Merck's Varicella Production Issues Remain, Validation Expected Soon

Merck expects to complete validation of bulk varicella production in the coming months as it continues to correct manufacturing issues that have created supply disruptions for its varicella-containing vaccines ProQuad and Zostavax.

“We need a few more months to be able to show sustainability in that the processes have been validated and that the filings to the FDA are the right ones,” Merck CEO Dick Clark told analysts during the firm’s 2008 earnings guidance conference call.

The varicella-manufacturing issues, which made the ingredient subpotent and not fit for use in ProQuad, forced the firm to halt distribution of its combination measles, mumps, rubella (MMR) and chickenpox vaccine.

When the company announced the resumption of bulk varicella production last summer, it said the issues leading to the shortage of ProQuad would not affect the availability of other varicella-containing vaccines, Zostavax (zoster vaccine live) for the prevention of shingles and Varivax (varicella virus vaccine live) for the prevention of chickenpox. However, the availability of the refrigerated formulation of Zostavax has been affected.