As Canada records over 1,400,000 COVID-19 infections and 26,000 deaths, the need to stop the spread of the virus has become increasingly critical. Although younger individuals (aged 20-39) have lower hospitalisation and death rates than older adults, they have high rates of infection and may be less willing to accept a vaccine because they consider the disease to be less dangerous for themselves. It is of concern that around 30% of Canadians, especially younger adults, will not be willing to accept a COVID-19 vaccine. Vaccination will be the best method to control the pandemic in the future and protect those at higher risk of hospitalisation and death (e.g., elderly, those with chronic diseases). Therefore, achieving high rates of vaccination coverage among younger adults is very important in the long run to protect not only themselves but also others. For the experimental condition, the investigators will develop a brief video that will promote the vaccine's protection of others (altruism). For the control condition, the investigators will create an informational text on COVID-19 preventative health measures based on recommendations from the Public Health Agency of Canada. 2630 younger adults (aged 20 to 39) who have not yet received a dose of a COVID-19 vaccine will be recruited. To match Canadian demographics, participants will be recruited using the following quotas to reflect census data from Statistics Canada: 50% male and 50% female; 80% Anglophone and 20% Francophone; 80% urban and 20% rural; and 50% household income level less than $75,000 and 50% household income greater than $75,000. Half of the participants will be randomly assigned to watch the video, with the other half reading the text. In both groups, participants will complete a short online survey before and after viewing the video or reading the text. The goal is to assess the efficacy of the video on increasing younger adults' willingness to get a COVID-19 vaccine. The research team is partnering in this study with key agencies, e.g., Public Health Agency of Canada (PHAC), National Advisory Committee on Immunization (NACI), and the Institut National de Santé Publique du Québec (INSPQ) to help communicate the research findings to the general population.

The COVID-19 vaccine is the most effective way to arrest the pandemic. A high vaccine acceptance rate is needed to achieve community immunity; however, current COVID-19 vaccine acceptance rate remains low, particularly among younger Canadians. There have been no studies that have examined the impact of altruism on COVID-19 vaccine intentions using a video-based intervention. The investigators will examine the efficacy of a video intervention eliciting altruism on increasing younger Canadians' (ages 20-39) intentions to receive the COVID-19 vaccine using a randomized control trial. The results of this study will be used by public health authorities to increase COVID-19 vaccine uptake. There are two objectives of the study: 1) to assess the within-participant efficacy of the video intervention in increasing vaccine intentions; 2) to assess the between-participant efficacy of the video intervention in increasing vaccine intentions.

A 10-minute survey will be administered online to a sample of 2630 Canadian residents aged 20-39 years old and is available in both English and French. To calculate the required sample size for the within-participant change in vaccine hesitancy (i.e., pre-post video intervention) the investigators used survey data showing that approximately 40% of Canadians in this age group are COVID-19 vaccine hesitant i.e., don't know yet or would refuse vaccination. Estimating a 5% decrease of hesitancy in the video intervention group and a correlation of about 0.45 between paired observations, this group requires a sample size of 1315 pairs for detecting a 5% change of marginal proportions at a power of 80% and two-sided significance of 5%.

Participants will be randomized using a one-to-one ratio. Thus, 50% will be allocated to the video intervention and 50% to the text intervention. Using equal size groups will allow for the detection of a between group difference in vaccine intentions of 5-6% with a power of 0.8 and a two-sided significance of 5%. The total sample required for this study is 2630 participants i.e., 1315 in the video intervention group and 1315 in the text intervention group.

The investigators have contracted Dynata, the world's largest first-party data and insight platform, to conduct recruitment and host the survey. Dynata will send invitations in various forms (e.g., e-mail invitations, text messages and in-app alerts) to recruit eligible participants from their existing panel (individuals who have signed with Dynata and have expressed willingness to receive invitations to various appropriate surveys) until recruitment goals and quotas are met.

Stratified randomization will be used to allocate participants to either: 1) video intervention: viewing a 2-minute altruism-eliciting video, or 2) text intervention: reading a text containing information from the Public Health Agency of Canada about general health behaviours and public health recommendations concerning COVID-19, e.g., hand hygiene and respiratory etiquette, wearing non-medical masks, physical distancing, etc. Within each stratum (first language, sex, population density and household income), participants will be allocated randomly using a one-to-one ratio (one to the video intervention and one to the text intervention).

Participants will first be asked to answer several socio-demographic questions and will be asked to choose one of the following categories which describe their COVID-19 vaccine decision-making stage according to the Precaution Adoption Process Model (PAPM): unengaged, undecided, decided not to receive the vaccine, or decided to receive the vaccine. Subsequently, depending on their randomly assigned condition, participants will either be shown a 2-minute altruism-eliciting video, or a brief informational text. After viewing this content, to ensure that participants paid attention, participants will answer questions about the contents to check their understanding. Finally, participants will: 1) once again be asked to choose their COVID-19 vaccine decision-making stage; 2) be asked questions regarding previous vaccination history (e.g., seasonal influenza), lifestyle factors, self-perceived health status, personal history of SARS-CoV-2 infection, and preferred health-information channels; and 3) complete validated scales regarding altruism, empathy, personal distress, and vaccine hesitancy.

To test the outcome for objective 1, the McNemar's test will be used to compare paired (pre-post video intervention) proportions. To control for the potential effect of other factors (e.g., sociodemographics, previous influenza vaccination, lifestyle factors), the investigators will conduct multivariate analyses (General Estimating Equations) and estimate the associations between these factors and changes in COVID-19 vaccine intentions. For objective 2, the difference in proportions between the video intervention and text intervention will be analyzed using the Chi-square test. The investigators will test for significant differences in predictor variables between the two groups and use logistic regression analyses to estimate the associations between these variables and the outcome (vaccine acceptability). The significance level will be set at α = 0.05.

Inclusion Criteria:

• Residing within Canada and aged between 20 and 39 years.

Exclusion Criteria:

• Having received at least one dose of a COVID-19 vaccine

Consent form, data collection method, and organizational policy means only aggregated data will be shared with other researchers.

The number analyzed were those who completed the full survey, passed the in-survey attention checks, and were retained during post-hoc data cleaning methods (outlying survey response times, straight-lined responses).

Adverse data information was only collected during the administered survey (10-15 minutes length) within the recruitment period (July 30th, 2021 - September 13th, 2021).

Adverse event collection was provided to us by the survey fielding company, Dynata.

Several limitations presented themselves during study recruitment. COVID-19 vaccination rates amongst our target population (Canadian young adults) increased significantly, especially driven by vaccination mandates that were introduced in several provinces. This meant we were not able to reach our target sample size (2630 participants), preventing adequate power for calculations and the filling of our pre-specified sample quotas (limiting generalizability). Additional, we used self-reported data

All data collection and group assignment will be conducted by the survey company, Dynata. Participants' intervention group assignments will be unavailable to the investigator.