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Tiered Use of Inactivated Influenza Vaccine in the Event of a Vaccine Shortage

The United States has experienced disruptions in the manufacture or distribution of inactivated influenza vaccine during three of the last five influenza seasons (1--3). Delays in delivery of influenza vaccine or vaccine shortages remain possible, in part, because of inherent time constraints in manufacturing the vaccine, given the annual updating of influenza vaccine strains and uncertainties regarding vaccine supply (including licensure of new vaccine preparations). Although total vaccine supply for the 2005--06 influenza season is not yet known, the minimum anticipated supply is approximately 58--60 million doses of inactivated vaccine and 3 million doses of live, attenuated vaccine. This estimated supply is similar to that available during the 2004--05 season and would be adequate to satisfy historical demand for influenza vaccine among persons considered by the Advisory Committee on Immunization Practices (ACIP) to be at high risk for serious complications associated with influenza virus infection, health-care workers, and household contacts of children aged <6 months (Table). These groups were prioritized for influenza vaccination in 2004--05 (3). Additional doses of inactivated influenza vaccine might be available for the U.S. market in 2005--06, but this cannot yet be confirmed. Availability of additional vaccine would allow for expansion of the priority groups and, preferably, vaccination of all persons who desire it.

During periods of inactivated influenza vaccine shortfall, vaccination is prioritized on the basis of risk for serious influenza-associated complications. CDC and ACIP recommend use of vaccination priority groups only in the event of vaccine supply disruptions. At present, CDC and ACIP do not recommend prioritization of inactivated influenza vaccine for the 2005--06 season. Current recommendations for use of influenza vaccine were published recently (4). However, to help vaccine providers develop contingency plans for the upcoming influenza season in the event of a shortfall, this report details the priority groups for vaccination (Table). Announcement of a need for prioritization will be made promptly upon receipt of information indicating a potential disruption to the vaccine supply, if necessary.

ACIP and CDC determined the priority groups, ranked in three tiers, on the basis of influenza-associated mortality and hospitalization rates (Table). In the event of an influenza vaccine shortfall, persons in tier 1 should be vaccinated preferentially, followed by persons in tier 2, then persons in tier 3. On rare occasions when local vaccine supply is extremely limited, state and local health officials and vaccination providers should prioritize persons in group 1A before all other groups. However, in all other vaccine shortfall situations, persons in groups 1A, 1B, and 1C should be considered equivalent and should be vaccinated simultaneously. Eligible persons in group 1C and tiers 2 and 3 should be encouraged to receive live, attenuated influenza vaccine during periods of inactivated influenza vaccine shortfall.


  1. CDC. Updated recommendations from the Advisory Committee on Immunization Practices in response to delays in supply of influenza vaccine for the 2000--01 season. MMWR 2000;49:888--92.
  2. CDC. Delayed influenza vaccine availability for 2001--02 season and supplemental recommendations of the Advisory Committee on Immunization Practices. MMWR 2001;50:582--5.
  3. CDC. Interim influenza vaccination recommendations, 2004--05 influenza season. MMWR 2004;53:923--4.
  4. CDC. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2005;54(No. RR-8).


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Date last reviewed: 8/3/2005


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