Production hitch stems US supply of ProQuad combination vaccine

With Merck, the only US supplier of vaccines containing varicella zoster virus, prioritising production of its varicella (Varivax) and zoster (Zostavax, for shingles) vaccines, the company has informed the US Centers for Disease Control and Prevention (CDC) that ProQuad will be available only on a limited basis until July. Current order projections "indicate ProQuad will be unavailable beginning in July 2007, although timing will depend on market demand",​ the CDC said. Once the existing supply is depleted, ProQuad is not expected to be available for the rest of the year. Merck has asked customers to start switching over from ProQuad to Varivax and the company's combined measles, mumps and rubella vaccine (M-M-R II) "at their earliest convenience"​, the CDC stated. ProQuad was approved by the US Food and Drug Administration in September 2005. Merck could not be reached for comment on what caused the VZV shortage or whether the problem has been remedied. The company notified the CDC back in February that it had obtained lower than expected amounts of the virus in recent manufactured bulk vaccine. Varicella bulk is stored frozen until it is needed in the final preparation phase of each vaccine, the CDC noted, adding that Merck had suspended production temporarily while it identified the cause of the low virus yield. The decision to prioritise continued production of Varivax and Zostavax was taken because manufacturing varicella vaccine required less VZV than manufacturing ProQuad, the CDC explained. And although zoster vaccine production called for a similar amount of VZV as for ProQuad, projected supply needs for Zostavax were much lower than for ProQuad. Merck would also be stepping up production of M-M-R II, the CDC added. As the agency noted in its latest update on the VZV shortage, Merck expects to continue to meet demand for Varivax and M-M-R II to implement fully the recommended US immunization schedule. This includes routine doses of each vaccine for children at 12-15 months and 4-6 years, catch-up vaccination with a second dose for children or adolescents who received only one dose, and vaccination with two doses for other children, adolescents and adults without evidence of immunity. The current supply of Zostavax is expected to be adequate for routine vaccination of adults aged 60 years and over, the CDC said.