I think the leading theory, here's another: https://www.nationalgeographic.com/news/2014/1/140123-spanish-flu-1918-china-origins-pandemic-science-health/ https:

I think the leading theory, here's another: https://www.nationalgeographic.com/news/2014/1/140123-spanish-flu-1918-china-origins-pandemic-science-health/ https://www.nationalgeographic.com/news/2014/1/140123-spanis...