within the UK and in this area of London in particular.”