Evaluation of a behaviourally-informed email to increase flu vaccination uptake in local authority employees

Autumn / Winter 2022

Using behavioural science techniques to inform a flu vaccine invitation email can increase uptake of the flu vaccine; results of a randomised trial.

Dr Lesley Lewis and Dr Orla Dunn, Somerset County Council, Taunton.

Corresponding author: Lesley.Lewis@somerset.gov.uk


Influenza (the flu) causes serious illness and deaths every year, most notably within high-risk populations such as older-aged adults and those with chronic health conditions. In addition to the health impacts on individuals, cases of flu add additional pressures to the NHS due to increased hospitalisations, as well as affecting businesses due to staff sickness absences (Public Health England, 2020). For the benefit of both individuals and society, the flu vaccine is an effective method to mitigate against the harmful impacts of the flu and reduce transmission of the flu to vulnerable populations (Public Health England, 2020).

The NHS offers a flu vaccination programme each year, whereby certain populations are eligible to get a free flu vaccine. These populations typically include adults aged over 65 years, those in a clinical risk group, pregnant women, and frontline healthcare workers. Despite being offered a free vaccine, there are many reasons which prevent and facilitate an individual getting vaccinated. Beliefs and attitudes towards the flu vaccine play an important role, such as the perceived risk perception of getting the flu, the perceived severity of the flu, and the efficacy, safety and possible side effects of the vaccine (Schmid, Rauber, Betsch, Lidolt, & Denker, 2017; Prematunge, Corace, McCarthy, Nair, & Pugsley, 2012). In addition, the “where” and “who” may influence someone’s decision to get vaccinated, namely how easy it is to access a free vaccination and from whom the message comes, such as a trusted health professional or a family member (Schmid, Rauber, Betsch, Lidolt, & Denker, 2017; Prematunge, Corace, McCarthy, Nair, & Pugsley, 2012). Knowing these influences on behaviours can inform the development of interventions to increase uptake of the flu vaccine, as it can enable appropriate evidence-based techniques to be selected.

In 2021/22 Somerset County Council made the decision to offer a free flu vaccine to all employees not covered by the NHS, given the predicted flu levels and for staff welfare and business continuity. As part of this, a scheme was commissioned whereby employees could register for a flu vaccine voucher and subsequently book an appointment at a pharmacy convenient to them to receive their free flu vaccination. Employees would receive their invitation for a flu vaccine voucher via email, so to maximise uptake of the voucher scheme, the public health team sought to evaluate the effectiveness of three different email invitations.



A randomised trial was designed with three conditions: standard, BI-Short, and BI-Long (Appendix). Each of these conditions consisted of one email inviting employees to access a free flu vaccine voucher. The standard email was developed based on previous communications aimed at promoting the flu vaccine. The BI-Short and BI-Long emails were both behaviourally-informed, meaning that techniques to change behaviours were included to inform the layout and content, the former being a shorter version of the latter. Employees were randomly allocated to each condition, through a random number generator. The standard and BI-Short condition had 665 employees allocated each, while the BI-Long had 666 allocated.


A subsection of employees (n=1,996) under the age of 50 were randomly selected and sent an email invitation to register for a free flu vaccine voucher. A subsection was used, so that the results of the trial could inform the wider rollout of the voucher scheme, to optimise uptake. All employees in the trial received an email and exclusion criteria were applied for the analysis. Exclusion criteria included employees on long-term sick leave or had left the organisation. Additionally, employees were asked to make contact if they had already received a flu vaccine, and those that had were excluded from the analysis.


The intervention was developed with an approach in line with the Behaviour Change Wheel (Michie, van Stralen, & West, 2011), namely identify the target behaviour, understand the behaviour, and select evidence-based techniques to inform the intervention.

Identify the target behaviour

Three behaviours were identified 1) register for a voucher, 2) book a flu vaccine appointment, and 3) attend flu vaccine appointment. While the focus of the emails were to influence uptake of the vaccine, it was recognised that the first behaviour ‘register for a voucher’ was the key first step in making this happen. The emails, however targeted both voucher registration and vaccine uptake.

Understand the behaviour

Due to timescales, a brief literature review was conducted to highlight key barriers and facilitators of getting the flu vaccine, which could influence voucher registration and vaccine uptake. The findings were mapped to the COM-B model (Michie, van Stralen, & West, 2011), which specifies that capability, opportunity, and motivation are required in order to perform a behaviour. In brief, capability consists of psychological capability (cognitive skills) and physical capability (physical skills), opportunity consists of physical opportunity (environment and resources) and social opportunity (influence of others), and motivation consists of reflective motivation (beliefs and attitudes) and automatic motivation (habits and emotions). From the results, it was decided to focus on aspects of psychological capability and reflective motivation as these were seen as most influential and amenable to change within the intervention.

Select evidence-based techniques

Behaviour Change Techniques (BCTs) were selected (Table 1), which are the building blocks of interventions (Michie, et al., 2013). Although similar BCTs were used across interventions, the content of them varied slightly. For example, the standard email was almost double in length compared to the BI-Short email, which contained less information about the health consequences of catching the flu (Table 1).

