I suspect that, though with Germ Theory and other advances with preventative/detecting/mitigating mechanisms for anything 'plague'-like, this is in uneasy balance with the Small-World Network that the planet has become.
The late-/post-WW1 influenza outbreak had exceptional 'networking' to help it, whilst the medical advances to deal with it (in all the ways described) were only a fraction of what we'd have today. So it spread, helped (in no small way) by mandated mass movements of men. But relatively few people globe-trotted, otherwise.
The rise in jet-setters in the modern age (leisure and business and everything in-between) then ramped up at te same time as we bacame profficient/lucky enough not to have quite so much a global pandemic threatening to break out at any one time. Until it did... And so lockdowns. (Which, at least on the international level, wasn't something that would have been needed in the days before regular air-mile usage by almost anyone who fancied having a stag-do in Prague or trying to climb Machu Picchu or going over to do a deal with the sweatshop owners in some random African/Asian country or going over to visit the in-laws in Australia or...)
And now (having Been There, Done That, Got The "I've Been Vaccinated" Sticker) there's a mix of over-caution and under-caution for what we all should know is out there and (moreover) what we don't yet know anything solid about. Everyone's probably not much more than half a dozen handshakes from much of the rest of the world's population, but as not everyone is licking their hands after doing so (or Eskimo-greeting each other) then it's probably not as bad as it could be, but not as safe as it might be. Say two-dozen (unlucky and unwise) handshakes between Patient Zero for WhateverComesNext-23, whether it be SARS-like, an influenza, an ebola, a far more agile monkeypox, whichsoever is the one fated to arise next.