The Turnstone: talking about vaccines #28

Polio vaccination is still important (5 minute read)

Polio was one of the most feared diseases of the twentieth century. Now, it is almost eradicated, but it still remains a threat, even in countries where it hasn’t been seen in years. The USA, for example, recently had its first reported polio case in nearly a decade. Why does this disease still pop up where we least expect it to?

The short answer is – because not enough people are getting vaccinated. Even though polio seems almost forgotten in most countries of the world, it is still important that all children are vaccinated. But why, when polio is such a rare disease?

The answer to this question is not simple, but it is important. The story of polio vaccination illustrates some principles about how vaccines work, and can help us to have better conversations with those who are uncertain or hesitant about vaccination.

So, this month’s set of vaccine resources is aimed at helping you to understand the story of polio and polio vaccination.

Early depiction of polio, from Ancient Egypt (image credit: Fixi)

Polio – the disease

In the history of disease, the story of polio stands out as unusual. Many diseases declined, in wealthier countries at least, as public health measures such as sanitation were introduced. But at the end of the nineteenth century, polio, which hadn’t been considered a big problem, began to cause major outbreaks.

Polio is caused by a virus which is spread by contact with human waste. When sanitation was less effective, most babies came into contact with it while they were still being breast fed. If their mother had also been infected with polio, which most had, then immunity was passed through breast milk. Because of this immunity, the babies mostly suffered only a mild case.

But once sanitation improved, babies weren’t exposed when they were still being breast-fed. They caught the disease later, with no immunity, and were more likely to suffer a serious case of polio.

The following article is one of the best overviews I’ve read. It gives a good explanation of what polio is and why it emerged as such a problem in the 20th century (10 minute read).

Polio: a 20th century epidemic | Science Museum

A medical nightmare – and a miracle

In serious cases, polio damaged or destroyed nerve cells, resulting in temporary or permanent paralysis or death. In some cases, the breathing muscles were paralysed, leaving people unable to breathe and confined to “iron lungs”. These massive metal tanks, which encase the whole body except the head, breathed for polio patients when their bodies could not. When I first heard about iron lungs, they terrified me, but they were a medical miracle that saved many lives. Some people were only in an iron lung on a temporary basis, until they recovered their ability to breathe. But as of 2021, there were still a few people depending on them in the USA.

This is a long article and a little old (2017), but it is excellent. The author interviewed three remarkable polio survivors still dependent on iron lungs (18 minute read).

The Last of the Iron Lungs (gizmodo.com)

A tale of two vaccines

Two different polio vaccines were developed in the 1950s. Without both vaccines, it is unlikely that we would have been so successful in controlling polio. But each vaccine has crucial drawbacks which mean that we cannot yet consign polio to the history books.

The inactivated polio vaccine

Developed by Jonas Salk in the 1950s, the inactivated polio vaccine, contains polio virus which has been inactivated. It is given as a series of four injections over a period of at least 9 months or, more often, several years. It gives long-lasting protection against disease but doesn’t prevent someone from passing on the virus.

The oral polio vaccine

Developed by Albert Sabin, also in the 1950s, the oral polio vaccine contains live polio virus which has been weakened. As the name implies, it is given as drops by mouth, which makes it ideal for large-scale vaccination campaigns. When given as a series of three or more doses, it is extremely effective, even preventing transmission of the virus.

The following article explains more about the history of the two polio vaccines (6 minute read).

History of polio vaccination (who.int)

Vaccine shedding – it’s not a myth

If the oral vaccine is easier to administer and more effective than the inactivated vaccine, why is the inactivated vaccine still widely used? The answer is complicated but important. You may remember hearing, during the height of the Covid-19 vaccination campaign, completely false claims about “vaccine shedding” from people who opposed vaccines. There is no possible way that someone vaccinated with any of the Covid-19 vaccines can “shed” the virus or the vaccine. But with a live virus vaccine, and especially the oral polio vaccine, “shedding” can and does happen for a few weeks after someone is vaccinated.

So what does shedding of the oral polio vaccine mean? There’s good news and bad news. The good news is that unvaccinated people may “catch” the weakened virus from vaccinated people, and, as a result, end up getting vaccinated themselves. If there are a lot of unvaccinated people around, the weakened virus can keep on passing from person to person, vaccinating as it goes. This sounds like a good thing, but it’s not. As it spreads, the vaccine strain can mutate. In time, it can revert to a disease-causing form and then someone who is unvaccinated (or immune-compromised) can get a serious case of polio.

For this reason, once most people are immune to polio, countries start shifting to the inactivated polio vaccine, which can’t cause this problem. But in countries where there isn’t the infrastructure to support a vaccination campaign of an injected vaccine, the oral polio vaccine remains crucially important.

There’s a video here which explains how polio can result from vaccine strains of the virus (2 minute video).

Vaccine-Derived Polioviruses – GPEI (polioeradication.org)

Here’s a good article[1] about vaccine shedding, and why it cannot happen with Covid-19 vaccines, but it also talks about vaccines where shedding can happen, like the oral polio vaccine (7 minute read).

Vaccine Shedding: Facts, Myths, & More (healthline.com)

And finally, if all this talk about polio has motivated you to want to do something yourself, there are two organisations where you can donate to support the global campaign to eradicate polio.

Donate – GPEI (polioeradication.org)

---

[1] Note that Healthline.com has drawbacks in relation to some of its content, but in this case it gives a good explanation of the issues.