Infectious diseases are out of whack

A little while ago I finished reading Plagues Upon the Earth: Disease and the Course of Human History.  It was a a very good book about exactly what it says on the tin.  There was a bunch of fascinating science in it but one part clarified some ideas I'd had noodling around in my head prompted by Covid and I'm going to outline those bits here.

Back in prehistory there were very few epidemic diseases spread from human to human.  In a band of 100 people a disease like influenza will rip through everyone in short order.  But afterwards, everybody's immunity will be at a peak and that disease lineage would die out.  This isn't to say that humans would never get the flu, just that each outbreak would be the result of a new zoonosis or crossover from animals to humans.  Other diseases like Cholera exist harmlessly in the environment most of the time, attaching to the shells of crabs, until some human happens to drink it in and then it expands out of control with us as just civilian casualties in an ongoing war.

Modern infectious diseases like flu requires large connected populations that they can spread in so as not to exhaust their supply of hosts.  And in terms of connection and size the modern world is a treasure trove indeed.  Most of the infectious diseases we're familiar with aren't long companions of humanity, they're recent guests that have arrived in the last few hundred years.

Going beyond the book now, it seems clear that if we had developed to 1850s levels of technology and population then that wouldn't have been sustainable.  More and more zoonotic crossovers would have happened causing new circulating epidemics until eventually populations would have been reduced to sustainable levels.  But medical technology advances with inoculation, modern sanitation, vaccination, antibiotics, etc.  They have, in fact, more than made up for the introduction of new diseases over the last hundred years and we are far better off in terms of disease burden than we were a hundred years ago.  

But still, we're in a Red Queen's race where we have to run very hard just to keep our place.  Recently we had a new medium seriousness (now that we're all vaccinated) respiratory disease introduced to the world alongside flu and it won't be going away with modern technology.  Maybe a new generation of nasal vaccines will come along to better control the infectiousness of respiratory diseases than current vaccines and we'll be able to eliminate Covid and the Flu.   But even then we're still in the same position we've been in for much of history: out of equilibrium and praying for medical advances before the equilibrium catches up with us.