VaccinationNCT07538349
Optimizing Weblinks Used in Digital Vaccination Invitations to Raise Trust and Booking Intention: Online Experiment 3
A study testing Improvement to the weblink included in the vaccination email invitation and Concealing the weblink included in vaccination email invitation in people with Vaccination, run by University of Essex at 1 site in United Kingdom.
Trial summary
This study investigates how the design of weblinks in digital vaccination invitation emails influences recipient trust and their willingness to book an appointment. In this study, investigators compare three different link formats: a control third-party link previously used by the NHS, and two experimental weblinks… Read more about this study
- Who is it for?
- Ages 18 years and olderHealthy volunteers can take part
- Conditions the study is for
- Vaccination
- What is being tested?
- Improvement to the weblink included in the vaccination email invitation and Concealing the weblink included in vaccination email invitation
- Type of treatment
- Vaccines, Lifestyle or therapy programme
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 4,014 participants
- Where
- 1 siteUnited Kingdom
- Study dates
- 1 Feb 2022to 2 Mar 2022
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- Healthy volunteers accepted
- Adult, Older adult
Who may be able to join
- Residency: Must be a resident of either the United Kingdom or the United States
Who cannot join
- Attention Failure: Participants who failed the designated attention check included within the survey will be excluded from the analysis
- Speeding: Participants who completed the study "too fast" - indicating a lack of meaningful engagement with the experimental stimuli - were filtered out
Trial locations and contacts
1 site in 1 country.
About this study
This study investigates how the design of weblinks in digital vaccination invitation emails influences recipient trust and their willingness to book an appointment. In this study, investigators compare three different link formats: a control third-party link previously used by the NHS, and two experimental weblinks: an improved version of the link, and a text embedded hyperlink.
The study tests primarily whether the two experimental weblinks will be perceived as more trustworthy and increase booking intention than the control weblink. Furthermore, the study examined whether the experimental weblinks are perceived to be more fluent (easier to read) and improve participants' ability to correctly identify the organisation (e.g., the NHS or a US pharmacy) that sent the hypothetical email.
Read more
To test these effects, investigators planned to gather data from 2,000 participants from the United Kingdom and 2,000 from the United States. They will be assigned to view one of the three hypothetical email versions. UK participants will see emails that appear to be from the NHS, while US participants see emails that appear to be from a local fictitious pharmacy. Due to US emails appearing to come from a fictitious pharmacy, investigators also expected that the benefit of correctly identifying the host organisation would be more pronounced in the United Kingdom than in the United States.
This research aims to provide evidence on how to design more effective and trustworthy digital health communications.
Read the detailed description
This randomised experimental study investigates how weblink design influenced the perceived trustworthiness of digital health communications. As digital invitations (e.g., emails and SMS) have become standard for public health initiatives such as vaccination programmes, the use of third-party or disfluent (hard-to-read) web links may inadvertently undermine trust.
Study Protocol and Intervention
Participants will be randomly allocated to one of three experimental conditions. In all conditions, participants will view a hypothetical email invitation for a COVID-19 booster vaccine. The content of the emails remains identical except for the format of the embedded booking link:
Control Condition: Features the "accurx" web link previously used by the National Health Service (NHS) in the UK.
Experimental Condition 1: Features an improved, transparent - "clear" - weblink that was designed to be easier to read and clearly identifies the host organisation (e.g., https://vaccine-booking.nhs.uk).
Experimental Condition 2: Features a text-embedded hyperlink.
To ensure relevance to the target populations, the stimuli are tailored to participants' countries of residence: UK participants see invitations appearing to come from the NHS, while US participants see slightly different versions of the email appearing to be sent by their local fictitious pharmacy. Unlike the UK, COVID-19 vaccination in the US was predominantly organised by local pharmacies.
Primary Hypotheses
The study is designed to test five primary hypotheses:
- The email containing the two experimental weblinks will be rated as significantly more trustworthy than the control "accurx" weblink.
- Participants will report being more likely to use the link to book a vaccine appointment based on the experimental weblinks than the control "accurx" web link.
- Participants will find the two experimental weblinks more fluent (easier to read) than the "accurx" control link.
- Participants will be more likely to correctly identify the organisation that hosts the link based on the two experimental weblinks than based on the "accurx" control web link.
