Nov 6 (Reuters) - Most outside advisers to the U.S. Food and Drug Administration voted "no" to whether a successful trial of Biogen Inc's experimental Alzheimer's drug can be viewed as evidence that it is effective without regard for a second, failed study.

They also voted that an earlier-stage study does not offer supportive evidence of Biogen's application for the drug, aducanumab. That vote was 7-0 with 4 "uncertain" votes.

On the first question, two panel members voted "uncertain," with only committee chair Dr. Nathan Fountain, neurology professor at the University of Virginia, voting that the successful trial could stand on its own.

The committee will vote on two more pivotal questions posed by the FDA, including whether Biogen has presented strong evidence that aducanumab has an effect on the progression of Alzheimer's disease.

The data from the successful trial - detailed by Biogen and the FDA at the meeting - "doesn't add up to strong evidence," said committee member Dr. Aaron Kesselheim, associate professor at Harvard Medical School.

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The FDA is expected to make its decision on the drug by March. If approved, aducanumab would be the first new treatment for the disease in decades and the first with evidence that it may be able to slow progression of the fatal, mind-wasting condition, should it win U.S. approval.

The FDA is not obligated to abide by its advisory panel recommendations, but typically does. Biogen shares were halted ahead of the advisory panel meeting.

Alzheimer's disease is the sixth leading cause of death in the United States and there is "a profound and enormous unmet medical need" for new treatments, Billy Dunn, director of neurology products for the FDA's Center for Drug Evaluation and Research, said during the meeting.

The advisory committee on Friday also heard testimony from a number of people suffering from Alzheimer's including several who said they had benefited from aducanumab while enrolled in trials of the drug.

"We know firsthand that it was helping Kevin," said Kim Bonham, speaking of her husband, who was diagnosed with Alzheimer's in 2016.

Biogen in October last year revived its plans to seek approval for aducanumab, months after it had said that an independent futility analysis of its two pivotal trials showed they were unlikely to succeed.

The company said it changed course after a new analysis showed a high dose of the drug could slow disease progression.

The FDA staff earlier this week said data from one of the trials "provides the primary evidence of effectiveness" and a clinically meaningful treatment effect.

They said failure of a second large trial did not detract from the findings of the positive study.

(Reporting by Manojna Maddipatla in Bengaluru; Editing by Bill Berkrot)