Seasonal Influenza Vaccine Supply Frequently Asked Questions

Manufacturers project 148 million flu vaccines for 2024-2025; most will be thimerosal-free and egg-based.

CDC is not aware of any supply problems with these higher-dose or adjuvanted influenza vaccines as a group; however, influenza vaccine manufacturers are the best source for information on supplies of their influenza vaccines.

For the 2024-2025 season, manufacturers will produce influenza vaccine doses that do not contain thimerosal and some vaccines that do. Only multidose vial formulations of influenza vaccines will contain thimerosal.

Most of projected influenza vaccine supply produced this influenza season will be thimerosal-free or thimerosal-reduced (i.e., preservative-free).

For the 2024-2025 season, 100% of the projected vaccine supply produced will be trivalent (three-component) vaccines.

Most of the projected vaccine supply produced for the 2024-2025 flu season will be produced using egg-based manufacturing technology. The remaining vaccine will be produced using cell-based or recombinant technology.

Flu vaccine demand usually peaks in October or November but may not match production timing, affecting availability and uptake. Flu vaccine production timing is unpredictable, so supply may not match peak demand.

Influenza vaccine pre-booking typically occurs between January and March. Some formulations of vaccine may still be available for purchase. Providers should contact distributors and local vendors about remaining supply. In addition, beginning in early October each year, information about manufacturers and distributors who still have influenza vaccine available for sale.

Updates on the distribution of influenza vaccine doses for the 2024-2025 season will be provided as the season progresses.

Influenza vaccine pre-booking typically occurs between January and March. Some formulations of vaccine may still be available for purchase. Providers should contact distributors and local vendors about remaining supply.

Influenza vaccine distribution has begun for the 2024-2025 influenza season. People should consult CDC's guidance on the best timing for getting their vaccine.

Currently, influenza vaccine manufacturers are not reporting any expected delays in national influenza vaccine supply or distribution this season. Call ahead to check availability.

Influenza vaccine production and distribution in the United States are primarily controlled by the private sector. CDC does not have the authority, or relationships with providers necessary to carry out or control vaccine product or distribution.

CDC advises equitable vaccine distribution across all provider types to ensure broad access and reach diverse vaccination venues. CDC also advises smaller, frequent vaccine shipments to ensure broad provider access early in the season.

The timing of influenza vaccine production varies from year to year and depends on multiple factors, including the viruses chosen for inclusion in the vaccine. Even in a year in which each step of production goes well, it isn’t possible for all of the doses to be produced and distributed before the beginning of the vaccination season because influenza vaccine manufacturers already produce vaccine at or near full capacity.

Because of the unpredictable nature and complexity of biologics production, it is not always possible to anticipate when vaccine lots will be completed and released. Distributors must rely on the manufacturers to provide them with this information. Both manufacturers and distributors are reluctant to project very far into the future about when shipments will be made because they do not want to create unrealistic expectations among customers.

The primary reason for the variation in timing is because different types of vaccine providers receive their vaccine from different sources. A provider may order influenza vaccine (1) directly from the manufacturer; (2) from a distributor, who is a customer of the manufacturer; or (3) from a secondary distributor, through whom the provider also receives other medical products. Some of these routes of distribution are more direct than others, which can affect the timing of vaccine delivery.

Flu vaccine production starts 6-9 months before distribution, which occurs in phases, ending by early December. This may result in some uncertainty that makes it difficult for vaccine providers to plan their vaccination activities. Manufacturers and distributors try to get some vaccine to as many providers as possible as early as possible so that they can begin vaccinating their patients.

Seasonal influenza vaccine production and distribution are primarily controlled by the private sector. The Department of Health and Human Services and CDC do not have the authority to control influenza vaccine distribution. However, the Department has made significant efforts to enhance production capacity of seasonal influenza vaccines, including supporting manufacturers as they invest in processes to stabilize and increase their production capacity.

The challenges associated with the U.S. influenza vaccine supply are multi-faceted. 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, manufacturers operate under a very tight timeline for producing, testing, releasing, and distributing the vaccine. Due to these time constraints, any problems encountered during production may cause shortages or delays. Such problems have impacted the influenza vaccine supply in some prior influenza seasons.

Beginning in 2004, CDC began purchasing a late-season influenza vaccine stockpile to provide a limited quantity of vaccine for children (using Vaccines for Children [VFC] Program funds) to address urgent supply problems that may exist in December, January or beyond. In most years, influenza disease activity does not peak until January or later, so this approach of stockpiling can be quite useful if vaccine production delays or shortages drive demand later into the influenza vaccination season.