- Identifying the organisation hosting the link will have a more beneficial effect on perception in the UK than in the US.
Measurement
Following the presentation of the stimulus, participants will rate the email on three 5-point Likert scales: trustworthiness (1: Very suspicious to 5: Very trustworthy), fluency (1: Very difficult to 5: Very easy), and booking intention (1: Very unlikely to 5: Very likely). Host identification is assessed via a multiple-choice question with four options: "the NHS", "your local pharmacy", "accurx", or "Not sure".
Investigators will gather data from 2,000 participants from the UK and 2,000 from the US. They will be invited to complete the study via an online platform. Participants who complete the study too fast or fail the attention check will be excluded.
This study will be conducted as part of a larger research project exploring the broader relationship between the content of health text messages and trust perception.
The study hypotheses, design, measures and analyses were preregistered before the start of data collection on a different platform (AsPredicted). This time stamped preregistration protocol is linked as a document in this registration.
- Conditions
- Vaccination
- Being tested
- Improvement to the weblink included in the vaccination email invitation, Concealing the weblink included in vaccination email invitation
- Keywords
- Trust, Digital Health Communications
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Improvement to the weblink included in the vaccination email invitationBehavioural
Participants were presented a hypothetical COVID-19 booster vaccination invitation email that included a booking weblink. The intervention involved improving the weblink included in the email to make it easier to read and facilitate the identification of the website host.
Concealing the weblink included in vaccination email invitationBehavioural
Participants were presented a hypothetical COVID-19 booster vaccination invitation email that included a booking weblink. The intervention involved concealing the weblink included in the email within text using a hyperlink (click HERE).
| Study group | Role | What they receive |
|---|---|---|
| Control: The weblink included in the email is cryptic: accurx.thirdparty+Host | No intervention | Participants were assigned to view a hypothetical vaccination invitation email containing the control weblink (UK participants: accurx.thirdparty.nhs.uk/r/aafwaczmd5; US participants: accurx.thirdparty.pharmacy.com/r/aafwaczmd5) |
| The web link in the email is a text-embedded 'Book here' weblink | Experimental | Participants assigned to this arm are shown a hypothetical COVID-19 booster vaccination invitation email in which the booking link is presented as a descriptive hyperlink - where the link is embedded in text (e.g., "Book your vaccine here"). Receives: Behavioral: Concealing the weblink included in vaccination email invitation |
| The web link in the email is a "clear" weblink: https://vaccine-booking+Host | Experimental | Participants were assigned to view a hypothetical email containing an improved version of the weblink that more clearly showed the website host and that was designed to be easier to read (UK participants: https://vaccine-booking.nhs.uk; US participants: https://vaccine-booking.pharmacy.com) Receives: Behavioral: Improvement to the weblink included in the vaccination email invitation |
What is being measured
The primary outcome is the main question the study is designed to answer.
Perceived Trustworthiness
Participants rated the perceived trustworthiness of the vaccination invitation email on a 5-point Likert scale, where 1 represents "Very suspicious", and 5 represents "Very trustworthy".
Measured: Immediately after the intervention
Booking Intention
Participants rated their likelihood of booking a vaccine appointment based on the email invitation using a 5-point Likert scale ranging from 1 ("Very unlikely") to 5 ("Very likely").
Measured: Immediately after the intervention
Secondary outcomes (2)
Ease of reading
Participants assessed the reading ease or fluency of the embedded weblink on a 5-point Likert scale, where 1 is "Very difficult", and 5 is "Very easy".
Measured: Immediately after the intervention
Host Identification
Participants were asked to identify the organisation that sent the communication by selecting one answer from a multiple-choice list of four options: the NHS, your local pharmacy, Accurx, or Unclear/I don't know
Measured: Immediately after the intervention
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted20 Apr 2026
- Study start1 Feb 2022
- Primary completion2 Mar 2022
- Study completion2 Mar 2022
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for VaccinationStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- This study follows a Parallel Assignment interventional model. Participants are randomly allocated to one of three independent groups to evaluate the impact of weblink design on trust and engagement with digital health communications.
