In separate votes, the outside panel said the vaccine was both safe and effective. A vaccine must meet both standards to win approval from the Food and Drug Administration. The votes came after FDA officials said the Sanofi Aventis SA vaccine still could play an important role in protecting against the increased likelihood of a pandemic, despite its limited effectiveness.

The FDA is not required to follow the advice of its advisory committees, but usually does. The vaccine produced by the Paris-based company is the first against the H5N1 influenza strain to seek U.S. government approval.

The vaccine already is being stockpiled, even without FDA approval, for eventual interim use to protect emergency workers and others in a pandemic. It would be used until better vaccines could be developed. Though not required, FDA approval would state the agency's opinion on the vaccine's safety and effectiveness, said Dr. Jesse Goodman, FDA's chief of biologic products.

In a clinical trial, the two-shot series appears to provide protection to just 45 percent of adults who received the highest dose. An earlier, interim analysis of the same study had suggested it prompted a protective immune response in 54 percent of patients, when measured 28 days after getting the second of two shots. The FDA said it would like to see a response in at least 70 percent of those vaccinated against bird flu.

"The more antibodies, the better. But even at lower levels, there is a possibility of protection," Goodman told reporters on the sidelines of the meeting.

The government plans to buy and stockpile enough bird flu vaccine for 20 million people, including emergency and health care workers. The Sanofi vaccine wouldn't be sold commercially.