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<p>They may have heard about it from their parents.</p>
<p>Also, how many days off per year is everyone referring to? Lots of people (including younger ones, perhaps especially younger ones whose immune systems have not “seen” as much) seem to be out for a fair number of days with infectious diseases. It certainly does appear that, in some cases, the number of unscheduled sick days involved here is far greater than the number of scheduled doctor appointments that someone in his/her 50s might have.</p>