During flu season, in working adults ages 50 to 64 years old, flu-like illness is responsible for 45% of workdays lost and 49% of low-productivity days.
Nichol, Kristin L., April Lind, Karen L. Margolis, Maureen Murdoch, Rodney McFadden, et al. The Effectiveness of Vaccination Against Influenza in Healthy, Working Adults. NEJM. 1995; 333(14): 889-93. http://www.nejm.org/doi/full/10.1056/NEJM199510053331401