Electronic nudges to increase influenza vaccination uptake among patients with heart failure: A pre-specified analysis of the NUDGE-FLU trial

Vaccination Promotion Strategies in the Elderly: Systematic Review and Meta-Analysis

Background: The World Health Organization estimates that currently available vaccines prevent 2 to 3 million deaths worldwide each year. Preventing infectious diseases is an important public health priority to ensure healthy ageing and improve quality of life. This study's aim is to identify the best strategies to increase vaccination coverage in the elderly. Methods: A systematic review and meta-analysis were carried out, including a bibliographic search in the PubMed and Scopus databases. Studies in older people (60 years or older) on any type of intervention aimed at increasing vaccination coverage were included. The effect of the intervention was measured using the odds ratio (OR). Results: After applying the selection criteria, 20 studies were identified: 17 on influenza vaccines and 3 on other vaccines. Educational strategies obtained an OR = 1.63 (95% CI: 1.22-2.19, I2 = 0.59). Medical counselling obtained an OR = 3.13 (95% CI: 0.60-16.37, I2 = 0.95). Writing strategies obtained an OR = 1.14 (95% CI: 0.99-1.32, I2 = 0.93). Few studies reported the effect of free vaccination. Conclusions: The educational strategies proved to be more effective than the others in this study. Free vaccination and age may have important roles. Further studies are needed as research in this area remains limited.

Electronic Nudges to Increase Influenza Vaccination in Patients With Chronic Diseases: A Randomized Clinical Trial

Importance

Despite strong worldwide guideline recommendations, influenza vaccination rates remain suboptimal among young and middle-aged patients with chronic diseases. Effective scalable strategies to increase vaccination are needed.

Objective

To investigate whether electronically delivered letter-based nudges informed by behavioral science could increase influenza vaccination uptake among patients aged 18 to 64 years with chronic diseases.

Design, Setting, and Participants

Nationwide pragmatic registry-based randomized clinical implementation trial conducted between September 24, 2023, and May 31, 2024, enrolling all Danish citizens aged 18 to 64 years who met criteria for free-of-charge influenza vaccination in light of preexisting chronic disease. All trial data were sourced from nationwide administrative health registries.

Intervention

Randomized in 2.45:1:1:1:1:1:1 ratio to no letter (usual care) or 6 different behaviorally informed electronic letters.

Main Outcomes and Measures

The primary end point was receipt of influenza vaccination on or before January 1, 2024, assessed in 7 prespecified coprimary comparisons (all intervention groups pooled vs usual care and each individual intervention group vs usual care). Absolute risk difference in proportions and a crude relative risk were calculated for each comparison.

Results

A total of 299 881 participants (53.2% [159 454] female, median age, 52.0 [IQR, 39.8-59.0] years) were randomized. Compared with usual care, influenza vaccination rates were higher among those receiving any intervention letter (any intervention letter, 39.6% vs usual care, 27.9%; difference, 11.7 percentage points; 99.29% CI, 11.2-12.2 percentage points; P < .001). Each individual letter type significantly increased influenza vaccination with the largest effect sizes observed with a repeated letter sent 10 days after the initial letter (repeated letter, 41.8% vs usual care, 27.9%; difference, 13.9 percentage points; 99.29% CI, 13.1-14.7 percentage points; P < .001) and a letter emphasizing potential cardiovascular benefits of vaccination (cardiovascular gain, 39.8% vs usual care, 27.9%; difference, 11.9 percentage points; 99.29% CI, 11.1-12.7 percentage points; P < .001). Vaccination rates were improved across major subgroups.

Conclusions and Relevance

In a nationwide randomized clinical implementation trial, electronically delivered letter-based nudges markedly increased influenza vaccination compared with usual care among young and middle-aged patients with chronic diseases. The results of this study suggest that simple, scalable, and cost-efficient electronic letter strategies may have substantial public health implications.

Trial Registration

ClinicalTrials.gov Identifier: NCT06030739.

Rationale and design of NUDGE-FLU-CHRONIC and NUDGE-FLU-2: Two nationwide randomized trials of electronic nudges to increase influenza vaccination among patients with chronic diseases and older adults during the 2023/2024 influenza season

BACKGROUND

Yearly influenza vaccination is strongly recommended for older adults and patients with chronic diseases including cardiovascular disease (CVD); however, vaccination rates remain suboptimal, particularly among younger patients. Electronic letters incorporating behavioral nudges are highly scalable public health interventions which can potentially increase vaccination, but further research is needed to determine the most effective strategies and to assess effectiveness across different populations. The purpose of NUDGE-FLU-CHRONIC and NUDGE-FLU-2 are to evaluate the effectiveness of electronic nudges delivered via the Danish governmental electronic letter system in increasing influenza vaccination among patients with chronic diseases and older adults, respectively.

METHODS

Both trials are designed as pragmatic randomized implementation trials enrolling all Danish citizens in their respective target groups and conducted during the 2023/2024 influenza season. NUDGE-FLU-CHRONIC enrolls patients aged 18-64 years with chronic diseases. NUDGE-FLU-2 builds upon the NUDGE-FLU trial conducted in 2022/2023 and aims to expand the evidence by testing both previously successful and new nudges among adults ≥65 years during a subsequent influenza season. Persons with exemptions from the electronic letter system are excluded from both trials. In both trials, participants are randomized in a 2.45:1:1:1:1:1:1 ratio to either receive no electronic letter (usual care) or to receive one of 6 different behaviorally informed electronic letters. NUDGE-FLU-CHRONIC has randomized 299,881 participants with intervention letters delivered on September 24, 2023, while NUDGE-FLU-2 has randomized 881,373 participants and delivered intervention letters on September 13, 2023. Follow-up is currently ongoing. In both trials, the primary endpoint is receipt of influenza vaccination on or before January 1, 2024, and the secondary endpoint is time to vaccination. Clinical outcomes including respiratory and cardiovascular hospitalizations, all-cause hospitalization, and mortality are included as prespecified exploratory endpoints. Prespecified individual-level pooled analyses will be conducted across NUDGE-FLU, NUDGE-FLU-CHRONIC, and NUDGE-FLU-2.

DISCUSSION

NUDGE-FLU-CHRONIC is the first nationwide randomized trial of electronic nudges to increase influenza vaccination conducted among 18-64-year-old high-risk patients with chronic diseases. NUDGE-FLU-2 will provide further evidence on the effectiveness of electronic nudges among older adults ≥65 years. Collectively, the NUDGE-FLU trials will provide an extensive evidence base for future public health communications.

TRIAL REGISTRATION

NUDGE-FLU-CHRONIC: Clinicaltrials.gov: NCT06030739, registered September 11, 2023, https://clinicaltrials.gov/study/NCT06030739. NUDGE-FLU-2: Clinicaltrials.gov: NCT06030726, registered September 11, 2023, https://clinicaltrials.gov/study/NCT06030726.

Nudging a Nation - The Danish NUDGE Trial Concept

Danish NUDGE Trial ConceptRandomized encouragement trials randomize to an opportunity to receive treatment instead of to the treatment. Here, Johansen and colleagues combine randomized encouragement trials with several advantages inherent in the Danish health system.