medwireNews: Sending individuals with chronic diseases behaviorally informed electronic letters reminding them to have a free influenza vaccination significantly increases their uptake of the offer, show results from the Danish NUDGE-FLU-CHRONIC trial.
Six different types of letters were tested, a standard letter plus five that included a behaviorally informed “nudge.” Each type of letter improved vaccination uptake compared with no reminder letter, report the Danish researchers, with a repeated letter strategy having the most impact, followed by a letter outlining cardiovascular gains.
While annual influenza vaccination is recommended by worldwide guidelines for people with chronic diseases, “vaccination rates remain suboptimal, particularly among young and middle-aged adults,” note Tor Biering-Sørensen (Gentofte Hospitalsvej, Hellerup, Denmark) and colleagues in JAMA.
They found that behaviorally informed electronic letters increased the uptake of influenza vaccinations by 11 to 14 percentage points and could have “substantial public health implications” including beyond the Danish health system.
The investigators randomly assigned 299,881 individuals aged between 18 and 64 years to receive one of six letters delivered via the Danish governmental electronic letter system, Digital Post, or no letter (usual care). All the participants – just over half (53.2%) of whom were women – had at least one chronic disease known to be associated with an increased risk for adverse outcomes from influenza, including cardiovascular disease (20.6%), diabetes (14.5%), and lung disease (12.2%). Other conditions included cancer and hematologic, neurologic, and autoimmune diseases.
The intervention letters were based on a standard letter format outlining an individuals’ eligibility for free vaccination, a description of the risks associated with influenza, and instructions on how to book an appointment.
The five iterations included: the standard letter followed by a second (repeated) letter sent 10 days later; a letter with added text highlighting the cardiovascular gains of having the vaccine; a letter with added text highlighting the respiratory gains; an active choice/implementation intention prompt letter with added text on how to book an appointment including a link; and a loss-framing letter pointing out the implications of not getting vaccinated.
The letters were sent in September 2023, a week prior to the start of the 2023-24 government vaccination program.
Overall, more than a third (36.2%) of the study participants had an influenza vaccination on or before January 1, 2024, report the investigators. This compared with 31.8% in the preceding influenza season.
The 212,822 individuals who were sent any of the intervention letters had higher vaccination rates than the 87,059 individuals who were not sent a letter, at 39.6% versus 27.9%, giving a significant 11.7 percentage point difference, note Biering-Sørensen et al.
The intervention with the greatest impact was the repeated letter strategy, with 41.8% of recipients getting vaccinated – a significant 13.9 percentage point difference compared with those not receiving a letter.
Similarly, there was a significant 11.9 percentage point increase in vaccination rates with receipt of the cardiovascular gain-framing letter relative to usual care, with respective uptake rates of 39.8% and 27.9%.
Both sensitivity and post-hoc analyses gave comparable results favoring the repeated and cardiovascular gain-framing letter interventions, and the number of people who needed to be “nudged” to result in one additional vaccination was nine for any intervention letter and seven for the repeated letter strategy.
Despite the increased vaccination uptake rates after the intervention, the researchers observed no significant differences in clinical outcomes. Hospitalization for pneumonia or influenza occurred at the same 0.6% rate for those who received an intervention letter and those who did not, and the death rate was 0.7% in both groups.
“Our findings may provide a strong incentive for other countries, regions, or local entities to explore implementation of similar systems,” suggest Biering-Sørensen and co-authors.
They conclude: “Simple, scalable and cost-efficient electronic letter strategies may be utilized to encourage positive health behavior at a population level.”
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