I'm no viral infection expert, but from what I read in that book viruses are, excuse my language, some scary ****! The spikes you see on the virus are important in that they mechanically fit and attach to a human lung cell. Like velcro. It takes a day or two but once it penetrates the cell's wall it's on. The cell is doomed.
It immediately replicates in enormous numbers but because it's fairly low form of life only about 10% will be exact copies that will velcro on to another human lung cell. That's enough to be a problem, but it's the other 90% that gets scary. It's a mutant swarm that can morph into who knows what? That's how it jumps species. It can get more lethal. Or not.
In the 1918-19 flu the 3 waves were probably variations in lethality. Mother Nature does provide a check on this. If a virus ever became 100% lethal there'd be nothing left to infect! That's not much help.
There were weaker echoes as late as 1922 but it's reasonable to assume herd immunity may have been kicking in by then. When enough survivors have some immunity the virus has a harder time finding fresh victims.
But the govt didn't do anything back then. They weren't able to develop a vaccine. Social distancing did occur, but only when a population became so terrorized they were afraid to leave the house.
We're doing a lot better this time around, but we better keep our guard up.
