> Genetic analysis and several unusual characteristics of the 1977 Russian flu have prompted many researchers to speculate that the virus was released to the public through a laboratory accident or resulted from a live-vaccine trial escape.
Speculate. Covid shows how easy it is to do just that even if you have current knowledge.
It's not impossible that origin is other than zoonotic however it's very unlikely because that exactly how (nearly?) all viruses came to us.
I already read articles like that over last two years. They started popping up pretty much immediately. And their content didn't change over time. Still just hearsay and tugging on heart's strings.
The problem I have with lab leak idea is not so much that it's not proven, but that it's not falsifiable. You can't prove it's wrong because someone can always tell "maybe they covered it better than we thought!".
https://en.wikipedia.org/wiki/1977_Russian_flu