An analysis of the NUDGE-FLU (Nationwide Utilization of Danish Government Electronic letter system for increasing inFLUenza vaccine uptake) trial found that using digital reminders, or “electronic nudges,” improved influenza vaccine rates among older adults but did not improve clinical outcomes. 

The analysis is published in Annals of Internal Medicine.

Rates of influenza vaccination remain low globally, and scalable interventions are needed, according to a release from the American College of Physicians. Recently, the NUDGE-FLU trial found that letters designed using behavioral science principles and delivered through a governmental electronic letter system were effective in increasing influenza vaccination rates by one percentage point among older adults in Denmark. 

However, it is unknown if the increase in influenza vaccination rates was associated with improved clinical outcomes.

Researchers from the University of Copenhagen conducted a prespecified exploratory analysis of the NUDGE-FLU trial. Participants included 691,820 Danish adults aged 65 years and older during the 2022-2023 influenza season. The authors found that hospitalization for influenza or pneumonia occurred in 1% of participants for both groups, regardless of whether they received a digital reminder for vaccination. 

They also found that 13% of participants were hospitalized for any cause, with no significant difference between persons who did or did not receive a digital reminder. Similarly, the authors reported a similar rate of death among both groups. 

However, the authors note that they observed a 2.63% absolute increase in rates of influenza vaccination using the cardiovascular gain-framing letter from persons who had not been vaccinated during the previous influenza season.

“Modest increases in influenza vaccination rates seen with electronic nudges did not translate into observable improvements in clinical outcomes,” the researchers concluded in the study. “Seasonal influenza vaccination should remain strongly recommended.”

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