I provided one link to the SE Asia origination of flu in my post above. There's plenty more information out there.
Obviously it can technically originate/mutate from anywhere, but most come from South, East, and SE Asia due to climate and population density.
If the flu in every place was simply due to local mutation, then developing a vaccine each year would be impossible.
Instead - there are mutations from source locations, that then spread seasonally. That's how they can pick which strains to put in the vaccine before it arrives in Northern temperate climates.
Obviously it can technically originate/mutate from anywhere, but most come from South, East, and SE Asia due to climate and population density.
If the flu in every place was simply due to local mutation, then developing a vaccine each year would be impossible.
Instead - there are mutations from source locations, that then spread seasonally. That's how they can pick which strains to put in the vaccine before it arrives in Northern temperate climates.
