Limitations
INFLUENZA
This study has several limitations. Mobile app users were required to register for a CANImmunize account for the study. Registration allowed for influenza vaccine data to be uploaded to the users’ CANImmunize account; however, this additional step appeared to be a barrier to use as we saw low registration numbers. Study participants were randomized after study registration; hence, onsite personnel were not able to support participants randomized to the mobile app arm in activating their account, which may also have contributed to low account registration. However, this can be perceived as a strength as this provided more real-world effectiveness data of app usage as in a nonstudy setting, users would have to navigate this on their own without study staff assistance. The day 8 survey email served as a reminder to mobile app users to register their accounts if they had not yet done so, but it also provided a direct link to the web-based safety and usability surveys, which 94% of mobile app arm users who completed the survey chose to use, rather than registering for a mobile app account. As a result, we could not effectively evaluate user preference or experiences in the mobile app arm of the study. Another major limitation is that data about nonresponders were not collected, which could introduce risk for response bias, particularly since the response rate differed between the web-based notification arm (64%) and the mobile app arm (45%).