How text message reminders increase COVID-19 booster vaccine uptake: Two randomized controlled trials

Abstract

Background: Vaccines are effective and affordable health prevention measures to prevent vaccine-preventable diseases, but achieving sufficient vaccine uptake population-wide is challenging. In this work, we assess the impact of various text messages reminders on COVID-19 booster uptake and the extent to which the effect of messages holds over time. Additionally, we analyse whether people's self-reported vaccination intentions (measured in response to message prompts) corresponds to actual vaccine uptake and whether this relationship differs between message variants.

Methods: We performed two large sequential randomized controlled trials (RCTs) in the Netherlands (N = 140.973), with the design of RCT2 building on the findings of RCT1. We 1) analyzed the effect of various text messages on COVID-19 booster uptake; 2) assessed the extent to which these effects hold over time; and 3) tested whether a positive response to message prompts moderates the effect of message variant on vaccine uptake.

Results: First, the results of RCT1 demonstrate that text messages with an ownership frame ("your [vaccine] is ready for you") result in highest vaccine uptake (e.g., compared to no text message: OR = 1.28 [99 % CI 1.03-1.59]). RCT2 showed that text messages with an ownership frame and a specific date, time and location result in highest vaccine uptake (e.g., compared to no text message: OR = 2.10 [99 % CI 1.85-2.38]). Second, most message effects hold over a longer period of time (e.g., 'date, time, location' message versus no message: OR = 2.10 [99 % CI 1.85-2.38] on day 6 and OR = 1.36 [99 % CI 1.25-1.48] on day 50). Third, we find that participants who received our most effective text and replied that they will take the vaccine, are more inclined to actually take the vaccine compared to the message with broad opening hours OR = 2.86 [99 % CI 2.14-3.82].

Conclusion: Text message reminders are able to increase vaccine uptake. From the tested variations, messages with an ownership frame providing a specific date, time and location are most effective. Because text messages demonstrate no notable disadvantages, we advise Public Health authorities to include this effective intervention in their vaccination campaign strategies.

Keywords: COVID-19 vaccination; Intention-behaviour gap; Randomized controlled trial; Text message intervention.