I'd add that the article does not state that there have never been cases of accidental releases of pathogens from laboratories, only that such accidents had lik

I'd add that the article does not state that there have never been cases of accidental releases of pathogens from laboratories, only that such accidents had likely not led to a 'global epidemic' as of the date the article was written (2015). The article's abstract opens with the statement 'The 1977-1978 influenza epidemic was probably not a natural event'.