Frequently Asked Questions on Vaccine Supply

Questions & Answers

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Get the latest on influenza vaccine supply for 2021-2022 season.


With more manufacturers producing influenza vaccine for the United States, can we still anticipate experiencing disruptions to the influenza vaccine supply?

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, and in fact, such problems have impacted the supply in prior influenza seasons.

Has CDC created an influenza vaccine stockpile to address vaccine supply disruptions?

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. Since in most years, influenza disease activity does not peak until January or later, this approach of stockpiling can be quite useful if vaccine production delays or shortages drive demand later into the influenza vaccination season.

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Why is vaccine supply left over at the end of each influenza season?

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 with vaccine coming off the production line in middle or late November or later may not be able to sell it all and providers receiving vaccine in this same time frame may not be able to convince patients to receive it, even though late season vaccination is encouraged and mostly beneficial.

What is the status of thimerosal in influenza vaccines?

At the present time, all six manufacturers licensed in the United States produce at least one formulation that is thimerosal-free or preservative-free (trace thimerosal). See the Table: Influenza Vaccine Manufacturers for the 2021-22 Influenza Season.

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Why can’t CDC control the distribution of influenza vaccine so that providers seeing priority patients receive their orders first?

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

CDC encourages influenza vaccine manufacturers and distributors to use a distribution strategy that provides vaccine to all provider types in a comparable timeframe. Such an approach allows the broadest possible access for vaccine throughout the season and is consistent with national data that indicate adults in the U.S. receive influenza vaccine in a wide variety of venues, including private provider offices, worksites, clinics, hospitals, health departments, retail settings, and senior centers. While there is a relationship between age or health status and the location in which vaccines are received, the data demonstrate that all of these venues serve at least some older adults or higher risk patients.

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It seems that my vaccines come in multiple shipments during the season, which makes planning difficult. Why can’t vaccine be ready and delivered prior to the beginning of the vaccination season?

The timing of the completion of influenza vaccine production varies from year to year and depends upon on a number of factors, including the strains chosen for inclusion in the vaccine. Even in a year in which each step of production goes well, since influenza vaccine manufacturers are currently producing vaccine at or near full capacity, it isn’t possible for all of the doses to be produced and distributed before the beginning of the vaccination season.

To allow as many providers as possible to begin vaccinating early in the season, CDC encourages manufacturers and distributors to use a distribution strategy in which partial shipments are used to allow as many providers as possible to begin vaccination activities early in the vaccination season. Ideally, the intervals between shipments are short so that each provider has a continuous supply and can continue vaccinating patients without interruption.

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Why can’t influenza vaccine manufacturers and distributors always provide reliable information about when vaccine shipments are scheduled?

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.

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Why is there so much variation in when different vaccination providers receive their vaccine?

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.

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Why do manufacturers and distributors take a phased approach to vaccine distribution?

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 making 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.

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What role does the Department of Health and Human Services play in the supply and distribution of the seasonal influenza vaccine?

Influenza vaccine production and distribution are primarily private sector endeavors. The Department of Health and Human Services and CDC do not have the authority to control influenza vaccine distribution nor the resources 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.

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