The 2017–18 flu season was the worst in many years. The Center for Disease Control (CDC) estimated roughly 80,000 Americans died as a result of the flu last season, well above any other season’s total in the last 40 years. In addition, the vaccination rate among adults was down to only 37.1%, the lowest in at least seven years, and well below the CDC’s goal of 70%. We set up a randomized controlled trial using our on-demand Creative Focus tool to determine what types of messages may be most effective in persuading people to get a flu shot.