VaccinationNCT07532967
Optimizing Weblinks Used in Digital Vaccination Invitations to Raise Trust and Booking Intention: Online Experiment 2
A study testing Improved trust and engagement in people with Vaccination, run by University of Essex at 1 site in United Kingdom.
Trial summary
This study investigates how the design of web links in digital vaccination invitation emails affects recipient trust and their willingness to book an appointment. Researchers compare three different weblink formats: a control third-party link previously used by the NHS ("accurx"), and two experimental weblinks in… 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?
- Improved trust and engagement
- Type of treatment
- Vaccines, Lifestyle or therapy programme
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 1,203 participants
- Where
- 1 siteUnited Kingdom
- Study dates
- 13 Jan 2022to 23 Jan 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 web links in digital vaccination invitation emails affects recipient trust and their willingness to book an appointment. Researchers compare three different weblink formats: a control third-party link previously used by the NHS ("accurx"), and two experimental weblinks in which the original link is hidden: a shortened "bit.ly" link, and a text-embedded hyperlink.
The study primarily tests whether the two experimental weblinks will be perceived as more trustworthy and increase booking intention compared to the control weblink. Furthermore, the study examines whether the experimental weblinks is perceived to be more fluent (easier to read) and improves 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 will gather data from 600 participants from the United Kingdom and 600 from the United States. They will be randomly assigned to view one of the three hypothetical email versions. UK participants will see emails appearing to be from the NHS, while US participants will see emails from a fictitious pharmacy (Pharma-US). 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 influences 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 programs, 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 read a hypothetical email invitation for a COVID-19 booster vaccine. The content of the emails remains identical except for the format of the booking weblink included in the email:
Control Condition: Features the "accurx" web link (accurx.thirdparty.nhs.uk/r/aafwaczmd5) based on a third-party format used in official invitations from the UK's NHS.
Experimental Condition 1: (Concealed in shortened URL) features a shortened version of the link using a bit.ly domain.
Experimental Condition 2: (Concealed, text-embedded) shows the link presented as a descriptive hyperlink.
To ensure relevance to the target populations, participants will see a version of the hypothetical email tailored to their country of residence: UK participants will see invitations sent from the NHS, while US participants will see invitations from a fictitious pharmacy (Pharma-US). Unlike the UK, COVID-19 vaccination in the US was predominantly organised by local pharmacies.
Primary Hypotheses
The study was designed to test six 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 would 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.
- Trustworthiness, booking intention, host identification accuracy, and fluency would be positively correlated with each other.
- The effect of the link will be mediated by the identification of the host organisation and the fluency of the link.
Measurement
Following the presentation of the hypothetical email, 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 will be assessed via a multiple-choice question with four options: the NHS, Pharma-US, Accurx, or 'Not sure'.
The investigators will aim to gather data from 600 participants from the UK and 600 from the US. They will be invited to complete the study via an online platform. Participants who complete the study too fast or failed the attention check will be excluded.
This study will be conducted as part of a larger research project exploring the broader relationship between the trustworthiness of digital messages and national vaccination rates.
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
- Improved trust and engagement
- Keywords
- health communication, digital health, trust
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Improved trust and engagementBehavioural
The intervention involved presenting a hypothetical invitation to a COVID-19 booster vaccination via email. Participants were randomly allocated to view one of three versions of the invitation to evaluate how the specific design of the embedded weblink influences recipient trust and booking behaviour.
To ensure local relevance, the email stimulus was adapted based on the participant's country of residence: participants in the United Kingdom saw invitations that appeared to be from the NHS, while those in the United States saw invitations that appeared to be from a fictitious pharmacy, Pharma-US. Following the intervention, participants evaluated the email's trustworthiness, the link's fluency, and their own intention to book a vaccine appointment.
| Study group | Role | What they receive |
|---|---|---|
| Control | 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.pharmaus.com/r/aafwaczmd5) |
| Shortened URL | Experimental | Participants assigned to this arm are shown a hypothetical COVID-19 booster vaccination invitation email featuring a shortened URL using a bit.ly domain. To ensure local relevance, the email stimulus is tailored to the participant's geographic location: UK participants view an email appearing to be from the NHS, while US participants view an invitation appearing to be from a fictitious pharmacy, Pharma-US. Receives: Behavioral: Improved trust and engagement |
| Text-embedded link | Experimental | Participants assigned to this arm are shown a hypothetical COVID-19 booster vaccination invitation email where the booking link was presented as a descriptive hyperlink (e.g., "Book your vaccine here") rather than a visible URL. Following the study's geographic customisation, UK participants viewed an email stimulus that appeared to be from the NHS, while US participants viewed an invitation that appeared to be from Pharma-US. Receives: Behavioral: Improved trust and engagement |
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, Pharma-US, 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 posted16 Apr 2026
- Study start13 Jan 2022
- Primary completion23 Jan 2022
- Study completion23 Jan 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 how weblink design in digital health communications influences recipient trust and engagement with vaccine apppointment booking invitations.
