Electronic 'Nudges' to Improve Influenza Vaccine Uptake May Be Less Effective in Patients with Diabetes


Analysis of the NUDGE-FLU study reveals electronic nudges designed to boost influenza vaccination were more effective in older adults without diabetes, highlighting the need for tailored approaches in diabetes populations.

Tor Biering-Sørensen, MD, MSc, MPH, PhD | Credit: Lundbeck Foundation

Tor Biering-Sørensen, MD, MSc, MPH, PhD
Credit: Lundbeck Foundation

An exploratory subgroup analysis of the landmark NUDGE-FLU is shedding light on the effects of electronically delivered nudges on influenza vaccination uptake among older adults according to diabetes status.

Hailed as the largest implementation trial ever conducted, results of the study, which included all adults aged 65 years or older in Denmark, suggest use of electronic letters designed to boost influenza vaccination may have a greater benefit in people without diabetes than those with diabetes.1

“We found that the overall beneficial effects of electronically delivered nudges in boosting influenza vaccination uptake based on repeated messaging and emphasizing cardiovascular benefits were present only in participants without diabetes, whereas the effect seemed reduced in those with diabetes,” wrote investigators.1

A nationwide, pragmatic, registry-based, randomized implementation trial, NUDGE FLU was conducted during the 2022-2023 influenza season in Denmark and included all adults aged 65 years or older or turning 65 years by January 15, 2023, with the exception of those in nursing homes or those who had an exemption from the mandatory governmental electronic letter system. Funded by Sanofi, trial protocol dictated households be randomized in a 9:1:1:1:1:1:1:1:1:1 to usual care or 1 of 9 different electronic letters leveraging different behavioral nudging concepts.2

The primary results of the NUDGE-FLU trial were debuted at the American College of Cardiology 2023 Scientific Sessions by principal investigator Tor Biering-Sørensen, MD, MSc, MPH, PhD, professor in the Center for Translational Cardiology and Pragmatic Randomized Trials at Copenhagen University Hospital. Results of the trial suggested influenza vaccination uptake was greater among those who received an electronic letter highlighting potential cardiovascular benefits of vaccination (81.00% vs 80.12%; difference, 0.89 percentage points [99.55% Confidence interval [CI], 0.29 to 1.48]; <.0001).2

A secondary analysis of the trial, the current study sought to explore the effect of electronic nudges on influenza vaccination uptake according to diabetes status. Of the 964,870 participants included in the NUDGE-FLU trial, 123,974 had diabetes at baseline.1

The cohort of patients with diabetes at baseline had a mean age of 74.1 (Standard Deviation [SD], 6.1) years, 60.7% were male, 81.7% had received an influenza vaccination in the previous session, and the median duration of diabetes was 9.4 (3.8 to 10.0) years. The cohort without diabetes at baseline had a mean age of 73.8 (SD, 6.3) years, 46.8% were male, and 76.9% had received an influenza vaccination in the previous season.1

When assessing vaccination uptake based on diabetes status in the trial, the investigators’ analysis suggested receipt of any electronic letter increased vaccine uptake among participants without diabetes (80.4% vs 80.0%; difference, 0.37 percentage points; 99.55% CI, 0.08 to 0.66; [Risk Ratio [RR], 1.005; 99.55% CI, 1.001 to 1.008]) relative to usual care, but this effect was not observed among participants with diabetes (83.4% vs 83.6%; difference, −0.19 percentage points; 99.55% CI, −0.89 to 0.51; [RR, 0.998; 99.55% CI, 0.989 to 1.006; P=.02 for interaction]).1

Investigators pointed out the apparent benefits of the cardiovascular benefits and repeated letter nudge concepts observed in the overall NUDGE-FLU trial were attenuated in participants with diabetes (cardiovascular gain letter: 83.7% vs 83.6%; difference, 0.04 percentage points; 99.55% CI, −1.52 to 1.60; repeated letter: 83.5% vs 83.6%; difference, −0.15 percentage points; 99.55% CI, −1.71 to 1.41) relative to their counterparts without diabetes (cardiovascular gain letter: 81.1% vs 80.0%; difference, 1.06 percentage points; 99.55% CI, 0.42 to 1.70; repeated letter: 80.9% vs 80.0%; difference, 0.87 percentage points; 99.55% CI, 0.22 to 1.52; P=.07 for interaction).1

“In this exploratory subgroup analysis of a randomized trial, electronic nudges improved influenza vaccination uptake in persons without diabetes, although there was no evidence of an effect in persons with diabetes,” investigators added.1 “More trials are needed to investigate the effect of digital nudges specifically tailored to individuals with diabetes.”


  1. Højbjerg Lassen MC, Johansen NK, Vaduganathan M, et al. Electronically Delivered Nudges to Increase Influenza Vaccination Uptake in Older Adults With Diabetes. JAMA Network Open. Published online December 20, 2023. doi: 10.1001/jamanetworkopen.2023.47630
  2. Campbell P. Linking flu vaccine to cardiovascular benefit could increase uptake in older adults. HCP Live. March 5, 2023. Accessed December 20, 2023. https://www.hcplive.com/view/linking-flu-vaccine-to-cardiovascular-benefit-could-increase-uptake-in-older-adults.
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