Key Points
- Despite the proven benefits of annual influenza (flu) vaccination among patients with cardiovascular disease (CVD), uptake remains suboptimal.
- The NUDGE-FLU implementation trial randomized all Danish citizens ages 65 and older with access to the official Danish electronic letter system to usual care (no letter) or one of 9 active arms utilizing electronic letters (E-letter) with a different nudging strategy for flu vaccination. One of the nudges specifically mentioned the potential cardio benefits of the vaccine. The primary endpoint was receipt of the flu vaccine.
- Electronically delivered letters highlighting potential cardiovascular benefits of influenza vaccination or sent again as a reminder significantly increased vaccination uptake across Denmark, and they especially effective in those who had not been vaccinated the previous season.
- This is likely one of the largest randomized implementation trials in history; while the magnitude of effect was not very large, this study demonstrated that an automated, inexpensive and scalable intervention can help make modest but real gains in public health.
Patients with cardiovascular disease are at particularly high risk for adverse outcomes following influenza infection. Vaccination against influenza has been shown to reduce both the rates of infection and its complications.
The Danish healthcare system is unique in that there is a mandatory governmental electronic letter system that can be used to promptly and reliably deliver information to residents. Flu vaccination is free, and the vaccination rates approach 78% among those 65 and older.
On March 5, 2023, Dr. Niklas Dyrby Johansen presented the results of the NUDGE-FLU Trial. The accompanying manuscript, Electronic Nudges to Increase Influenza Vaccination Uptake in Denmark: A Nationwide, Pragmatic, Registry-based, Randomized Implementation Trial, will be published in the Lancet.1
In this trial, all Danish citizens age 65 and older were included. Those residing in nursing homes and those who opted out of the electronic system and preferred physical letters only were excluded. They were randomized in a 9:1:1:1:1:1:1:1:1:1 fashion at the household level to usual care with no letter or to one of 9 intervention arms. One intervention arm received a standard electronic letter, one intervention arm received a standard letter twice, and the other 7 arms had a letter designed based on specific behavioral science concept to “nudge” the patient towards vaccination. One of these letters specifically mentioned the cardiovascular (CV) benefits of flu vaccination, denoted as the “CV gain frame” letter. While not blinded, patients were not aware the letters were part of a trial, and there was no contact between investigators and participants.
A total of 1 232 938 individuals aged 65 years or older in Denmark and excluded 56 436 (4·6%) individuals living in nursing homes and 211 632 (17·2%) with an exemption from the electronic letter system. We randomly assigned 964870 (78·3%) participants across 691820 households.
The arms were well balanced, with 77% of patients in each arm being vaccinated in prior season and 28% with chronic cardiovascular disease. They found that of all the arms, two were associated with higher flu vaccination uptake compared to usual care. The first was the arm that received the standard electronic letter twice, once at randomization and again 14 days later (difference in vaccination +0.73 percentage points, RR 1.0009, p=0.0006). The other was the arm with the “CV gain frame” letter (difference in vaccination of +0.89 percentage points, RR 1.011, p<0.0001). The number of letters needed to result in one additional vaccination was 137 in the repeated letter group and 112 in the “CV gain frame” letter group. The magnitude of benefit of “CV gain frame” letter was significantly higher among those who had not been vaccinated the previous season. The effect of these two letter types were consistent across pre-specified subgroups.
In what is likely the largest randomized cardiovascular implementation trial to date, two electronic letter strategies were associated with increased influenza vaccine uptake. “Communicating potential CV benefits of vaccination was particularly effective in persons without influenza vaccination in prior seasons,” highlighted Dr. Johansen. Therefore, this specific type of behavioral nudge might be especially helpful in targeting those with vaccine hesitance. The incremental benefit was modest, but the costs and effort of the intervention were low and it is readily scalable. Across a large cohort, small percentage differences can result in large absolute numbers. “The results may have important implications when translated to a population level,” Dr. Johansen concluded.
References
- Johansen ND, Vaduganathan M, Bhatt AS, et al. Articles Electronic nudges to increase influenza vaccination uptake in Denmark : a nationwide , pragmatic , registry-based , randomised implementation trial. 2023;6736(23):1–12.
