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Notice to Readers: Supply of Vaccines Containing Varicella-Zoster Virus

CDC received notice from Merck & Co., Inc., that it has lower amounts of varicella-zoster virus (VZV) than expected from recently manufactured bulk vaccine. Bulk vaccine production is an intermediate step in the manufacture of VZV-containing vaccines. Varicella bulk is stored frozen until it is needed in the final preparation phase of each vaccine. Production of VZV bulk has been suspended temporarily while the manufacturer identifies the cause of the low virus yield. Merck is the only U.S. supplier of VZV-containing vaccine, including varicella vaccine (Varivax®); combined measles, mumps, rubella, and varicella (MMR-V) vaccine (ProQuad®); and zoster vaccine (Zostavax®). This lower virus yield does not affect the quality of any of Merck's VZV-containing vaccines currently on the market, any lots of vaccine manufactured and ready for release to the market, or any VZV-containing vaccines presently being manufactured.

To conserve existing bulk vaccine with adequate VZV potency, Merck is prioritizing continued production of varicella and zoster vaccines over production of MMR-V vaccine. Merck is taking this approach because the production of varicella vaccine requires less VZV than the production of MMR-V vaccine. Although zoster vaccine requires a similar amount of VZV for production as MMR-V vaccine, projected supply needs for zoster vaccine are much lower than projected supply needs for MMR-V vaccine. Merck also will increase production of combined measles, mumps, and rubella (MMR) vaccine (M-M-R II®).

Current supply assessments in the United States indicate that this interruption in bulk vaccine supply will not affect the supply of either varicella vaccine or zoster vaccine. The U.S. varicella vaccine supply is expected to be adequate to fully implement the recommended immunization schedule for varicella vaccine for all age groups, including the routine 2-dose schedule for children at 12--15 months and at 4--6 years, catch-up vaccination with the second dose for children and adolescents who received only 1 dose, and vaccination with 2 doses for other children, adolescents, and adults without evidence of immunity (1--3). For zoster vaccine, the supply is expected to be adequate to vaccinate adults aged >60 years in accordance with current provisional vaccine policy recommendations (4). The MMR-V vaccine supply is adequate to continue ordering this combination vaccine (5); however, the manufacturer expects supplies of MMR-V vaccine to be depleted toward the end of 2007, depending on market demand. When this occurs, supplies of separate MMR and varicella vaccines are expected to be adequate to fulfill the need for these two products in place of MMR-V vaccine. CDC will continue to work with Merck and vaccine-provider stakeholders to monitor the supply of VZV-containing vaccines. Updates on vaccine shortages and delays are available at


  1. CDC. Prevention of varicella: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1996;45:(No. RR-11)1--35.
  2. CDC. Prevention of varicella: updated recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1999; 48(No. RR-6):1--5.
  3. ACIP provisional recommendations for prevention of varicella. Available at
  4. ACIP provisional recommendations for use of zoster vaccine. October 2006. Available at
  5. CDC. Notice to readers: licensure of a combined live attenuated measles, mumps, rubella, and varicella vaccine. MMWR 2006; 54:1212.

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Date last reviewed: 2/22/2007


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