Bird flu vaccine’s protection slips

The nation’s first vaccine against bird flu is even less effective than previously thought, according to Food and Drug Administration documents released Monday.

In clinical trials, the two-shot series appears to provide protection to just 45% of adults who received the highest dose of Sanofi Aventis’ vaccine.

An interim analysis of the study suggested the vaccine sparked a protective immune response in 54% of patients when measured 28 days after the second shot. The New England Journal of Medicine published those results in March 2006.

The FDA released the more recent results, contained in company and agency documents, ahead of a meeting today at which it will ask outside experts to review the vaccine.