My understanding is that it is very labor intensive and the manufacturing capacity is simply not there to make billions of doses in a short timescale (months).

My understanding is that it is very labor intensive and the manufacturing capacity is simply not there to make billions of doses in a short timescale (months). https://en.wikipedia.org/wiki/Influenza_vaccine#Manufacturing https://en.wikipedia.org/wiki/Influenza_vaccine#Manufacturin...