ok this was gonna be a small tag rant but then it got way too long.
While I do not want to minimize the amazing step forward in healthcare Edward Jenner made, I have a nitpick with the way it's framed. I don't blame OP bc I do NOT think it was intentional, it's a fun science education blog providing cool rebloggable information, but if you don't know better already it seems as though first there was smallpox and nothing we could do about it and then Edward Jenner was the first to discover that cowpox provided immunity to smallpox and provided the first way of preventing smallpox infections. And that's... very untrue.
So back to at least the 1500s, multiple countries and cultures in Asia, Africa, and the Middle East practiced something called variolation to inoculate against smallpox. They would take either powdered smallpox scabs or the liquid from a smallpox pustule and rub or insert it into a small scrape or incision in a person's arm. They would (generally speaking) get a much milder, usually localized case of smallpox, recover, and then have immunity to smallpox going forward. Only about 1-2% of people who received variolation died from it, which is much better than what I believe was a 30% death rate for full-blown smallpox.
So knowledge about this had apparently spread to Europe (or was independently discovered at least) by at least 1600 because as far back as that there was at least one town in Wales that practiced it, but by the 1700s in Europe and the American colonies it wasn't really a thing that was practiced. As far as I can remember it was largely considered barbaric or unsafe.
And then in 1717 in Constantinople the wife of the British ambassador to the Ottoman Empire, Lady Mary Wortley Montagu, got to witness the practice of variolation. Lady Mary had survived smallpox a few years prior, and lost her brother to it shortly before, and had a small child that she did not want to have to suffer it, so after learning about it and about how smallpox was so rare among the Turks who practiced it, she had her 5-year-old son variolated in 1918, and when she returned to England in 1721 she was a passionate advocate for the practice.
Now of course the problem with inoculating against smallpox by inducing a weaker case of smallpox is that it's still smallpox. While usually the infection was localized, rather than spreading from the respiratory system to the lymphatic system and from there to the whole body like regular cases of smallpox, it was still infections and could spread smallpox to others. Which is how we come to cowpox.
Cowpox was a disease that was much less severe than smallpox. It was not deadly, it produced large painful sores yes but usually only on the hands and sometimes the neck, and it was not airbone - you had to get fluids directly into a cut or a mucus membrane to contract it. By the late 1700s it was already known by a number of authorities that people who worked a lot with cows and horses (the latter probably due to horsepox apparently?) were less likely to get smallpox. (The British government did a study or something at one point and had found that infantry members were less likely to get smallpox than other members of the military, probably bc of the horsepox. I have no more info on what this was supposed to be studying I just know it happened)
There were at least 5 or 6 people who'd had contact with cowpox in that period who tested the theory that getting cowpox could give you immunity to smallpox, including an English farmer who inoculated his wife and kids when a smallpox epidemic was sweeping through their area and none of them got it, and a German teacher named Peter Plett who successfully used cowpox to inoculate the children he was tutoring, but when he reported it to the local medical university they kind of ignored him because they were still favoring variolation and were apparently uninclined to change.
Edward Jenner's main contribution when he did his experiments in 1796 was that he inoculated a number of people with cowpox, then he came back and essentially variolated them at multiple later dates with smallpox variolation material and they showed no symptoms, and then people listened to him. There's some other specifics about how the inoculation/vaccination could be passed from person to person and didn't need to be directly from a cow too, but like the big one was he proved that cowpox could provide immunity to smallpox in a way none of the other attempts had done (by intentionally introducing smallpox to inoculated subjects and getting no illness).
NONE OF THIS IS SAID TO MINIMIZE WHAT HE DEVELOPED. Like holy shit it really was game-changing to have that evidence and after that he also helped develop ways of creating and disseminating the vaccine so you didn't have to have a sick cow handy to be inoculated. It was huge and it WAS absolutely a game-changer.
But he stood on the shoulders of the work, knowledge, and treatment that came before him. This is not a bad thing! Every advancement in science and medicine and technology does this. But it is worth noting that there was a lot of work and a lot of people before him that got the world and its knowledge to the point where he could change the game so thoroughly.
If Lady Mary hadn't campaigned so hard for variolation AND put her money where her mouth was by variolating her own children, Jenner might not have thought to experiment with the process. Heck, he may've died of smallpox for all we know, since he was variolated as a child. If others hadn't been experimenting with cowpox infections as a way to provide smallpox immunity in the 1770s and 1780s maybe he wouldn't have even known about the connection between cowpox and smallpox to form the idea for his experiment.
In the late 1700s smallpox was one of history's most deadly diseases, despite advances in medicine and inoculation. In 1796, a surgeon and doctor named Edward Jenner learned about an under-explored phenomenon where individuals who contracted or were inoculated with cowpox appeared to be immune to smallpox.
Jenner tested this by infecting multiple people with cowpox, who got mildly ill and subsequently showed no symptoms when directly exposed to smallpox even on multiple occasions.
His results laid the foundation for the future of immunology and vaccination, and as a result smallpox was entirely eradicated in 1980, the only disease to be completely wiped out.
