Gym Infections Causes, Treatment, and Prevention
Polio: What Is It And How Does It Spread?
By Smitha Mundasad and Philippa RoxbyHealth reporters
The virus that causes polio has been found in a concerning number of sewage samples in London and all children aged one to nine years old are to be offered a polio booster jab.
There have been no confirmed cases of people becoming ill with the disease in the UK, but health officials want to ensure children in London are completely protected.
What is polio and how does it spread?It can be a serious infection, caused by a virus which spreads easily through contact with the faeces (poo) of an infected person or less commonly through droplets when they cough or sneeze.
It mostly affects children under five years old.
The majority of people with the infection have no symptoms but some feel like they have the flu with:
A small number of infected people - between one in a thousand and one in a hundred - develop more serious problems where polio invades the nervous system. This causes paralysis, usually of the legs.
This is not normally permanent and movement often comes back gradually.
But it can be life-threatening - particularly if paralysis affects muscles used for breathing.
What age do you get the polio vaccine?The UK used to use a highly effective oral polio vaccine that came as drops. It has switched to the newer, injectable form.
The NHS offers five doses from the ages of 8 weeks to 14 years as part of routine childhood jabs.
People need to have all five doses of the vaccination to be fully immunised against the disease.
How are children being protected?Parents and carers of nearly one million children in Greater London will be contacted by their GP within the next month so they can get another polio vaccine, called a booster.
Experts say this will act as an extra precaution to stop polio spreading, even for children who are already up to date with their vaccines.
The NHS in London is contacting contact parents when it's their child's turn to come forward.
Parents are urged to take up the offer of the top-up dose - whether it's a booster or a catch-up one they had missed - as soon as possible.
This is to make sure they have a high level of protection from paralysis.
How many children have been vaccinated?Take-up of the first three doses is about 86% in London, well below target levels, with the rest of the UK at over 92%.
This may in part be down to some populations in the capital moving regularly, making it harder to access vaccines at the right time.
Figures for 2020/21 suggest some 34,000 children aged five in London had not received their fourth dose out of five.
Is polio a problem worldwide?Cases have decreased by more than 99% since 1988, from an estimated 350,000 cases in more than 125 countries then to 175 reported globally in 2019.
All continents, except Asia, have been certified as polio free.
The last person recorded to have acquired the wild virus in the UK was in 1984.
There are a few countries where the disease is still found - it includes 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 kinds of polio?Wild poliovirus is the most commonly known form.
But there is another type linked to the oral form of the vaccine.
The vaccine offers 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 gut. But that means some is then excreted in poo.
In rare cases, this weakened form can spread to unvaccinated people.
Over a long period the vaccine-derived virus might change to become more like wild polio.
Many industrialised countries now use the newer injectable form which contains a killed version of the virus.
Both vaccines are safe and effective.
In the last decade - a period during which more than 10 billion doses of oral polio vaccine were given worldwide - vaccine-derived-polio virus outbreaks resulted in fewer than 800 cases.
In the same period, in the absence of vaccination with the oral polio vaccine, more than 6.5 million children would have been paralysed by wild poliovirus.
Why is the polio virus back?A tiny number of samples of the polio virus are detected each year in the UK during sewage surveillance. However, this is the first time that a genetically-linked 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 shed the weakened vaccine virus in their stools.
It is likely it was then passed on to another person at this point and has since infected some others. None have sought medical help though.
Similar traces of the virus, which could be linked, have also been found in sewage in Jerusalem, in Israel, and in New York state in the United States.
How much of a problem is it?The UK is so far taking the right approach, according to Sir Jeremy Farrar, director of the Wellcome Trust.
"It's a credit to the surveillance systems, it's a credit UK Health Security Agency for picking this up and then taking the right public health approaches."
And Prof Paul Hunter, professor of medicine at UEA, said getting more people vaccinated would help stop the virus.
Graphics by Visual Journalism Team
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Live Oral Polio Vaccine Proved Safe And Effective
A version of this article appears in the May 28, 1960 issue of Science News.
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From the Nature Index Paid Content
Super-engineered Vaccines Created To Help End Polio
By James Gallagher
Health and science correspondent
Scientists have "super-engineered" polio vaccines to prevent them mutating into a dangerous form that can cause outbreaks and paralysis.
The oral vaccines contain weakened live polio viruses and the genetic redesign locks them into that weakened state.
The US and UK teams have now created upgraded vaccines against all three types of polio.
However, better vaccines still need to reach every child in order to stop the disease.
Polio can spread into the nervous system, causing paralysis. Cases have fallen by more than 99% since the late 1980s and about 20 million people who would have been paralysed can walk thanks to vaccines.
The original or "wild" poliovirus is now contained to small pockets of Afghanistan and Pakistan and the oral vaccines play a pivotal role in the attempt to rid the world of polio.
"The issue is they're genetically unstable," Dr Andrew Macadam, from the UK's MHRA, told BBC News.
It takes only one mutation to turn the safe polio vaccine back into a virus that can move out of a child's stomach, invade their nervous system and cause paralysis.
And if those viruses spread from an immunised child - through their contaminated faeces - there is a risk of infecting the unvaccinated and triggering an outbreak.
There are now more cases of "vaccine-derived polio" than of the wild poliovirus and the polio detected in London's sewers last year was connected to the oral vaccine.
So the researchers have genetically altered the weakened virus even further to make it much harder for it to start causing paralysis again.
"By genetically modifying this part of the virus, we could modify this region so it couldn't revert and this I think has been remarkably successful," Dr Macadam said.
Prof Raul Andino, from University of California San Francisco, said he was "super-proud" of the scientific effort showing the vaccine was "50 to 100 times more stable".
Image source, Getty Images Image caption,A man in an iron lung, to keep him breathing after polio paralyses the chest muscles
In March 2021, the World Health Organization made the researchers' vaccine against type-two polio available for emergency use. Since then, it has been used more than 650 million times.
Now, in the journal Nature, the researchers have detailed the creation of stable vaccines against polio types one and three.
The first-stage human trials of the upgraded vaccines have already been conducted - and, the researchers say, the data, which is still being analysed, is "very promising".
The trio represent the first new polio vaccines in 50 years.
"I don't think there's any question that they're helpful, the new vaccines address the instability question, but it doesn't address the coverage issue," Dr Macadam said.
'Impressive science'
Tackling the last 1% of polio cases has proven stubborn. The original goal was to completely eradicate polio by the year 2000 - but delivering vaccines to some of the poorest and most conflict-ridden parts of the world has been a challenge.
Prof Alan Barrett, from the Sealy Institute for Vaccine Sciences, at the University of Texas, called the "super-engineered" vaccines a feat of "impressive science".
"[But] will it lead the endgame to the finish line? That is a big question," he added.
Joseph Swan, from the World Health Organization and the Global Polio Eradication Initiative, said more stable vaccines were a "significant part" of the plan for a polio-free world.
But, he said: "Simply having these new and better tools will not get us over the finish line - vaccination, not just vaccines, is what will end polio."
There was now a "unique opportunity" to eradicate wild poliovirus - but vaccine-derived polio outbreaks were causing problems in places facing "complex humanitarian emergencies", in the Democratic Republic of Congo and Yemen.
The oral polio vaccine is no longer used in the UK and other countries with established healthcare systems as they have moved to the polio injection.
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