- Masking
- Triple blind
- Who is masked
- Participant, Investigator, Outcomes assessor
- Enrolment
- 4,014 participants (actual)
Sponsor and investigators
- Lead sponsor
- University of Essex
- Sponsor type
- University, hospital or other
- Collaborators
- University of Southern California, Department of Health and Social Care, UK, Kingston University
- Responsible party
- Principal investigator, Marie Juanchich, University of Essex
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07538349
- Sponsor's protocol ID
- ETH 2122-0265 Expe3
- Other IDs
- CRUSA210009
- Status last verified
- Apr 2026
- First submitted
- 24 Mar 2026
- Last updated
- 20 Apr 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: Anonymised study data is shared on the Open Science Framework
Study at a glance
From the registry record, last updated by the sponsor on 20 Apr 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Optimizing Weblinks Used in Digital Vaccination Invitations to Raise Trust and Booking Intention: Online Experiment 3
- ClinicalTrials.gov ID
- NCT07538349
- Acronym / sponsor ID
- ETH 2122-0265 Expe3
- Conditions
- Vaccination
- Keywords
- Trust, Digital Health Communications
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 4,014 participants (actual)
- Lead sponsor
- University of EssexUniversity, hospital or other
- Collaborators
- University of Southern California, Department of Health and Social Care, UK, Kingston University
- Study start
- 1 Feb 2022 (actual)
- Primary completion
- 2 Mar 2022 (actual)
- Study completion
- 2 Mar 2022 (actual)
- First posted
- 20 Apr 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
This study investigates how the design of weblinks in digital vaccination invitation emails influences recipient trust and their willingness to book an appointment. In this study, investigators compare three different link formats: a control third-party link previously used by the NHS, and two experimental weblinks: an improved version of the link, and a text embedded hyperlink.
The study tests primarily whether the two experimental weblinks will be perceived as more trustworthy and increase booking intention than the control weblink. Furthermore, the study examined whether the experimental weblinks are perceived to be more fluent (easier to read) and improve participants' ability to correctly identify the organisation (e.g., the NHS or a US pharmacy) that sent the hypothetical email.
To test these effects, investigators planned to gather data from 2,000 participants from the United Kingdom and 2,000 from the United States. They will be assigned to view one of the three hypothetical email versions. UK participants will see emails that appear to be from the NHS, while US participants see emails that appear to be from a local fictitious pharmacy. Due to US emails appearing to come from a fictitious pharmacy, investigators also expected that the benefit of correctly identifying the host organisation would be more pronounced in the United Kingdom than in the United States.
This research aims to provide evidence on how to design more effective and trustworthy digital health communications.
Detailed description
This randomised experimental study investigates how weblink design influenced the perceived trustworthiness of digital health communications. As digital invitations (e.g., emails and SMS) have become standard for public health initiatives such as vaccination programmes, the use of third-party or disfluent (hard-to-read) web links may inadvertently undermine trust.
Study Protocol and Intervention
Participants will be randomly allocated to one of three experimental conditions. In all conditions, participants will view a hypothetical email invitation for a COVID-19 booster vaccine. The content of the emails remains identical except for the format of the embedded booking link:
Control Condition: Features the "accurx" web link previously used by the National Health Service (NHS) in the UK.
Experimental Condition 1: Features an improved, transparent - "clear" - weblink that was designed to be easier to read and clearly identifies the host organisation (e.g., https://vaccine-booking.nhs.uk).
Experimental Condition 2: Features a text-embedded hyperlink.
To ensure relevance to the target populations, the stimuli are tailored to participants' countries of residence: UK participants see invitations appearing to come from the NHS, while US participants see slightly different versions of the email appearing to be sent by their local fictitious pharmacy. Unlike the UK, COVID-19 vaccination in the US was predominantly organised by local pharmacies.
Primary Hypotheses
The study is designed to test five primary hypotheses:
- The email containing the two experimental weblinks will be rated as significantly more trustworthy than the control "accurx" weblink.
- Participants will report being more likely to use the link to book a vaccine appointment based on the experimental weblinks than the control "accurx" web link.
- Participants will find the two experimental weblinks more fluent (easier to read) than the "accurx" control link.
- Participants will be more likely to correctly identify the organisation that hosts the link based on the two experimental weblinks than based on the "accurx" control web link.
- Identifying the organisation hosting the link will have a more beneficial effect on perception in the UK than in the US.
