Employers who offer the flu vaccine to workers in hopes of reducing lost work days may not be reaping any economic benefits in return. Although an earlier report indicated that the vaccine saved businesses $46.85 per shot, research published yesterday in the Journal of the American Medical Association suggests that in most years, vaccinating healthy adults may not be cost-effective.

In fairness, though, when it comes to flu vaccines, evaluating cost-benefit is a tricky business. Certainly the shots serve the elderly, who are more susceptible to flu-related complications, yet these people are less likely to be in the workforce. Other factors include the severity of the flu season, which varies from year to year, and the fact that sometimes the vaccine doesn't even match that season's circulating flu strain. All told, said University of Michigan epidemiologist Arnold S. Monto in an accompanying editorial, the new study indicates that "given the unpredictability of the size of a forthcoming outbreak, vaccine has to be given every year, and unless there is much illness to prevent, the costs outweigh the benefits."