Optimizing Weblinks Used in Digital Vaccination Invitations to Raise Trust and Booking Intention: Online Experiment 3

NCT07538349 | Completed

• 2 other identifiers: ETH 2122-0265 Expe3CRUSA210009
• Study Type: interventional
• Target: 4,014
• Locations: 1 country
• Sites: 1

Brief 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: 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.

Conditions

Vaccination

Keywords

Trust; Digital Health Communications

Outcome Measures

Primary Outcomes (2)

• 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".

  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").

  Immediately after the intervention

Secondary Outcomes (2)

• Ease of reading

  Immediately after the intervention

• Host Identification

  Immediately after the intervention

Study Arms (3)

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").

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)

Behavioral: Improvement to the weblink included in the vaccination email invitation

Interventions

Improvement to the weblink included in the vaccination email invitation BEHAVIORAL

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.

The web link in the email is a "clear" weblink: https://vaccine-booking+Host

Concealing the weblink included in vaccination email invitation BEHAVIORAL

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).

The web link in the email is a text-embedded 'Book here' weblink

Eligibility Criteria

• Age: 18 Years+
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• Residency: Must be a resident of either the United Kingdom or the United States

You may not qualify if:

• 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

Sponsors & Collaborators

• University of Essex: lead
• University of Southern California: collaborator
• Department of Health and Social Care, UK: collaborator
• Kingston University: collaborator

Study Sites (1)

University of Essex

Colchester, Essex, CO4 3SQ, United Kingdom

Location

Related Links

• Open Science Framework: Project Repository containing data, protocols, and materials.

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: TRIPLE
• Who Masked: PARTICIPANT, INVESTIGATOR, OUTCOMES ASSESSOR
• Masking Details: This is a double-blind study in which participants were unaware of the specific experimental condition to which they had been assigned. Participants were randomly allocated to view only one of three possible versions of a hypothetical vaccination invitation email - featuring either a control link, a text-embedded hyperlink, or a transparent link - and were not informed of the existence or nature of the alternative stimuli. This masking ensures that their evaluations of trustworthiness, fluency, and booking intentions were not influenced by a direct comparison between the different link designs. As the study was conducted as an online survey via a fully automated platform, there was no direct interaction between the investigators and the participants during the intervention.
• Purpose: PREVENTION
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Professor of Psychology

Model Details: 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.

Study Record Dates

• First Submitted: March 24, 2026
• First Posted: April 20, 2026
• Study Start: February 1, 2022
• Primary Completion: March 2, 2022
• Study Completion: March 2, 2022
• Last Updated: April 20, 2026

Record last verified: 2026-04

Data Sharing

• IPD Sharing: Will share
• Shared Documents: STUDY PROTOCOL, SAP, ICF
• Time Frame: The data and the study protocol were shared while the main scientific output was under review for publication. After acceptance for publication, all content will be made publicly available.
• Access Criteria: The data and study protocol will be freely accessible to the public after the main scientific output is accepted for publication.

Locations

GB (1)