‘Small but important effect’
In an accompanying editorial (Lancet. 2023 Mar 5. doi: 10.1016/S0140-6736(23)00453-1), Melissa Stockwell, MD, Columbia University, New York, writes, “The study by Johansen and colleagues highlights the small but still important effect of scalable, digital interventions across an entire at-risk population.”
A difference of 0.89% in the entire study population of over 960,000 adults age 65 years or older would be more than 8,500 additional adults protected, she notes. “That increase is important for a scalable intervention that has a low cost per letter.”
Moreover, “that the cardiovascular gain–framed messages worked best in those who had not been vaccinated in the previous season further highlights the potential impact on a more vaccine-hesitant population,” Dr. Stockwell notes.
However, with the mandatory government electronic notification system in Denmark, “notifications are sent via regular email and SMS message, and recipients log in through a portal or smartphone app to view the letter.” Similar studies in the United States that included this extra step of needing to sign in online have not been effective in older populations.
Another limitation is that the intervention may have a different effect in populations for which there is a digital divide between people with or without Internet access of sufficient data on their mobile phones.
First-of-its kind, nationwide pragmatic trial
The NUDGE-FLU protocol was previously published in the American Heart Journal. NUDGE-FLU is a first-of-its kind nationwide, pragmatic, registry-based, cluster-randomized implementation trial of electronically delivered nudges to increase influenza vaccination uptake, the researchers note.
They identified 964,870 individuals who were 65 years or older (or would turn 65 by Jan. 15, 2023) who lived in one of 691,820 households in Denmark.
This excluded individuals who lived in a nursing home or were exempt from the government’s mandatory electronic letter system that is used for official communications.
Households were randomly assigned 9:1:1:1:1:1:1:1:1:1 to receive usual care alone or to one of nine electronic letter strategies based on different behavioral science approaches to encourage influenza vaccination uptake:
- Standard electronic letter
- Standard electronic letter sent at randomization and again 14 days later (repeated letter)
- Depersonalized letter without the recipient’s name
- Gain-framing nudge (“Vaccinations help end pandemics, like COVID-19 and the flu. Protect yourself and your loved ones.”)
- Loss-framing nudge (“When too few people get vaccinated, pandemics from diseases like COVID-19 and the flu can spread and place you and your loved ones at risk.”)
- Collective-goal nudge (“78% of Danes 65 and above were vaccinated against influenza last year. Help us achieve an even higher goal this year.”)
- Active choice or implementation-intention prompt (“We encourage you to record your appointment time here.”)
- Cardiovascular gain–framing nudge (“In addition to its protection against influenza infection, influenza vaccination also seems to protect against cardiovascular disease such as heart attacks and heart failure.”)
- Expert-authority statement (“I recommend everyone over the age of 65 years to get vaccinated against influenza – Tyra Grove Krause, Executive Vice President, Statens Serum Institut.”)