Influenza viruses change from year to year, so influenza vaccines must be updated annually to include the viruses that will most likely circulate in the upcoming season. Once the viruses are selected for the new formulation, private manufacturers produce, test, release and distribute influenza vaccine.

Flu vaccine is produced by private manufacturers, so supply depends on manufacturers. Vaccine manufacturers have projected that they will supply the United States with as many as 173.5 million to 183.5 million doses of influenza vaccines for the 2022-2023 season. These projections may change as the season progresses. All flu vaccines for the 2022-2023 season will be quadrivalent (four component). Most will be thimerosal-free or thimerosal-reduced vaccine (93%), and about 20% of flu vaccines will be egg-free.