Polio might seem like a disease of the past, but James Gallagher* says that until it is eliminated in the two remaining countries where it’s endemic, it remains a threat to us all.
Polio used to be one of the most feared childhood diseases. It can attack the nervous system and, in just a few hours, leave someone paralysed.
If it paralyses the chest muscles, people are unable to breathe and the sarcophagus-like iron lung, which uses bellows to keep the patient breathing, was once a common sight on polio wards.
All this feels like a long-forgotten era — and for good reason. The disease has almost been wiped off the face of the planet.
The United Kingdom’s last case of natural polio was in 1984.
This is the context in which to consider the news polio has paralysed a young man in the United States and, in London, a million children are being urgently immunised.
Since they were developed in the early 1950s vaccines have completely transformed polio.
Without them, 20 million people who can walk today would have been paralysed, the World Health Organisation estimates.
The disease has been beaten back from a global problem in the 1980s to enclaves in just a couple of countries now.
This includes the outstanding triumph of Africa being declared polio-free in 2020.
While Afghanistan and Pakistan are the only countries where polio continues to circulate, this endemic disease remains a threat to the rest of the world.
First, these countries can seed outbreaks elsewhere.
The first case of wild polio in Africa for more than five years was reported in a three-year-old girl in Malawi.
It was the same strain found in Pakistan, although nobody is sure how it travelled.
In February, Malawi had to declare a wild polio outbreak.
Secondly, the vaccine used both in endemic countries and to deal with outbreaks can itself create a problem.
This is what is now affecting the UK and other countries.
The most potent polio vaccine uses oral drops of a weakened but still live form of poliovirus.
It is cheap, easy to give and leads to outstanding immunity, which makes it ideal for responding to outbreaks.
However, it works by causing a stomach infection, so it is in people’s faeces, from where it can spread to others.
At one level, this is advantageous as it indirectly immunises others, but as it passes from one person to the next, it can mutate until it can cause paralysis again, known as vaccine-derived poliovirus.
This ability to revert to its more dangerous form is why countries aim to switch to an injection of dead virus once they are polio-free.
The UK has used injections since 2004, so what is now turning up in London sewers is a virus that has come from using the oral vaccine elsewhere in the world.
Some of the samples show signs of regaining the ability to cause paralysis — and genetic analysis suggests the virus has been spreading.
It is also directly related to samples found in wastewater in the US and Israel.
For the fully vaccinated, the risks are negligible, but the risk of paralysis for the unvaccinated is between one in 100 and one in 1,000, depending on their age.
Overall, the UK has high rates of vaccination, but there are pockets where far too few have had the vaccine.
Across London, 15 per cent do not receive the three doses of vaccine in their first year of life. In some boroughs, that rises to nearly 40 per cent.
These low rates are one possible explanation why the virus is spreading.
Polio feels like a disease of the past, but the virus being found in London and the case of paralysis in the US are a particularly loud wake-up call to Governments that we cannot be complacent about polio.
Scientific developments should make a difference — a new, more stable version of the oral vaccine is less likely to revert back to causing paralysis, for example.
Ultimately, polio needs to be tackled in the two remaining endemic countries —otherwise the threat of outbreaks will always be there.
That is a challenge not just about science or money but also of politics and society.
The US was criticised for damaging efforts to defeat polio when it used a fake vaccine program to try to find former al-Qaeda leader, Osama Bin Laden.
We are so close to the end of polio, but we have been close for a long time.
The disease is a diminished threat, but it will not be over until it is over everywhere.
*James Gallagher is the Health and Science Correspondent for the British Broadcasting Corporation. He can be contacted on Twitter @JamesTGallagher
This article first appeared on the BBC Health News website.
