Given the choice of getting a flu vaccine or wearing a mask during flu season, 90 percent of workers at a California hospital chose a vaccine, researchers say. Study co-author Dr. Susan Huang of the University of California Irvine Medical Center said the hospital began a systematic effort to raise vaccination rates among its 6,500 employees in 2006. Initial efforts focused on educating employees, making vaccines available conveniently and free of charge. During the 2007-2008 flu seasons, efforts were advanced to include the use of mobile carts and decentralized vaccine distribution by designated nurses in clinical areas.This voluntary campaign raised rates from around 45 percent to 60 percent, Huang said. \"Only the addition of a mandatory vaccination policy enabled instantaneous gains in vaccination to levels more than 90 percent,\" the researchers said in a statement. The mandatory campaign -- requiring vaccination or wearing a mask while in medical areas during flu season from December to March -- raised vaccination rates in the 2009 flu season to nearly 87 percent. In addition to the mask requirement, employees who were not vaccinated were required to sign a written declination and a real-time tracking tool was implemented to provide online-accessible lists of compliant and non-compliant staff, Huang said. This modification, as well as the cumulative strategies initiated after 2006, raised flu vaccination rates among school of medicine faculty to more than 90 percent.The findings were published in the journal of the Society for Healthcare Epidemiology of America.