London celebrations

Polio: Should we be worried about the virus found in the sewers of London?

A microscopic view of poliovirus

Stocktrek Images, Inc./Alamy

Poliovirus has been detected in a number of sewage samples from London, prompting the UK Health Safety Agency (UKHSA) to urge anyone who is not up to date on their polio vaccines to get vaccinated.

The samples, detected at Beckton Wastewater Treatment Works between February and May, have so far been limited to sewage, with no human cases reported.

Nevertheless, it is expected that some degree of local transmission has taken place, with the virus having the potential to spread and cause serious illness, particularly among unvaccinated people.

What is poliomyelitis and how is it spread?

Poliomyelitis is a viral disease that mainly affects children less than 5 years old. It is usually spread by people not washing their hands properly after using the toilet and then contaminating food or drink that someone else has eaten. In rare cases, it can be spread by coughing and sneezing.

What are the symptoms?

Most people infected with poliomyelitis have no symptoms, but some develop flu-like symptoms such as high temperature and vomiting within a few weeks of infection.

In 1 in 100 to 1 in 1000 cases, the virus can attack the spinal nerves, causing paralysis. Poliomyelitis can also be deadly if it affects the nerves that control our respiratory muscles.

When was the last polio outbreak in the UK?

No cases of polio have been reported in the UK since 1984. The World Health Organization subsequently declared the UK polio-free in 2003.

Is it unusual to detect poliomyelitis in wastewater?

Wastewater samples are routinely tested in the UK for poliovirus and other pathogens, such as norovirus and hepatitis A and E.

One to three “vaccine-like” polioviruses are detected each year. These were previously one-off findings that occurred after a person received a live oral polio vaccine and passed the virus in their stool. These oral vaccines are not given in the UK.

In Beckton’s samples, several closely related polioviruses were identified.

“It is likely that there has been some spread between closely related individuals in north and east London and they are now shedding the poliovirus type 2 strain in their faeces,” according to the UKHSA. .

This strain could cause infection, but probably not serious illness, in people who received the injected polio vaccine. Used in the UK, it contains a “killed” version of the virus.

How can people shed poliovirus in their stool?

Live oral polio vaccines have not been used in the UK since 2004, but are administered in areas of the world that are actively fighting infection, such as Afghanistan and Pakistan. Unlike vaccines given by injection, oral vaccines are relatively inexpensive and easy to administer.

The main disadvantage oral vaccine is that it can lead to vaccine-derived poliovirus in poorly immunized populations. This vaccine works by giving a weakened version of live poliovirus. This causes infection, but has been modified to not cause serious illness except in rare cases. The virus then replicates in the intestine, which can lead to its excretion via the faeces.

As for the sewage samples from Beckton, the strain found was likely introduced by someone who traveled to the UK after recently receiving the live oral vaccine.

What makes it different from previous polio detections in sewage?

Previous detections of poliovirus in sewage samples have occurred independently as separate cases.

In Beckton’s samples, the viruses were identified over a period of four months. They are also closely related to each other and contain mutations that suggest they are evolving.

According to David Salisbury of the World Health Organization’s Global Commission for the Certification of Poliomyelitis Eradication, these mutations “imply that it has circulated among individuals, possibly including those who have been vaccinated with the vaccine. inactivated poliomyelitis”.

This circulation may have occurred in the country where the person received the live oral vaccine or possibly in the UK, but without causing symptoms.

Although no human cases have been reported so far in the UK, Kathleen O’Reilly at the London School of Hygiene & Tropical Medicine expects local transmission to have occurred undetected.

“With the sewage samples, genetic analysis indicates multiple chains of transmission, suggesting that some people are spreading to each other,” she says. “People who have never been vaccinated have a much higher chance of getting the infection and shedding it for a long time.”

Are only unvaccinated people at risk?

The risk of serious illness from polio is low in the UK, according to the UKHSA. “Most of the UK population will be protected from childhood vaccination, but in some communities with low vaccination coverage individuals may remain at risk,” Vanessa Saliba to UKHSA said in a statement.

In the UK, an injected vaccine is given to babies three times before turning 1. Two other booster shots are then administered before the age of 15.

More … than 92 percent of the UK population has received at least three doses of polio vaccine, but take-up is lower in London, at around 86%.

“In populations with low immunization rates, it is possible for live polio vaccine to spread from person to person,” said Paul Hunter at the University of East Anglia, UK, in a statement to the Science Media Centre.

Overall, how concerned should we be?

“There have been no paralytic cases so far,” Hunter said. “So at this time there is unlikely to be an immediate risk to public health, but if such transmission continues, the risk is that the virus will eventually evolve into a virus that causes paralysis.

“If this happens, it could pose a serious risk to people who have not been vaccinated. These vaccine-derived transmission events are well-described and eventually die out without causing harm, but this depends on improving vaccine coverage.

Jonathan Ball at the University of Nottingham in the UK, said the threat of disease in the country is “low” due to our relatively widespread use of the injected vaccine, “but we could see continued spread of the vaccine strain as the Killed vaccine does not always protect against infection”.

“Ultimately, however, this virus should go away due to the high levels of vaccination here,” he told the Science Media Center.

The NHS will contact parents of children under 5 in London who are not up to date with their polio vaccinations, urging them to get vaccinated.

Learn more about these topics: