London, 9 April 2025 – A small change in the wording of a text message led to an estimated 42,000 additional Covid vaccinations during the 2021 vaccine rollout in the UK. The findings are published today in the journal Nature Human Behaviour, documenting two studies which are among the largest individual-level randomized controlled trials ever conducted in the field of behavioural science.
Two nationwide randomised controlled trials (RCTs) investigated the response to specific text messages among 4 million adults aged 40-44 and 24-29. A text message telling people “you have reached the top of the queue” performed best against a control message and was subsequently rolled out as the standard reminder.
The research, conducted in 2021 by the Behavioural Insights Team (BIT), NHS England and NHS Improvement (NHSEI), and Public Health England (now DHSC/UKHSA), relates to text messages sent to members of the UK public to let them know that they were eligible for their COVID-19 vaccination in 2021.
As people were looking to get their first doses of the COVID-19 vaccine, BIT, NHSEI and PHE researchers led the first RCT trial to look at how they could boost takeup. The researchers developed eight versions of text messages sent from “NHSvaccines” and tested their effectiveness among people aged 40-44. Compared to the control message, the “top of the queue” message increased the vaccination rate by 0.38 percentage points, a statistically significant increase. None of the other messages that were tested delivered a statistically significant difference to the control group.
After that first study, a message telling people they were “top of queue” was rolled out nationally to the 4.7 million people in England aged 30-37 who were invited to receive their COVID-19 vaccination between May 18 and May 27 (in 2021).
The second RCT replicated the findings among younger people aged 24-29. In the study the researchers retained the three top performing messages from the previous trial and added two more. “Top of the queue” was again found to boost vaccine take-up alongside other messages including language relating to queuing. After the second trial the message was rolled out to an additional 2.5 million eligible adults.
Based on their observations the researchers estimate the “top of the queue” message led to around 42,000 additional first-dose COVID-19 vaccinations being received in these cohorts within 14 days of getting the text. In an editorial for Nature Human Behaviour, Dr Hannah Behrendt said that by understanding the “mental shortcuts and biases that influence our choices, researchers can craft messages that are more likely to resonate and encourage desired actions”.
The “top of the queue” message presumed that people already wanted to be vaccinated and framed the opportunity as a privilege. The message drew on literature which points to the effectiveness of emphasising scarcity and desirability to encourage people to take action.
The researchers suggest that further research can investigate the effectiveness of the “top of the queue” messaging in other contexts.
Dr Hannah Behrendt, lead author of the study, said:
“In England, text messages were the primary method used to invite the public to receive their COVID-19 vaccination. This provided a unique opportunity to test at scale whether tweaking these messages could increase vaccine uptake. Usually running a large-scale trial like this is slow and complex. In this case the need was urgent, time was short and we were working in a live policy environment. We found that a novel message – highlighting that people had reached the “top of the queue” – increased vaccine uptake. The urgent need for vaccine rollout facilitated rapid collaboration, allowing the most effective message to be implemented as soon as the results were available.”
Dr Giulia Tagliaferri, head of evaluation at BIT, said:
“This is the most socially impactful project I have ever worked on as an evaluator and behavioural scientist. Working shoulder to shoulder with NHSEI colleagues to run a live trial within the national roll-out of the vaccination campaign was terribly exciting. We managed to improve people’s lives and make real changes by embedding experimentation within established systems, in a real ‘test and learn’ spirit.”
In the first trial, the eight text messages were:
- a factual “Control” message about eligibility, a “Simple” version with different wording to make the message more accessible;
- a “Reserved” message which framed reminders as getting a vaccine that was already reserved for the patient;
- the “Top of queue” message that highlighted that participants were a priority for vaccination;
- the “Join the millions” version which relied on the social norm of getting the coronavirus vaccine in the UK;
- the “Convenience” version which sought to reassure participants that they could choose when and where to receive their vaccine;
- the “Protection against virus” version which highlighted the personal health benefits of getting vaccinated;
- the “Protect you and those close to you” version which emphasised both the personal and collective health benefits.
Ends
Notes to editors
- For more information on the analysis or to speak to one of the experts involved, please contact Kieran Lowe, Media Manager, on 020 7438 2576 or [email protected]. Spokespeople are available for broadcast interviews.
About BIT
BIT (the Behavioural Insights Team) is a global research and innovation consultancy which combines a deep understanding of human behaviour with evidence-led problem solving to improve people’s lives. BIT works with all levels of government, nonprofits and the private sector, applying behavioural science expertise with robust evaluation and data to help clients achieve their goals.
BIT has more than 200 staff, and operates from seven offices around the world. Together our staff provide unrivalled behavioural science expertise, amassed through the delivery of more than 1,700 projects across hundreds of countries.
BIT was established by the UK government in 2010. In 2014 BIT became an independent social purpose company, part owned by the Cabinet Office and the innovation charity Nesta. Since 2021 BIT has been entirely owned by Nesta and is part of the Nesta group.
For more information visit bi.team and follow BIT on LinkedIn or Bluesky.
