Thread by @Gurdur

1/ Going to slowly do a set of threads on the history of #polio itself, & then on the #PolioVaccines. This is for various concepts, including endemicity, epidemicity, risk calculation, & so on. Polio is an ancient disease. Here's a 3,400-year-old depiction thought to be b/c polio

2/ The first really important point is that polio has been around as long as humans have written, and it has been *everywhere* where humans are, in the New World AND the Old World before the Columbian Exchange, *everywhere* with humans.

3/ The next really important point is that polio epidemics — waves — were practically unknown before the 20th century. Yet polio itself was known & described before the 20th century. So what happened, why the big change? Why epidemicity, rather than... endemicity?

4/ To begin to understand, we need to look at the polio virus more. It's a tiny virus, the smallest significant virus known; most likely evolved from a Coxsackie A virus ancestor, thousands of years ago, very distantly related to common-cold rhinoviruses.

https://twitter.com/Gurdur/status/1473924058030956545

5/ Different viruses, even if related, do different things. Your average Coxsackie A virus doesn't usually do much; every now & then it causes hand, foot and mouth disease in humans, though there's a rare strain that can cause a polio-like condition. There's another difference...

6/ Polio evolved off a Coxsackie A virus thousands of years ago, & is related to rhinoviruses. Your average rhinovirus spreads by disgusting people sneezing all over you, & whoops you have the common-cold. Coxsackie can do sneezes, but does water maybe mostly. Polio does water.

7/ Polio, unlike its cousins, doesn't make you sneeze usually. It really likes being in water, so transmission is usually via water, & since it's a human-only virus, what it rly needs is sewage-contaminated water. If it gets all that, it just hangs around with humans, forever.

8/ IOW, prior to the 20th century #polio was ➡️ #endemic. That is, transmission was roughly R0=1. Humans would normally get immune after a bout, so it survived in large human groups *everywhere*, on an eternal merry-go-round, steady-state, always in the background, never in waves

9/ Prior to say 1890, #polio was usually noticed, if at all, in infants ½~4 years old. For most, it was a mild fever, but always it was noticed that a few would have paralysed limbs, with withering, needing crutches. A constant in history. Some, esp. older, would've rly bad luck

10/ The usual picture of a child, sometimes an adult, with a withered leg or arm, was known to everyone everywhere. Alan Alda, Mia Farrow, Donald Sutherland, Johnny Weissmuller, Francis Ford Coppola, Ian Dury (see below), all survivors of bad polio bouts

11/11 New thread, linked below. Before we explore why polio changed from endemic to epidemic, and the vaccines history, let's look at what typical antivaxxers or denialists would make of it if it all happened today, instead of around 1955.

https://twitter.com/Gurdur/status/1474007225035333644