Volatility and Heterogeneity of Vaccine Sentiments Means Continuous Monitoring is Needed When Measuring Message Effectiveness

Study Overview
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Brief Summary
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The success of vaccination programs often depends on the effectiveness of the vaccine messages, particularly during emergencies such as the COVID-19 pandemic. The current suboptimal uptake of COVID-19 vaccines across many parts of the world highlights the tremendous challenges in overcoming vaccine hesitancy and refusal even in the context of a world-devastating pandemic. The investigators conducted a randomized controlled trial in Hong Kong to evaluate the impact of seven vaccine messages on COVID-19 vaccine uptake (with the government slogan as the control). The participants included 127,000 individuals who googled COVID-19-related information during July-October 2021.

Detailed Description
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This study aims to evaluate the effectiveness of using the Google advertising platforms on influencing the uptake of COVID-19 vaccines in Hong Kong. When completed, the rich database compiled through this proposed study will provide increased insight into vaccine hesitancy in Hong Kong. Insights from the optimised online advertising trial can aid in providing crucial technical and theoretical support to the relevant health authorities for any potential evidence-based policy intervention in addressing vaccine hesitancy issues or the public's concerns towards vaccines in Hong Kong.

Official Title
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The Effect of Optimised Online Advertising on the Uptake of COVID-19 Vaccines in Hong Kong

Conditions
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Vaccine-Preventable Diseases, Vaccine Refusal

Intervention / Treatment
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* Behavioral: Google ads


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: General users of Google search in Hong Kong Exclusion Criteria: None
Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Health Services Research
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Government<br>Participants were shown with the government slogan for the COVID-19 vaccine campaign in 2021. This was the control arm. | Behavioral: Google ads<br>* Individuals who googled COVID-19 information in Hong Kong were randomized to see one of the seven ads and, if they clicked on the ads, the corresponding vaccine message on our website<br>|
| Experimental: Comparison<br>The ad emphasized that vaccine uptake in Hong Kong substantially lagged behind that in comparable populations such as Singapore and the UK. | Behavioral: Google ads<br>* Individuals who googled COVID-19 information in Hong Kong were randomized to see one of the seven ads and, if they clicked on the ads, the corresponding vaccine message on our website<br>|
| Experimental: Exemption<br>The ad emphasized that vaccinated people could be exempted from some disruptive control measures such as mandatory testing | Behavioral: Google ads<br>* Individuals who googled COVID-19 information in Hong Kong were randomized to see one of the seven ads and, if they clicked on the ads, the corresponding vaccine message on our website<br>|
| Experimental: Family<br>The ad prompted people to get vaccinated in order to protect their family. | Behavioral: Google ads<br>* Individuals who googled COVID-19 information in Hong Kong were randomized to see one of the seven ads and, if they clicked on the ads, the corresponding vaccine message on our website<br>|
| Experimental: Lottery<br>The ad prompted people to get vaccinated in order to be eligible for the numerous COVID-19 lotteries in Hong Kong | Behavioral: Google ads<br>* Individuals who googled COVID-19 information in Hong Kong were randomized to see one of the seven ads and, if they clicked on the ads, the corresponding vaccine message on our website<br>|
| Experimental: Mortality<br>The ad emphasized that COVID-19 has caused millions of deaths worldwide. | Behavioral: Google ads<br>* Individuals who googled COVID-19 information in Hong Kong were randomized to see one of the seven ads and, if they clicked on the ads, the corresponding vaccine message on our website<br>|
| Experimental: Reopen<br>The ad prompted people to get vaccinated to help Hong Kong reopen sooner. | Behavioral: Google ads<br>* Individuals who googled COVID-19 information in Hong Kong were randomized to see one of the seven ads and, if they clicked on the ads, the corresponding vaccine message on our website<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Number of bookings following each message delivery within 6 hours | The number of bookings made within X = 6 hours following each message delivery | 6 hours | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Number of bookings following each message delivery within 3 hours | The number of bookings made within X = 3 hours following each message delivery | 3 hours | 
| Number of bookings following each message delivery within 12 hours | The number of bookings made within X = 12 hours following each message delivery | 12 hours | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Vaccine hesitancy, Google ads, Vaccine messages, Vaccine confidence