Poliomyelitis: what is it and how is it spread?

By Smitha Mundasad and Philippa Roxby
health journalists

source of images, Getty Images

British health officials say they have detected the virus that causes polio in a worrying number of sewage samples in London.

There have been no recorded cases of people with the disease in the UK, but doctors are on alert.

What is poliomyelitis and how is it spread?

It can be a serious infection, caused by a virus that spreads easily through contact with an infected person’s feces (poo) or less commonly through droplets when they cough or sneeze.

It mainly affects children under the age of five.

The majority of people infected have no symptoms, but some feel like they have the flu with:

  • a high temperature
  • sore throat
  • headache
  • stomach pain
  • sore muscles
  • feel sick

A small number of infected people – between one in a thousand and one in a hundred – develop more serious problems where poliomyelitis invades the nervous system. This causes paralysis – usually of the legs.

It is normally not permanent and movement often returns gradually.

But it can be life-threatening – especially if the paralysis affects the muscles used for breathing.

At what age do you get vaccinated against poliomyelitis?

The UK previously used a highly effective oral polio vaccine in the form of drops. He switched to the new injectable form.

The NHS offers five doses from the age of 8 weeks to 14 years as part of routine childhood shots.

People must have all of these vaccines to be completely immune to the disease.

You can get vaccinated at any time if you have never had one before.

How can you protect children?

In the UK you can check your children’s red books to make sure they are up to date with their routine jabs. Contact your GP if you have forgotten one.

Health officials say the first three shots, given to young babies, provide good protection.

But take-up of the first three doses is around 86% in London, well below target levels, with the rest of the UK at over 92%.

This may be partly due to the fact that some populations in the capital move regularly, which makes it more difficult to access vaccines at the right time.

Figures for 2020/21 suggest some 34,000 five-year-olds in London had not received their fourth injection

Most of the UK population will be protected from childhood vaccination, but in some communities with low vaccination coverage individuals may remain at risk.

Is poliomyelitis a global problem?

The cases have reduced by more than 99% since 1988, rising from around 350,000 cases in more than 125 countries to 175 reported worldwide in 2019.

All continents except Asia have been certified polio-free.

The last recorded person to have contracted the wild virus in the UK was in 1984.

There are a few countries where the disease is still present – notably war-torn Afghanistan and Pakistan, where it has been difficult to vaccinate everyone.

Globally, 83% of infants had received three doses of polio vaccine in 2020, according to the World Health Organization.

Are there different types of polio?

Wild poliovirus is the best known form.

But there is another type, rarer, linked to the oral form of the vaccine.

The vaccine provides excellent protection against wild polio, is easy to use and has been deployed by many countries around the world, keeping millions of people safe.

However, it contains a weakened live form of the virus which can replicate harmlessly in the intestine. But this means that some of it is then excreted in the poo.

In rare cases, this weakened form can spread to unvaccinated people.

Over a long period, the vaccine-derived virus could change to look more like wild polio.

source of images, Getty Images

Many industrialized countries are now using the new injectable form which contains a killed version of the virus.

Both vaccines are safe and effective.

Over the past decade – a period in which more than 10 billion doses of oral polio vaccine have been administered worldwide – outbreaks of vaccine-derived poliovirus have resulted in fewer than 800 cases.

During the same period, in the absence of vaccination with oral polio vaccine, more than 6.5 million children would have been paralyzed by wild poliovirus.

Why is the poliomyelitis virus back?

A small number of polio virus samples are detected each year in the UK during sewage monitoring. However, this is the first time that a genetically related cluster has been found repeatedly over a period of months.

The polio virus detected in London most likely came from someone who had recently received an oral polio vaccine.

They will then have excreted the weakened vaccine virus in their stool.

It is likely that it was then passed on to another person at this point and has since infected others. However, none sought medical help.

How much of a problem is this?

The UK is taking the right approach so far, according to Sir Jeremy Farrar, director of the Wellcome Trust.

“It’s credit to the surveillance systems, it’s credit to the UK Health Security Agency for picking this up and then taking the right public health approaches.”

And Professor Paul Hunter, professor of medicine at UEA, said while the results were cause for concern, getting more people vaccinated would help stop the virus.

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