Merck's Varivax Approval Delayed

Approval in the USA of Merck & Co's varicella-zoster virus (VZV) vaccine, Varivax, awaits data from the company on contamination issues related to the vaccine's production. The Food and Drug Administration'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."

Merck has been trying to get approval for the chickenpox vaccine for almost a decade. Varivax last went before the advisory panel in January 1994, and was recommended for approval. Many of the questions raised at that time, including long-term efficacy and follow-up studies, have now been answered, but the FDA still wants to confirm that retroviral contamination is not an issue. The agency is in the process of receiving data from the company from retroviral testing studies.

Meantime, Merck has tentatively agreed to carry out certain Phase IV studies on the vaccine to look prospectively at long-term antibody levels and the efficacy of the vaccine when used in conjunction with other vaccines. These studies will likely use disease manifestation as endpoints rather than serological markers, and will provide data to help decide whether it will be necessary to give booster shots.