More Review for Merck Vaccine

Shares of Merck (MRK Quote) slipped Friday after the Food and Drug Administration said it needed more time to review the company's shingles vaccine Zostavax.

Merck was supposed to hear the FDA's verdict by the end of February, but the company said the agency wants 90 more days to review the drug. Merck didn't explain why the FDA asked for more time. Merck's stock was off 20 cents to $35.21.

Merck submitted an application in April, seeking approval for vaccinating people over age 50. Zostavax would be the first vaccine for shingles, also known as herpes zoster. The condition is caused by a reactivation of a latent virus that causes chickenpox. Shingles is a viral infection of nerve roots that can cause burning and tingling sensations, a rash or skin blisters.

In December, an FDA advisory committee recommended the drug for people 60 years and older. The panel of medical experts said Merck didn't provide the necessary clinical data for people ages 50 through 59.

Zostavax is one of three Merck vaccines being considered this year. Three weeks ago, the agency approved Rotateq for protecting infants and young children against a virus that causes debilitating diarrhea.

Earlier this month, the FDA granted an expedited review of Gardasil, a vaccine against human papillomavirus, which causes cervical cancer. The agency is scheduled to act in early June.