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High COVID-19 vaccine uptake is crucial to containing the pandemic and reducing hospitalizations and deaths. Younger adults (aged 20-39 years) have demonstrated lower levels of vaccine uptake compared to older adults, while being more likely to transmit the virus due to a higher number of social contacts. Consequently, this age group has been identified by public health authorities as a key target for vaccine uptake. Previous research has demonstrated that altruistic messaging and motivation is associated with vaccine acceptance.
This study had 2 objectives: (1) to evaluate the within-group efficacy of an altruism-eliciting short, animated video intervention in increasing COVID-19 vaccination intentions amongst unvaccinated Canadian younger adults and (2) to examine the video’s efficacy compared to a text-based intervention focused exclusively on non-vaccine-related COVID-19 preventive health measures.
Using a web-based survey in a pre-post randomized control trial (RCT) design, we recruited Canadians aged 20-39 years who were not yet vaccinated against COVID-19 and randomized them in a 1:1 ratio to receive either the video intervention or an active text control. The video intervention was developed by our team in collaboration with a digital media company. The measurement of COVID-19 vaccination intentions before and after completing their assigned intervention was informed by the multistage Precaution Adoption Process Model (PAPM). The McNemar chi-square test was performed to evaluate within-group changes of vaccine intentions. Exact tests of symmetry using pairwise McNemar tests were applied to evaluate changes in multistaged intentions. Between-group vaccine intentions were assessed using the Pearson chi-square test postintervention.
Analyses were performed on 1373 participants (n=686, 50%, in the video arm, n=687, 50%, in the text arm). Within-group results for the video intervention arm showed that there was a significant change in the intention to receive the vaccine (
Although the video intervention was limited in its effect on those who had firmly decided not to vaccinate, our study demonstrates that prosocial and altruistic messages could increase COVID-19 vaccine uptake, especially when targeted to younger adults who are undecided or unengaged regarding vaccination. This might indicate that altruistic messaging provides a “push” for those who are tentative toward, or removed from, the decision to receive the vaccine. The results of our study could also be applied to more current COVID-19 vaccination recommendations (eg, booster shots) and for other vaccine-preventable diseases.
ClinicalTrials.gov NCT04960228; https://clinicaltrials.gov/ct2/show/NCT04960228
SARS-CoV-2 has caused the greatest pandemic of our lifetime. At the time of writing, the virus had infected 251 million people and killed over 5 million worldwide [
Following a rapid mobilization and development process, COVID-19 vaccination was introduced in late 2020, and widespread vaccination has since been encouraged for the general population. In Canada, vaccinating against COVID-19 has likely saved 476,000 lives [
Vaccine hesitancy, which refers to a set of attitudes and beliefs that may lead to delay or refusal of 1 or more vaccines despite their availability [
Although providing basic vaccine education to the population is critical, research has shown that correcting vaccine misinformation and refuting vaccine myths are largely ineffective in enhancing vaccine intentions [
A novel and promising approach is to develop interventions that elicit altruism, that is, intentional and voluntary action in which the primary goal is to increase the welfare of another person [
Considering the need to address hesitancy toward COVID-19 vaccination amongst younger adults, the aim of this study was to evaluate the efficacy of a short video intervention eliciting altruistic motives for vaccination. Understanding the effectiveness of altruism-based messaging could inform public health communications targeting COVID-19 vaccine uptake in this age group. The specific objectives were to estimate (1) pre- to postintervention change of COVID-19 vaccine intentions and (2) between-group COVID-19 vaccine intentions postintervention.
