Most countries in Europe are missing the WHO’s flu vaccine uptake target of 75% among older people. Around 47% of people aged 65 years and older are vaccinated in the EU, ranging from 9.6% in Poland to 77.5% in Denmark. Among younger adults, flu vaccine uptake is much lower – even in those with chronic conditions who face higher health risks if infected.
Experts have studied ways of increasing vaccine uptake, including through SMS reminders and electronic letters. Research shows that reminders can be effective, especially when the recipient can respond by booking an appointment for their vaccine. The message also matters.
To test which messages work best, Danish scientists enrolled 965,000 adults aged 65 years and older in a large study during flu season. The group included more than 264,000 people with cardiovascular disease. Known as the Nudge-Flu trial, it was one of the biggest ever studies of its kind. The results were published in The Lancet.
Participants were divided into ten groups. One, a control group, received their usual care from the health service. The other nine groups each received a different electronic letter through Denmark’s national digital communication system. The messages ranged from simple reminders that it was time to be vaccinated to messages that highlighted the benefits of vaccination.
Two ‘winning’ messages
The researchers found no clear improvement for several of these messages compared to usual care. However, there were two messages that made a real difference:
- The first highlighted the cardiovascular benefits of influenza vaccination, reminding recipients that vaccination could help protect not only against influenza but also against serious heart-related complications.
- The second was remarkably simple: sending a follow-up reminder two weeks after the initial message.
Both interventions increased vaccine uptake. Interestingly, they worked just as well in people with cardiovascular disease as in those without. The benefits were also consistent across people living with heart failure, ischaemic heart disease and atrial fibrillation.
The increases in uptake were relatively small but, rolled out across a large population, would translate into a large number of people signing up for their annual flu vaccine. The researchers ran a similar study (Nudge-Flu 2) the following year during flu season. That paper, published in Nature Medicine, confirmed that older people respond well to electronic ‘nudges’.
What about younger people?
Next, the researchers tested whether younger adults with chronic conditions would respond to electronic nudging. Almost 300,000 people aged 18 to 64, and living with a chronic condition, were included. The results were even stronger than those seen in older age groups.
The largest effect – 41.8% flu vaccine uptake vs 27.9% in usual care – was seen in those who received a reminder letter 10 days after their first invitation. Those who received a letter emphasising the potential cardiovascular benefits of vaccination also had higher vaccination rates: 39.8%.
The authors say the results suggest that ‘simple, scalable and cost-efficient electronic letter strategies’ could have substantial public health implications.
A follow-up study conducted one year later and published in NEJM Evidence, confirmed the earlier findings. Again, adults aged 18-64 living with chronic diseases responded well to messages highlighting potential cardiovascular benefits of flu vaccination: 39.1% uptake vs 24.1%.
‘Our four papers show the effect is consistent across seasons,’ says Prof Tor Biering-Sørensen, Founding Head of Center for Translational Cardiology and Pragmatic Randomized Trials. ‘Highlighting cardiovascular gain and sending reminder letters led to higher uptake, especially in younger groups where uptake is generally lower than in older people.’
A key insight from the Danish studies of electronic messages is that the public responds well to the prospect of avoiding cardiovascular events. Indeed, it seems that many recipients of these messages were motivated more by preserving the health of their heart than they were by avoiding flu.
The benefits of flu vaccination for cardiovascular health are in the spotlight in Europe, partly because vaccination is featured in the EU Safe Hearts Plan – an ambitious vision for improving heart health. The European Society for Cardiology (ESC) published a Clinical Consensus Statement last year on the role of vaccines in preventing heart attacks and exacerbating heart failure.
A gentle nudge
Behavioural science insights have often been used to improve vaccination rates, with reminders repeatedly shown to move the needle. Building on nudge theory – a behavioural economics concept describing how people make decisions – researchers have tested several approaches to prompting people to have their recommended vaccines.
- A 2021 paper by Dai H et al. showed that SMS reminders which included ‘ownership language’ (e.g. “A vaccine has been reserved for you”) increase vaccination by 3.6%.
- A large US study of 19 different text message ‘nudges’ found that sending an SMS to patients prior to a scheduled appointment was an effective way to encourage them to get vaccinated while at the doctor.
- Researchers in Pakistan showed a 30% increase in childhood vaccination using mobile audio messages. The trial demonstrated the effectiveness of behavioural nudges in a low-resource setting.
