"There's still virus being virus present in the secretions and enough of it for a period of time after the fever is gone," Paul O'Keefe, Loyola infectious disease specialist, said.
Not everyone can financially afford to take one more day. In fact it's estimated 50-percent of workers don't get paid if they don't show up for work.
"I don't think it's trivial," O'Keefe said. "It might influence people's decision as to whether they come to work or not, I can't be sure but I suspect it does."
Scientists decided to look at what would happen if employees got paid sick days and even an extra day or two above that for flu.
They used computer models and figured just shy of 12-percent of workers got the flu from workplace transmission and of that nearly three-quarters of that was attributed to coworkers showing up sick.
They simulated two new scenarios: one in which workers had access to paid sick days and another where employees got that one or two extra flu days off, keeping them away even longer.
The results? Universal paid sick time could reduce workplace illness by nearly six-percent. An extra flu day reduced it by over 25-percent and two flu days off -- almost 40-percent.