@Catmo- you'd be lucky to have a global population of 200 million in 1965 under that scenario. Remember, it zaps the adults and therefore, the folks likely/able to breed, making for a heck of a demographic bottleneck.
For example, it would look a lot like what we see in AIDS-devastated Africa where you've got lots of little kids and old farts, but working/breeding age population's down 80-90%.
That's with AIDS infecting 50% of the kids at birth.
This scenario's
worse b/c After a quick wiki consult, what was really bad about Spanish flu was how it killed pregnant women 70% of the time OTL, and those that survived miscarried 75% of the time. So very few kids, lots of old farts, and thus maybe 5% of the breeding population you had before.
A 40% dieback a la European Black Plagues 1300-1500 meant the surplus population that allowed for social stasis in the High Middle Ages no longer exists, the evolution from land-to-cash-based economy, etc. that had social benefits in the long run. Plus, the Church had significantly less influence on the plague survivors allowing the Renaissance to go on.
An 80-90% dieback of breeding/working age population is a recipe for Mad Max-level societal meltdown especially in a pre-Information Age society. Modern society is like a pyramid balanced on a very small point.
Without .05% of the population amply feeding the rest of the population and allowing everyone else to be technically and commercially clever, social progress screeches to a halt and often bounces back to medieval village society at best.
Earth Abides by George Stewart is one literary treatment of what happens when population gets reduced so far that it doesn't have the critical mass of population allowing for preservation of modern skills.
FWIW, several nations managed to initiate quarantines of foreign ships and substantitally reduce deaths like Japan. Several major issues prevented a more effective quarantine response throughout the world in 1918-1920.
- lack of WHO to coordinate public health information, quarantine sick and immunize vulnerable populations. Radio existed then as did the telegraph, but wartime censorship crippled efforts to coordinate an effective international response.
- As mentioned in Wiki, people were dealing with endemic outbreaks of cholera, polio, typhoid, and malaria that killed folks by the millions in rich and poor countries alike. A war was going on and folks were dying in droves anyway.
- As said before, WWI and its political sequelae profoundly buggered food production and distribution as well as bankrupting governments everywhere, leaving a huge vulnerable population in Europe and elsewhere without food, money or functional political systems to take the necessary public health/sanitation steps to stop/prevent its spread.
I thought I'd throw a little food for thought into the mix.
