A large randomized controlled trial published in PNAS reports that the rate of coronavirus disease 2019 (COVID-19) booster vaccination can be increased considerably by sending one-time personal reminders rather than by offering small financial incentives.

Study: Reminders, but not monetary incentives, increase COVID-19 booster uptake. Image Credit: Andrew Angelov / Shutterstock.com

Background

COVID-19 booster vaccination is associated with significantly higher efficacy as compared to primary vaccination in terms of reducing COVID-19-related hospitalization and mortality. Despite life-saving health benefits, a low uptake of booster vaccines has been observed worldwide, mostly because of vaccine hesitancy.

As of January 2023, only 15% of the United States population received a booster dose. More strikingly, about 31% of the population has not even completed the COVID-19 primary vaccination.     

With declining vaccine efficacy and the emergence of novel viral variants, COVID-19 booster vaccination has become the primary focus of public health campaigns to control the pandemic. In an attempt to increase the rate of booster vaccination, public health agencies have adopted many strategies, including reminder messages and financial incentives.

In this randomized controlled trial, scientists investigate the impact of reminder messages and financial incentives on the COVID-19 booster vaccination rate.

Study design

This preregistered trial comprised 57,893 participants in a county health system in northern California. Reminder messages about getting COVID-19 booster vaccination within next two weeks were sent to the participants in early December 2022, both with and without a small incentive of $25 U.S. dollars (USD) for vaccination.

The study participants were randomly categorized into three groups. The first group received only reminder messages, the second group received reminder messages with additional information about financial incentives, and the third (control) group did not receive any reminders or financial incentives.

Important observations

The study population was ethnically diverse and mostly had low financial status. About 96% of the study participants had medical insurance coverage and only 4% was uninsured. On average, the participants received the first COVID-19 vaccine approximately 1.5 years prior to the date of receiving reminder messages.

The analysis of vaccination status of the participants revealed that both reminders and reminders combined with financial incentives increased the rate of booster vaccination as compared to the control condition of no reminders and no financial incentives.

As compared to the control group, booster vaccination rates increased by 32.5% and 31.3% in the reminder and reminder plus financial incentive groups, respectively. A comparatively lower vaccination rate in the reminder plus financial incentive group indicates that financial incentives do not have added benefits over reminders for increasing vaccine uptake.

Differential impacts of study interventions on vaccine uptake were observed based on age, language, message modality, and time since first vaccination. Reminder messages caused higher induction in vaccination rates in older adults aged 65 years or older as compared to that in adults 65 years and younger. Similarly, higher vaccination rates were observed for Spanish reminders as compared to English reminders, as well as for reminders sent through text messages as compared to e-mail reminders.

Spanish speakers and those who received text reminders had low vaccination rates at baseline. These observations indicate that study interventions would be particularly more effective for these two groups.

Study significance

A simple one-time reminder message can considerably increase COVID-19 booster vaccination rate, especially among high-risk groups, including adults 65 years and older. Notably, the study findings indicate that a small financial incentive does not increase vaccine uptake more than a simple reminder.

As observed in the study, every 76.9 text or 169.5 email messages led to an additional booster vaccination. Assuming a marginal cost of $0.10 USD for each message, scientists estimate that the cost for each additional booster vaccination would be $7.69 USD for text messages and $16.95 USD for email messages. This highlights the usefulness of a simple reminder message as a low-cost strategy to increase COVID-19 booster vaccination rates.

The current study includes participants from a single health system, which restricts the generalizability of the findings. Moreover, only one reminder was sent to the participants. Thus, more studies are needed to explore the impact of repeated reminders and tracking over a longer period of time.      

Written by

Dr. Sanchari Sinha Dutta

Dr. Sanchari Sinha Dutta is a science communicator who believes in spreading the power of science in every corner of the world. She has a Bachelor of Science (B.Sc.) degree and a Master's of Science (M.Sc.) in biology and human physiology. Following her Master's degree, Sanchari went on to study a Ph.D. in human physiology. She has authored more than 10 original research articles, all of which have been published in world renowned international journals.