I don't know for how many years it has been that China was the country developing the Flu Vaccine, however, every year since I was paying attention, China would figure out the 'worst' flu that had appeared that year and then, develop a 'shot' for it.
Then they'd sell it to all the fearful countries who were anxiously waiting to get it.
Another thing was that they'd announce they were running low on their flu shot supply- a perfect way to insure demand.
Also remember -they'd announce there was a wait before it was available - so, we had to wait while China finished their 'magic' of creating the shots.
Not sure when it happened, but most drugs started being made in other countries, rather than the US.
I think Trump talked about bringing drug companies back to the US.