Authorities are urging just about everyone to get one, except babies less than 6 months old and people with severe allergies to the eggs uses to brew the vaccine.
There's a special high-dose version for people 65 or older. The Centers for Disease Control and Prevention says it plans to track whether the higher dose leads to less illness, but it's fine to choose either version.
Most people will need just one shot.
A record supply of the flu vaccine is expected to be available.