Dec 23 (Reuters) - Biogen Inc (BIIB.O) and Japanese partner Eisai Co (4523.T) said on Thursday the U.S. Food and Drug Administration (FDA) had granted "fast track" designation to their experimental therapy, lecanemab, for the treatment of early Alzheimer"s disease. FDA had granted "breakthrough" therapy designation to the drug earlier this year despite an outside advisory panel saying its clinical benefit was unproven. read more The drug works in a similar manner to Biogen"s Aduhelm and gets rid of sticky deposits of a protein called amyloid beta from brains of patients in the initial stages of the disease to mitigate its impact. The fast track status is designed to expedite the review of treatments and vaccines meant for serious conditions. A vaccine or treatment that gets the status is eligible for more frequent meetings with the FDA. The companies have jointly developed three experimental drugs for the disease, which affects millions around the world and has not seen a new treatment in decades. The drug"s development was nearly abandoned after disappointing trial results in 2019, but Biogen revived it after reviewing data that showed higher doses of the drug could slow disease progression.