Can nudges improve vaccination uptake effectively?

How much can nudges actually boost vaccination rates?

The answer depends on the population and the nudge design, but the largest and most rigorous studies show that nudges can produce meaningful, though often modest, increases. In a nationwide Danish trial of nearly 300,000 younger adults (18–64 years) with chronic diseases, sending any one of six behaviorally informed electronic letters raised influenza vaccination from 27.9% to 39.6%—a jump of 11.7 percentage points [1]. The most effective letter, a reminder sent a second time, pushed the rate to 41.8% [1]. That is a substantial public health gain from a simple, low-cost digital message. In contrast, the same research group ran an even larger trial in 881,373 adults aged 65 and older and found a much smaller effect: the pooled nudge letters raised vaccination from 76.02% to 76.32%, a difference of only 0.31 percentage points [3]. The reason is that older adults already had high baseline vaccination rates, leaving less room for improvement. So nudges work best when the starting vaccination rate is low.

Which types of nudges work best?

The evidence points to several specific nudge designs that consistently outperform others. Reminders are one of the most reliable: in the Danish trial of younger adults, a letter sent a second time (a repeated reminder) produced the largest effect, boosting vaccination by 13.9 percentage points over usual care [1]. Similarly, a trial in China found that a loss-framed narrative message (emphasizing what you stand to lose by not vaccinating) increased childhood influenza vaccination from 9.4% to 24.0%—a 2.5-fold relative increase [2]. Messages that highlight personal health benefits also work well: a letter emphasizing the cardiovascular benefits of flu vaccination increased uptake by 0.89 percentage points in older adults [5] and by 11.9 percentage points in younger adults with chronic disease [1]. Making vaccination easy is another powerful nudge: a study in Italy found that assigning people a pre-scheduled appointment (an opt-out default) increased COVID-19 vaccination by 3.2 percentage points compared to simply inviting them to book an appointment [10]. A meta-analysis of 16 randomized trials on COVID-19 vaccination confirmed that social norms, defaults, and salient reminders all had weak but positive effects, with social norms showing the largest relative increase (RR 2.04) [7].

Do nudges work equally well for everyone?

No, the effectiveness of nudges varies significantly across different groups. In the Danish trials, nudges were less effective in people with diabetes than in those without. For example, in older adults, the pooled nudge letters improved vaccination in those without diabetes (80.4% vs. 80.0%) but showed no evidence of effect in those with diabetes (83.4% vs. 83.6%) [6][9]. Similarly, in younger adults with chronic disease, the relative gain from nudges was smaller in those with diabetes than in those without [4]. This may be because people with diabetes already have higher baseline vaccination rates (83.5% vs. 80.2% in older adults) [6], leaving less room for improvement, or because they need different messaging. The same pattern appeared in people with heart failure: nudges worked equally well regardless of heart failure status, but the absolute gain was smaller because baseline rates were already high [8]. Importantly, nudges did not cause any unintended harm—for example, they did not reduce use of other recommended medications [8]. So while nudges are broadly effective, they are not a one-size-fits-all solution; tailoring them to specific populations may be needed.

About These Sources

This answer is built on 10 peer-reviewed studies — published from 2022 to 2025, 5 from 2024 or later, 7 in Q1 journals, collectively cited 169 times — selected as the most relevant from 15 studies that passed quality screening, drawn from 59 papers retrieved from a database of over 500 million.

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