Federal health advisers endorsed a proposed vaccine yesterday to help prevent shingles, an often-excruciating disease that afflicts as many as 1 million adults every year.

The Food and Drug Administration's advisory panel on vaccines said the vaccine for shingles appeared to be safe and effective in people ages 60 and older. However, panelists worried its effectiveness may not last, and said it appeared to be less effective in people older than 80.

The vaccine, Zostavax, was developed by Merck & Co., which sought to have it approved for use in people 50 and older.

But Merck conducted trials mostly on people 60 and older, leaving the members of the FDA panel on vaccines uncertain whether it was safe or effective for those in their 50s.