In fact, based on the initial footage from Wuhan, countries should have adopted more stringent protocols when they repatriated their nationals, i.e. quarantine on arrival etc... If in doubt throw everything including the kitchen sink at just to be sure. But it is what it is. I just hope we've learnt from this and are prepared for the next one.
The 1977 H1N1 spread was never truly explained, here a possible lab incident in Russia was one of the possibilities:
https://journals.asm.org/doi/10.1128/mbio.01013-15?permanent...
The Coronavirus from Wuhan, China has a similar story, only this time it is in China.
https://www.reuters.com/business/healthcare-pharmaceuticals/...
To me a solid scientific explanation is still useful, e.g. the intimate study of the Wuhan lab into Coronavirus seems risky at best.