In Denmark, electronically delivered letters provided a “low-touch, inexpensive, and highly scalable” way of increasing the uptake of influenza vaccination among older adults, researchers report. Letters that focused on cardiovascular benefits and repeat reminder letters were the most effective of 9 form letters.
The nationwide, pragmatic, registry-based, cluster-randomized implementation trial during the 2022–23 influenza season included all Danish citizens aged 65 years or older or turning 65 years by Jan. 15, 2023. After excluding people in nursing homes and those with an exemption from the system, households were randomized to usual care or 1 of the 9 types of electronic letters.
Results showed the following based on a primary endpoint of receipt of influenza vaccination on or before Jan. 1, 2023: “We identified 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 964,870 (78.3%) participants across 691,820 households. Compared with usual care, influenza vaccination rates were higher in the group receiving an electronic letter highlighting potential cardiovascular benefits of vaccination (81.00% vs 80.12%; difference 0.89 percentage points [99.55% CI 0.29–1.48]; P <0.0001) and the group receiving repeated letters at randomisation and at day 14 (80.85% vs 80.12%; difference 0.73 percentage points [0.13–1.34]; P = 0.0006). These strategies improved vaccination rates across major subgroups including those with and without established cardiovascular disease. The cardiovascular gain-framed letter was particularly effective among participants who had not been vaccinated for influenza in the previous season (Pinteraction = 0.0002). A sensitivity analysis of all randomly assigned individuals accounting for within-household clustering yielded similar findings.”