Optimizing Weblinks Used in Digital Vaccination Invitations to Raise Trust and Booking Intention: Online Experiment 2

NCT07532967 | Completed

• 2 other identifiers: ETH 2122-0265 Expe2CRUSA210009
• Study Type: interventional
• Target: 1,203
• Locations: 1 country
• Sites: 1

Brief 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 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.

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 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

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.

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.

Behavioral: Improved trust and engagement

Interventions

Improved trust and engagement BEHAVIORAL

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.

Shortened URL; Text-embedded 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 three possible versions of a hypothetical vaccination invitation email-featuring either a control link, a shortened URL, or a text-embedded hyperlink-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. 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 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.

Study Record Dates

• First Submitted: March 24, 2026
• First Posted: April 16, 2026
• Study Start: January 13, 2022
• Primary Completion: January 23, 2022
• Study Completion: January 23, 2022
• Last Updated: April 16, 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)