And the virus evolved to be less deadly and people evolved to have better immune responses to it.
The "Spanish Flu" still exists, and is all around us. Endemic to humanity. Meaning the H1N1-subtype of the influenza virus. Which killed 50-100 million people in 1918-1920. (Nowadays it's called the seasonal flu)
I'd like to find an image of anti-antivaxxers, from around that time. They had some good burns against the silly antivaxxers and I just can't remember what they were.