Nudging is a means of indirectly influencing human behavior by altering the choice architecture available to the decision maker. A recent study published in Nature examined the effectiveness of sending short messages (i.e. nudges) to people who were not vaccinated against COVID-19 immediately, a strategy that has proven effective in early stages of vaccine deployment.
Contrary to previous findings reported by Hengchen Dai and colleagues, the researchers found no evidence that this boost method increased vaccination in people who delayed their vaccination for at least five weeks.
Nathaniel Rabb and his colleagues tested whether text messages sent by the Rhode Island Department of Health (RIDOH) to facilitate vaccination in May and June 2021 would be effective in adults who were tested for COVID-19, but delayed vaccination. The outcome of interest was the vaccination status at the end of the measurement period, which fell one week after the last day of RIDOH messaging.
Participants had to receive one of eight possible messages (for example, “a vaccine awaits you”) or no message. Conditions varied with an emphasis on “safety, access, minimal likelihood of poor outcomes, reduced risk to one’s family, social norms, or a combination” of getting vaccinated. The study included a total of 142,428 participants and divided this population into three consecutive iterations.
Each group was then divided into a roughly equal number of participants per day. The first two iterations used an adaptive design in which message performance in the previous iteration predicted the likelihood of participants being assigned to that given message; it was an attempt to maximize vaccination.
The researchers found that nudges, in the form of messages, did not influence participants more or less than the control condition. This was the case when comparing each message type against the control, as well as an aggregated “any message” condition.
In other words, there is no evidence that this nudge strategy, which had proven to be an effective method of increasing vaccination during the early stages of vaccine rollout, is effective in people who remained unvaccinated for at least five weeks after becoming eligible. .
The authors write, “Public health officials, especially those avoiding or legally barred from mandates, may turn to this strategy to increase vaccination rates among the less enthusiastic, but will likely see minimal impact.”
They further speculate that some possible mechanisms that may explain the reduced efficacy of nudging include novelty of the vaccine when first introduced, oversaturation of this effect now, vaccine hesitancy, polarized discourse surrounding COVID-19 vaccines. , as well as varying social norms and general knowledge about vaccines.
The study, “Evidence from Statewide Vaccination RCT Shows Limitations of Nudges,” was authored by Nathaniel Rabb, Megan Swindal, David Glick, Jake Bowers, Anna Tomasulo, Zayid Oyelami, Kevin H. Wilson and David Yokum.