Event study with standard errors clustered at county and date levels.
(Third, it is possible that those affected by the ad chose to schedule vaccine appointments for several days or a week in the future rather than getting vaccinated on the day they viewed the ad. Even for vaccines administered as walk-ins, rather than scheduled appointments, it is plausible that the advertising campaign had an effect with a lag, with viewers’ changing attitudes being reflected in actual vaccinations only after several days or a week of the attitude change. For example, viewers may decide, consciously or not, “I won’t go out of my way to get the vaccine today, but I’ve decided to go ahead with getting vaccinated next time I find myself in a drugstore.”Finally, it may be that nationwide changes in vaccine policy, which affected both treatment and control counties, had differential impacts on treatment counties due to the priming of the advertising campaign. The key change in vaccine policy that occurred during our sample period was that children ages 5 to 11 became eligible for the vaccine on November 2. Information about this policy change was leaked slowly over the week preceding the change, with an official announcement from the CDC released on November 2 announcing the November 4 eligibility date. One possibility is therefore that the changing guidelines around childhood vaccination, and attention to these changes, can account for some of the reason that the treatment effect was larger near the end of the campaign.