Polio is an infectious disease that has now been eliminated in most of the world. It’s endemic only in Afghanistan and Pakistan, with low numbers of “breakthrough” cases in some other places as a result of the vaccine technology used there. In the first half of the twentieth century, polio was not only widespread in the Western world but widely feared, as outbreaks left in their wake a large number of kids left paralysed permanently after their bodies cleared the infection, a condition known more properly as post-polio syndrome.

Similarly to the modern era’s Covid-19, the vast majority of those infected with poliovirus did not die or go on to develop the devastating post-polio syndrome – it was feared not because the outcomes were horrific for most of those afflicted, but because they could be so horrific even if for a small minority. According to this tweet(external link):

  • 72% of people infected with polio virus do not have any outwardly visible symptoms
  • approx. 25% have mild flu-like symptoms like fever, tiredness, muscle pain, sore throat, headaches and nausea
  • a small number develop more serious symptoms that indicate damage to the brain or spinal cord:
    • some number (?) get paresthesia, a “pins and needles” sensation in the legs
    • about 4% develop meningitis, which is an infection of the protective covering over the brain and spinal cord
    • 0.5% develop paralysis. Of those who develop paralysis, up to 10% die as the muscles that make them breathe can get paralysed.

I’ve seen the comparison made between post-polio syndrome and Long Covid, mostly to make the argument that we should be taking the risk of Long Covid more seriously.

In 2022, polio has been detected in the wastewater of London and New York City (meaning at least someone in both those cities has polio). It’s thought that this is likely the result of someone who had a “breakthrough” infection travelling to these cities and infecting unvaccinated people there.

Basically, there are two types of polio vaccines. The type usually used in the West doesn’t have any risk of “breakthrough” infections, but it’s much more finnicky to store and transport. The type used in many part of the developing world uses live but heavily weakened virus, and is used because this is much easier to transport and store in places that may only have intermittent access to electricity, etc. Breakthrough infections are rare, but can occur especially in children with suppressed immune systems, and those with breakthrough infections can pass their infection on to other people (which is what’s happened in London and NYC).

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