Merck’s vaccine to treat shingles has neared the US market, after a nod from an FDA advisory committee.

A US Food and Drug Administration advisory committee has given Merck & Co’s Zostavax an amber light to treat herpes zoster – or shingles – in adults aged over 60.

However, the news does potentially mean a restricted market for Zostavax as the company had hoped to get a nod for all adults over the age of 50. In a statement, the committee members said: “It’s important to acknowledge that [Merck has] shown what is quite an impressive reduction in the instance of herpes zoster in those 60 and over,” but added that the data presented were not sufficient to support Merck’s proposed use for the vaccine in adults ages 50-59.

“Obviously, we cannot say there are any data to support licensing between ages 50 to 59. It’s unfortunate in the sense that my guess is it will work once the company actually does the studies,” committee member David Markowitz (University of Michigan) remarked. “Until we have the studies we can’t really comment.”

Only about 150 of the 38,000 patients in Merck’s Zostavax study were in the 50-59 year age range. The FDA panel members seemed concerned that immunizing people in their 50’s would mean the vaccine reduces in efficacy over time, and would open the door to herpes zoster and post-herpetic neuralgia at a point in life when the risk of severe pain is greater.

Merck disagrees with this point, but has said that it does plan to investigate the efficacy of a booster dose in future studies. In data submitted to the FDA, Zostavax reduced the incidence of shingles by 51% compared to placebo and reduced the symptom burden among patients in whom the disease did occur.

Shingles is caused by a reactivation of the chickenpox virus and can lead to long-term complications, including severe nerve pain, or post-herpetic neuralgia.

Meanwhile, after a bad year following the withdrawal of its arthritis drug Vioxx (rofecoxib), the US giant will likely be hoping observers will turn a favourable eye on its product pipeline after the same advisory committee recommended its rotavirus Rotateq vaccine for approval last week and the company on December 1 sought marketing clearance for its Gardasil cervical cancer vaccine.