Polio: everything is super weird

 So, I stopped reading Yuletide stories after that last post, which is not because I feel done reading Yuletide stories, so much as because I started reading articles about polio epidemiology. And that was kind of expectedly fascinating, and now I'm writing about it in multiple contexts in my life, so why not here also? 

I started reading this stuff for a couple of school-related reasons, one being that I have, for bureaucratic reasons, to write a research paper and have totally free choice on the topic, and the other being that I took multiple courses last semester that said something about the history of the physical therapy profession like "Physical therapy in the U.S. formed as a profession due to World War I and the polio epidemics of the early 20th century," and then moved on to, like, giving all the names that the American Physical Therapy Association has ever had, like those two pieces of information were equally interesting. Which they were not! 

Anyway, through this process I realized that I knew about polio as a Success Of Vaccination, and a Disease FDR Once Had That Led To Paralysis, but like... nothing else. NOTHING ELSE AT ALL. For example, if physical therapy was needed to treat the patients of the polio epidemics of the early 20th century, why was it not also needed to treat patients from polio epidemics that occurred before that?

Anyway, here are some weird facts about polio. 

1. There apparently just weren't major epidemics of polio before the late 19th or early 20th century. Individual cases are recorded as early as the 18th dynasty of ancient Egypt, and outbreaks start being recorded in the early 19th century, but the early-mid 20th century seems to be unique as a time period when there were regular, major epidemics.
2. This is because prior to the 19th or 20th centuries, basically everyone just always got all three strains of poliovirus in the first few years of their life; epidemics were a result of improved sanitation allowing a buildup of unexposed individuals who could all get infected at once. They started happening in countries all over the world as development progressed in the 20th century.
3. But if everyone used to always get polio, why didn't everyone have lower limb weakness or paralysis? Turns out, polio is a virus that primarily colonizes the digestive system and is usually (in about 75% of cases) completely asymptomatic. Under 1% of cases lead to the paralysis you think of when you think of polio.
4. The low incidence of characteristic symptoms and poor reporting led to a belief that the burden of polio was much lower in pre-epidemic time periods and areas than it really was; until a series of surveys was conducted the 1970s, public health goals were to control polio in epidemic areas and prevent it from becoming epidemic elsewhere, even though incidence rates overall were about as high where it wasn't epidemic yet as they had been in the epidemic era in the U.S.
5. Obviously this was all super confusing in the time period when epidemics were beginning to arise; people had some great/terrible theories about what could be responsible for the spread of this disease (because, as it was hitting clean suburbs as hard or harder than dirty tenements, it didn't fit well into contemporary models of disease). For example: poisonous caterpillars, electric radio waves, fumes from the subway. Also, of course, plenty of people were eager to blame immigrants and the poor despite the evidence not supporting that conclusion. 
6. There are basically two polio vaccines, an injected vaccine using inactivated virus (can't make you sick), and an oral vaccine using live attenuated virus (can make you sick—the attenuation of the virus lessens this risk). This is basically the same situations as with flu vaccines, except that the live attenuated vaccine for the flu is a nasal spray. Early on there were scholarly arguments as to whether the oral vaccine caused cases of paralytic polio that seemed to be associated with vaccination. Now it's known that it does; over half of cases of paralytic polio reported in the first part of 2018 were associated with the oral vaccine, rather than wild poliovirus. But this situation is only possible because the oral vaccine has been used so successfully against the wild virus—unlike the injected vaccine, it's been shown to confer immunity to untreated contacts of vaccinated individuals, because it is a highly contagious live virus. It's very unlikely that polio eradication could have been successful so quickly in so much of the world with only the injected vaccine available. 

In summary: polio is super weird and now I kind of want to read polio researcher RPF. There are a lot of great fights/rivalries in the literature; I think it could work.  If you want to read more, I'd start with this paper, although if you are specifically looking to read about Science Rivalry and don't mind reading about people injecting viruses into monkeys, this one is much more focused on that.