- Masking
- Triple blind
- Who is masked
- Participant, Investigator, Outcomes assessor
- Enrolment
- 1,203 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
- NCT07532967
- Sponsor's protocol ID
- ETH 2122-0265 Expe2
- Other IDs
- CRUSA210009
- Status last verified
- Apr 2026
- First submitted
- 24 Mar 2026
- Last updated
- 16 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 16 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 2
- ClinicalTrials.gov ID
- NCT07532967
- Acronym / sponsor ID
- ETH 2122-0265 Expe2
- Conditions
- Vaccination
- Keywords
- health communication, digital health, trust
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 1,203 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
- 13 Jan 2022 (actual)
- Primary completion
- 23 Jan 2022 (actual)
- Study completion
- 23 Jan 2022 (actual)
- First posted
- 16 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 web links in digital vaccination invitation emails affects recipient trust and their willingness to book an appointment. Researchers compare three different weblink formats: a control third-party link previously used by the NHS ("accurx"), and two experimental weblinks in which the original link is hidden: a shortened "bit.ly" link, and a text-embedded hyperlink.
The study primarily tests whether the two experimental weblinks will be perceived as more trustworthy and increase booking intention compared to the control weblink. Furthermore, the study examines whether the experimental weblinks is perceived to be more fluent (easier to read) and improves 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 will gather data from 600 participants from the United Kingdom and 600 from the United States. They will be randomly assigned to view one of the three hypothetical email versions. UK participants will see emails appearing to be from the NHS, while US participants will see emails from a fictitious pharmacy (Pharma-US). 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 influences 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 programs, 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 read a hypothetical email invitation for a COVID-19 booster vaccine. The content of the emails remains identical except for the format of the booking weblink included in the email:
Control Condition: Features the "accurx" web link (accurx.thirdparty.nhs.uk/r/aafwaczmd5) based on a third-party format used in official invitations from the UK's NHS.
Experimental Condition 1: (Concealed in shortened URL) features a shortened version of the link using a bit.ly domain.
Experimental Condition 2: (Concealed, text-embedded) shows the link presented as a descriptive hyperlink.
To ensure relevance to the target populations, participants will see a version of the hypothetical email tailored to their country of residence: UK participants will see invitations sent from the NHS, while US participants will see invitations from a fictitious pharmacy (Pharma-US). Unlike the UK, COVID-19 vaccination in the US was predominantly organised by local pharmacies.
Primary Hypotheses
The study was designed to test six 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 would 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.
- Trustworthiness, booking intention, host identification accuracy, and fluency would be positively correlated with each other.
- The effect of the link will be mediated by the identification of the host organisation and the fluency of the link.
Measurement
Following the presentation of the hypothetical email, 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 will be assessed via a multiple-choice question with four options: the NHS, Pharma-US, Accurx, or 'Not sure'.
The investigators will aim to gather data from 600 participants from the UK and 600 from the US. They will be invited to complete the study via an online platform. Participants who complete the study too fast or failed the attention check will be excluded.
This study will be conducted as part of a larger research project exploring the broader relationship between the trustworthiness of digital messages and national vaccination rates.
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 how weblink design in digital health communications influences recipient trust and engagement with vaccine apppointment booking invitations.
| Arm | Type | Receives |
|---|---|---|
| Control | 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.pharmaus.com/r/aafwaczmd5) |
| Shortened URL | Experimental | Behavioral: Improved trust and engagementParticipants assigned to this arm are shown a hypothetical COVID-19 booster vaccination invitation email featuring a shortened URL using a bit.ly domain. To ensure local relevance, the email stimulus is tailored to the participant's geographic location: UK participants view an email appearing to be from the NHS, while US participants view an invitation appearing to be from a fictitious pharmacy, Pharma-US. |
| Text-embedded link | Experimental | Behavioral: Improved trust and engagementParticipants assigned to this arm are shown a hypothetical COVID-19 booster vaccination invitation email where the booking link was presented as a descriptive hyperlink (e.g., "Book your vaccine here") rather than a visible URL. Following the study's geographic customisation, UK participants viewed an email stimulus that appeared to be from the NHS, while US participants viewed an invitation that appeared to be from Pharma-US. |
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 |
|---|---|---|
| Improved trust and engagementThe intervention involved presenting a hypothetical invitation to a COVID-19 booster vaccination via email. Participants were randomly allocated to view one of three versions of the invitation to evaluate how the specific design of the embedded weblink influences recipient trust and booking behaviour. To ensure local relevance, the email stimulus was adapted based on the participant's country of residence: participants in the United Kingdom saw invitations that appeared to be from the NHS, while those in the United States saw invitations that appeared to be from a fictitious pharmacy, Pharma-US. Following the intervention, participants evaluated the email's trustworthiness, the link's fluency, and their own intention to book a vaccine appointment. | Behavioural | Shortened URL, Text-embedded link |
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 16 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 Improved trust and engagement 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 16 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 16 Apr 2026.