Merck's Varivax Finally Approved In USA

Merck & Co's chickenpox vaccine Varivax has been approved by the Food and Drug Administration and should be launched in the USA within the next two months. Merck submitted the latest dossier for the product in January 1993, but the company has been trying to get a chickenpox vaccine onto the market for several years.

At the last hurdle, Merck had to provide data on contamination issues related to the vaccine's production. The FDA's medical officer for antiviral drugs, Philip Krause, told the Vaccines & Related Biological Products Advisory Committee at its meeting on January 27 that the agency was waiting for data which would show that the cells in which the product is made are free of "adventitious agents" such as retroviruses.

The major factor which has held back the vaccine on its way to market has been production problems, and at a press conference to publicize the approval on March 17, the company discussed the changes in the manufacturing process which it had to implement. Most of these revolved around difficulties in keeping the product frozen - the vaccine must be kept at -15oC to -20oC, according to the approval letter from the FDA.