Measurement
Following the presentation of the stimulus, participants will rate the email on three 5-point Likert scales: trustworthiness (1: Very suspicious to 5: Very trustworthy), fluency (1: Very difficult to 5: Very easy), and booking intention (1: Very unlikely to 5: Very likely). Host identification is assessed via a multiple-choice question with four options: "the NHS", "your local pharmacy", "accurx", or "Not sure".
Investigators will gather data from 2,000 participants from the UK and 2,000 from the US. They will be invited to complete the study via an online platform. Participants who complete the study too fast or fail the attention check will be excluded.
This study will be conducted as part of a larger research project exploring the broader relationship between the content of health text messages and trust perception.
The study hypotheses, design, measures and analyses were preregistered before the start of data collection on a different platform (AsPredicted). This time stamped preregistration protocol is linked as a document in this registration.
Study design
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Triple blind (participant, investigator, outcomes assessor)
- Number of arms
- 3
- Model description
- This study follows a Parallel Assignment interventional model. Participants are randomly allocated to one of three independent groups to evaluate the impact of weblink design on trust and engagement with digital health communications.
| Arm | Type | Receives |
|---|---|---|
| Control: The weblink included in the email is cryptic: accurx.thirdparty+Host | No intervention | –Participants were assigned to view a hypothetical vaccination invitation email containing the control weblink (UK participants: accurx.thirdparty.nhs.uk/r/aafwaczmd5; US participants: accurx.thirdparty.pharmacy.com/r/aafwaczmd5) |
| The web link in the email is a text-embedded 'Book here' weblink | Experimental | Behavioral: Concealing the weblink included in vaccination email invitationParticipants assigned to this arm are shown a hypothetical COVID-19 booster vaccination invitation email in which the booking link is presented as a descriptive hyperlink - where the link is embedded in text (e.g., "Book your vaccine here"). |
| The web link in the email is a "clear" weblink: https://vaccine-booking+Host | Experimental | Behavioral: Improvement to the weblink included in the vaccination email invitationParticipants were assigned to view a hypothetical email containing an improved version of the weblink that more clearly showed the website host and that was designed to be easier to read (UK participants: https://vaccine-booking.nhs.uk; US participants: https://vaccine-booking.pharmacy.com) |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (1 listed)
- Residency: Must be a resident of either the United Kingdom or the United States
Key exclusion criteria (2 listed)
- Attention Failure: Participants who failed the designated attention check included within the survey will be excluded from the analysis
- Speeding: Participants who completed the study "too fast" - indicating a lack of meaningful engagement with the experimental stimuli - were filtered out
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Improvement to the weblink included in the vaccination email invitationParticipants were presented a hypothetical COVID-19 booster vaccination invitation email that included a booking weblink. The intervention involved improving the weblink included in the email to make it easier to read and facilitate the identification of the website host. | Behavioural | The web link in the email is a "clear" weblink: https://vaccine-booking+Host |
| Concealing the weblink included in vaccination email invitationParticipants were presented a hypothetical COVID-19 booster vaccination invitation email that included a booking weblink. The intervention involved concealing the weblink included in the email within text using a hyperlink (click HERE). | Behavioural | The web link in the email is a text-embedded 'Book here' weblink |
Primary outcome
Perceived Trustworthiness
Time frame: Immediately after the intervention
Participants rated the perceived trustworthiness of the vaccination invitation email on a 5-point Likert scale, where 1 represents "Very suspicious", and 5 represents "Very trustworthy".
Booking Intention
Time frame: Immediately after the intervention
Participants rated their likelihood of booking a vaccine appointment based on the email invitation using a 5-point Likert scale ranging from 1 ("Very unlikely") to 5 ("Very likely").
2 secondary outcomes
Ease of reading
Time frame: Immediately after the intervention
Host Identification
Time frame: Immediately after the intervention
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 20 Apr 2026.
- Open Science Framework: Project Repository containing data, protocols, and materials.Link provided by the sponsor.
- Individual participant dataSharing planned: Yes. Anonymised study data is shared on the Open Science Framework
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
The record lists no contact. Use the official record to reach the sponsor.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Improvement to the weblink included in the vaccination email invitation and Concealing the weblink included in vaccination email invitation in people with Vaccination, run by University of Essex at 1 site in United Kingdom.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 1 inclusion and 2 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 20 Apr 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in United Kingdom. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Perceived Trustworthiness (time frame: Immediately after the intervention). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 20 Apr 2026.