Researchers boosted flu shots by asking employees to write down a time

Seasonal flu causes over 200,000 US hospitalizations a year, and the vaccine that prevents most of them is cheap and, at many large employers, free and delivered on-site during work hours — every practical objection an employer can remove (cost, travel, scheduling) had already been removed.

Five researchers ran a three-arm randomized trial at a large Midwestern utility company to test a different theory: psychology research on 'implementation intentions' had shown, mostly in small lab studies, that asking someone to specify WHEN and WHERE they'll act closes a gap that reminders and information don't touch — the gap between deciding to do something and actually doing it.

Asked employees to write down a date and time, forging a mental trigger that turns a vague intention into a cued action, with no follow-up.

Writing a specific time converts a vague intention into a cued action.

The written moment becomes a trigger that fires when it arrives.

A date alone leaves the moment unscheduled, so only the time prompt worked.

The effect was stronger where fewer clinic days left less room for vague plans.

When people already intend to act, prompt them to specify when and where; a concrete plan bridges the gap between intention and action.

The control group's vaccination rate was 33.1%. The date-only prompt raised it to 35.6%, a 2.4-point gain that was not statistically significant. The date-and-time prompt raised it to 37.1%, a 4.0-point gain (regression-adjusted 4.2 points, p=.03) that was both significant and, for a single line of ink costing nothing to print, of meaningful magnitude — comparable to gains employers spend real money chasing through incentives or extended clinic hours.