One of the key differences between the BI-Short and BI-Long email compared to the standard email was in the layout. The “EAST” framework (Service, et al., 2012) was used to help inform this, which specifies that behaviours are influenced by making them easy, attractive, social, and timely. The “easy” concept was capitalised on by making it as easy as possible for employees to understand what they had to do. The instructions for voucher registration were therefore put into a box and labelled with clear steps to follow. In comparison, in the standard email, the instructions were in the fifth paragraph and written out as four sentences. Additionally, some of the content was informed by the concepts of “attractive”, “social” and “timely”. The word “free” was put in bold in the BI-Short and BI-Long emails to make the “attractiveness” salient, it was stated that the Chief Executive and Director of Public Health would be booking their appointment as soon as they could (social), and participants were asked to plan five minutes in their day to book an appointment (timely). These techniques were not included in the standard condition.

Table 1. Techniques used within the intervention conditions.


In total, 1,996 employees were sent an email inviting them to register for a free flu vaccine voucher. Participants were excluded if a system based undelivered reply was received or if an automatic reply indicating long term absence of more than 3 months was received, e.g. stated maternity leave, long term sickness sign off or end of employment (n=134). Participants were also asked to reply if they had already received a vaccination either via the NHS or having paid privately; 30 participants were excluded for this reason. After exclusion criteria were applied, 1,832 employees remained in the analysis (Figure 1).

Figure 1. Number of participants across intervention conditions.

Figure 2 shows the voucher registration and flu vaccine uptake across intervention conditions. The BI-Short condition resulted in the highest percentage of voucher registration and vaccine uptake, followed by BI-Long. The standard condition had lowest uptake for voucher and vaccine. In terms of vaccine uptake, the BI-Short and BI-Long conditions had an equal percentage uptake, which was higher than the standard condition. The conversion rate of registered vouchers to vouchers being used (i.e. vaccine uptake), was highest for BI-Long (57.3%) and lowest for the standard condition (49.1%).

Figure 2. Percentage uptake across intervention conditions.

A Chi-Square Test of Independence was conducted to test any significant differences between the conditions on taking action after receiving the email (flu voucher registration or vaccine uptake combined). This indicated that there was not a significant difference, though the p-value was approaching significance (χ2(2) = 6.008, p = 0.050). Additionally, differences between those who had the flu vaccine and those who did not were not significant across the different conditions (χ2(2) = 5.445, p = 0.066).


Although the results were not statistically significant, the trial conducted indicated that behaviourally-informed emails resulted in greater uptake of flu vaccine voucher registration and flu vaccine uptake compared to a standard email. It is thought that one of the main reasons for this was to do with the layout of instructions for registering a voucher and activating it, as this was one of the key differences between the behaviourally-informed emails and the standard email. In the behaviourally-informed emails, these were extremely clear and made salient at the start of the email. Therefore, using the “EAST” framework, specifically making instructions on how to perform the behaviour as easy as possible for individuals, may be useful for future invitations. Having clear steps and containing brief text with key information at the start of a document is recognised as important for achieving effective communication (Center for Applied Behavioral Science, 2020).

The content of the emails may have influenced results, which were only slightly different across the conditions. All three conditions included the BCTs, “Information about health consequences” and “Information about social and environmental consequences”, however they were applied in different ways; the BI-Short email contained the least amount of information about health consequences, while the BI-Long contained similar content as the standard email but was presented in different ways, for example with different section headings. This highlights the importance of detailing how BCTs were used within an intervention, as one BCT can be implemented in different ways. It may be that other BCTs could have been used to have more differentiation between the conditions, which may have contributed to significant results, though it would have been less clear what specific components of the BCTs were effective.

Research on topics other than flu have trialled amending letters to increase desired behaviours, such as increasing uptake of health checks and reducing antimicrobial prescribing. These have included testing loss-framed messages and gain-framed messages (Gold, Durlik, Sanders, Thompson, & Chadborn, 2019), and utilising social-norms (Hallsworth, et al., 2016) and commitment (NHS, 2021). While some of these have also shortened the amount of text within invitation letters, as in the BI-Short condition, other techniques may be considered for use in future work to increase flu vaccine uptake. Previous research to encourage flu vaccine uptake, specifically, has investigated the effectiveness of text messages (Milkman et al., 2021). While this was targeted towards patients getting a flu vaccine at a doctor’s surgery, the most effective message indicated that a flu vaccine had been reserved for the patient. This technique could be used within this context, in terms of specifying that a flu voucher has been reserved.

There are several limitations within this trial, with the main one being that only one email was delivered. Reminder emails were not sent, however this could be a future focus, providing a reminder to those who had registered for a voucher but had not had the vaccine. However, it was still interesting that there was a higher (albeit non-significant) uptake of the vaccine in both of the behaviourally-informed conditions despite an absence of a reminder, with the conversion rate of voucher registration to vaccine uptake being highest in the BI-Long condition.


The findings from this trial suggest that small changes to emails can result in slightly improved uptake in voucher registration and vaccine uptake, with the latter increasing by almost five percentage points. The results were used to inform the wider rollout of the flu vaccine voucher scheme across the local authority, however future work could focus on the application of different BCTs across letters.


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  1. Behaviourally-informed email template – Standard Email
  2. Behaviourally-informed email template – Short Email
  3. Behaviourally-informed email template – Long Email