Well, an ignorant engineer (me) might point out that one does not receive a flu injection every day of the year. The yearly dose of 25 micrograms works out to 0.07 micrograms per day, averaged over a year.
It is interesting to note that the "mercury in tuna fish" scare sort of evaporated when some bright boy decided to test the mercury levels in a tuna fish caught in the 1800s and lovingly stored in the Smithsonian. Yep; same amount as now, and all those poor folks were busy ingesting tuna fish before they had the EPA or FDA to tell them it was harmful.
--Boris