Seasonal Influenza Vaccine Supply for the U.S. 2023-2024 Influenza Season (2024)

Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2023-2024 Influenza Season has been published.

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 2023-2024 season, 100% of the projected vaccine supply produced will be quadrivalent (four component) vaccines. There will not be any trivalent influenza vaccine available.

Approximately 79% of the projected vaccine supply produced for the 2023-2024 flu season will be produced using egg-based manufacturing technology. The remaining vaccine will be produced using cell-based or recombinant technology.

Information about vaccine supply is available here.

Demand for influenza vaccine varies from year to year. Within each influenza vaccination season, demand varies by month, usually peaking in October or November and rapidly declining after that. Meanwhile, because timing of influenza vaccine production and distribution is unpredictable, availability of the vaccine supply does not always coincide with peak demand. Thus, manufacturers that produce vaccine in middle or late November or later may not be able to sell it all, and patients may be less willing to receive vaccine in this same time frame from providers who have vaccine available, even though late season vaccination is encouraged and mostly beneficial.

Influenza vaccine distribution has begun for the 2023-2024 influenza season. People should consult CDC’s guidanceon the best timing for getting their vaccine.

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.

Manufacturers say that because of the unpredictable nature and complexity of biologics production, they cannot always 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, from 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.

Influenza vaccine production begins as early as 6 to 9 months before the beginning of vaccine distribution. Even with this early start, it isn’t possible to complete the entire production and distribution process prior to flu season, in part because of the limited number of influenza vaccine manufacturing plants in the United States and the large number of doses that are produced each year. Instead, influenza vaccine distribution takes place in a phased fashion over a number of months. Distribution usually begins in late summer and is complete near the end of November or early in 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.

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, to manage such an effort. 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.