Turns out continued message repetition in public health or safety campaigns may have contradictory effects among older adults:
"Repeatedly identifying a claim as false helped older adults remember it as false in the short term but paradoxically made them more likely to remember it as true after a 3 day delay. This unintended effect of repetition comes from increased familiarity with the claim itself but decreased recollection of the claim's original context."
From the March issue of the Journal of Consumer Research. Thanks to Paul Kedrosky for the pointer.