Optimizing Weblinks Used in Digital Vaccination Invitations to Raise Trust and Booking Intention: Online Experiment 1

NCT07516600 | Completed

• 2 other identifiers: ETH 2122-0265 Expe1CRUSA210009
• Study Type: interventional
• Target: 1,226
• Locations: 1 country
• Sites: 1

Brief Summary

This study investigates whether the design of weblinks in digital vaccination invitations affects how much people trust the message and their willingness to book an appointment. Researchers compare a standard third-party weblink used by the NHS ("accurx.thirdparty.nhs.uk/r/aafwaczmd5") with an improved, more transparent weblink (https://vaccine-booking.nhs.uk). The study tests the hypothesis that the improved link will be perceived as more trustworthy and easier to read than the standard link. Further, the study tests whether participants would be more likely to correctly identify the sender and would be more willing to book a vaccine when shown the improved link. To test these effects, the investigators planned to conduct a study with 600 participants from the United Kingdom and 600 from the United States. Participants will be randomly assigned to view one of the two hypothetical email versions. UK participants will see an email that appears to be from the NHS. US participants will see an email from a fictitious pharmacy (Pharma-US).This research aims to provide evidence on how to design more trustworthy digital health communications when recipients are asked to click a weblink.

Conditions

Vaccination

Keywords

health communication; digital health; trust

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 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 intervention

Secondary Outcomes (2)

• Ease of reading

  Immediately after intervention

• Host Identification

  Immediately after intervention

Study Arms (2)

Control

NO INTERVENTION

Participants were assigned to view a vaccination invitation email containing the control weblink (UK participants: accurx.thirdparty.nhs.uk/r/aafwaczmd5; US participants: accurx.thirdparty.pharma-us.com/r/aafwaczmd5

Clear Link

EXPERIMENTAL

Participants were assigned to view an email containing an improved version of the link (UK participants: https://vaccine-booking.nhs.uk; US participants: https://vaccine-booking.pharma-us.com)

Behavioral: Improved trust and engagement

Interventions

Improved trust and engagement BEHAVIORAL

The intervention involves presenting a digital COVID-19 booster vaccination invitation via email. Participants are randomly allocated to view one of two versions of the invitation to evaluate the impact of the weblink design on trust and behaviour. To ensure local relevance, the email content is adapted based on the participant's country of residence; participants in the United Kingdom see invitations sent from the NHS, while those in the United States see invitations from Pharma-US

Clear Link

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 two possible versions of a hypothetical vaccination invitation email and were not informed of the existence or nature of the alternative stimulus. This ensures that their evaluations of trustworthiness, fluency, and booking intentions were not influenced by a direct comparison between the two link designs. As the study was conducted as an online survey via a fully automated platform, there is 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 followed a Parallel Assignment interventional model. Participants were randomly allocated to one of two independent groups to evaluate the impact of the weblink design on trust and engagement with digital health communication.

Study Record Dates

• First Submitted: March 24, 2026
• First Posted: April 8, 2026
• Study Start: January 3, 2022
• Primary Completion: January 10, 2022
• Study Completion: January 10, 2022
• Last Updated: April 8, 2026

Record last verified: 2026-03

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)