The number of doses of inactivated flu vaccine recommended depends primarily on the age and vaccination history of the recipient:

• For children aged 6 months through 8 years:
  • If they have never been vaccinated for flu before or their vaccination history is unknown, 2 doses are recommended, given at least 4 weeks apart.
  • If they have previously received at least 2 doses of flu vaccine (not necessarily in the same or consecutive seasons), 1 dose is sufficient.
• For individuals 9 years and older, typically only 1 dose per flu season is needed.

The dose volume depends on age and vaccine brand but is generally 0.5 mL intramuscularly for those 3 years and older, and either 0.25 mL or 0.5 mL for children aged 6 to 35 months depending on the product used.