We used a 2-arm parallel randomized pre-post design. Participants in a web-based survey were randomly allocated in a 1:1 ratio to the video-based intervention or the active control arm consisting of a text-based intervention. The study was designed to detect a significant pre-post increase in COVID-19 vaccine intentions in the video intervention group and the superiority of the video intervention compared to the text intervention in eliciting pro-COVID-19 vaccine intentions. We used the Consolidated Standards of Reporting Trials (CONSORT) statement to report the results [
Participants from all Canadian provinces or territories who met following eligibility criteria were enrolled in the study: (1) not vaccinated for COVID-19, (2) age range of 20-39 years, (3) Canadian resident, and (4) willing to complete the survey in either English or French. To ensure a balanced participation in the study and informed by the Canadian Census data, we used quota sampling for the primary language spoken at home (80% Anglophones, 20% Francophones); biological sex (50% males, 50% females), annual total income before taxes of all members of the household before the pandemic (50% more than CA $75,000 [US $58,563.80], 50% less than CA $75,000), and population density (80% urban, 20% rural). During data collection (July 30-September 13, 2021), the daily incidence of COVID-19 was rising, signaling the emergence of the fourth pandemic wave in Canada that reached its peak mid-September, when about 4300 new daily cases were reported nationwide. In this period, about one-third of daily cases were reported in Canadians aged 20-39 years and the estimated daily COVID-19 incidence in this age group reached 1500 (35% of total daily cases) [
Data collection was carried out by Dynata, an international online market research company with experience in programing surveys and collecting data for universities and companies in various fields (eg, public health, politics). Dynata used a combination of recruitment methods (eg, its own website, direct emails, ads on social media) to recruit participants. At the beginning of the survey, we checked whether participants’ electronic device (the survey could be completed on a smartphone, computer, or tablet) had adequate video and sound capabilities to complete the survey. After providing electronic consent, participants deemed eligible to participate were randomly allocated to 1 of the 16 strata based on the 4 quota sampling criteria (ie, primary language, biological sex, income, and population density; see
After randomization, participants completed the remaining baseline sociodemographic questionnaire and provided their intentions to receive a COVID-19 vaccine. Then, they participated in the intervention (watched a short video eliciting altruism motives) or read a text related to general hygiene and preventive measures (active control group). All participants were prompted that attention check questions would follow. Those who did not correctly identify the names of the video characters were offered the possibility to watch the video a second time. Those who decided to watch the video again but still answered incorrectly were terminated. The video could be paused but not skipped or muted. Participants could not continue the survey until the video had been played entirely. In the active control arm, the sequence of information sections was randomized (to control for bias attributable to presentation order) and participants could neither skip sections nor progress to the next section until 10 seconds had elapsed to encourage careful reading. After each section, participants answered an attention check question asking them to identify a measure that was not mentioned in the section they had just read. Participants who answered all 3 attention check questions incorrectly were terminated.
Immediately after completing the intervention, we reassessed their intentions to receive a COVID-19 vaccine. Subsequently, participants answered additional questions (offered after the second assessment of vaccine intentions to avoid response bias), which included flu vaccination status, health care professional status, smoking history, and measures of altruism, empathy, and psychological distress. Only participants who provided complete survey data were retained in the final database. Participants were compensated by Dynata according to the reward system in which points are earned that can be later redeemed for company rewards (eg, Amazon, Starbucks).
Because mobile streaming is highly popular in our target age group [
The development of the intervention unfolded in following phases: First, we developed the script to focus on 3 characters with different COVID-19 vulnerability profiles (ie, John, 82 years old, vaccinated but at risk because of his age; Simon, 4 years old, not eligible for vaccination at the time of the study; and Marie, 32 years old, at risk of infection because of the immunosuppressive effects of chemotherapy). Subsequently, an initial storyboard was created by Akufen (a Montreal-based media design company), which was further refined and produced in video format. Adjustments were made based on the feedback received from 5 young adults (aged 20-39 years who had not yet received the COVID-19 vaccine) who viewed the video and participated in a focus group in June 2021. The final animated character video was 2 minutes 47 seconds in length. (Click to view the videos in English [
Consistent with the widespread use of public health messaging campaigns during the pandemic focusing on promoting preventive health behaviors, we decided to include an active instead of a placebo control group. We developed the text-based intervention by selecting
Baseline sociodemographics included continuous (ie, age) and categorical (province or territory, ethnicity, self-perceived visible minority [yes/no], gender identity, identification as a parent [yes/no], language spoken at home [English, French, other], postsecondary education attainment [yes/no], and income [CA $10,000 increments]) variables. Variables with a small cell count for some categories were recategorized. Provinces or territories were recategorized into Western, Central, and Eastern Canada. The 9 categories used by Statistics Canada to measure self-reported ethnic origins [
Based on the World Health Organization (WHO) Strategic Advisory Group of Experts on Immunization (SAGE) Working Group definition, vaccine hesitancy is considered on a continuum, which implies that using a binary (yes/no) would not allow for a precise, nuanced understanding of where individuals are in their vaccination decision-making process. Therefore, to measure COVID-19 vaccine intentions, we used a stage-based model of health decision-making, the Precaution Adoption Process Model (PAPM) [
Additional measures included following dichotomous (yes/no) variables: identification as a caregiver for an elderly person, identification as a health care professional, receiving a COVID-19 test, influence of religion on health decisions, and seasonal influenza vaccine uptake in the past 12 months. Smoking history was captured by 3 categories:
To calculate the required sample size for the within-participant change in vaccine hesitancy (ie, pre- to postintervention), we used survey data that showed that in January/February 2021, approximately 40% of Canadians aged 20-39 years were hesitant toward a COVID-19 vaccine (ie, don’t know yet or would refuse vaccination) [
Using data-cleaning techniques to identify careless responses is recommended for internet-based surveys as inattentive responses represent a threat to data validity [
For baseline sociodemographics, we calculated proportions and means (and SD) and used the Pearson chi-square test and the Welch 2-sample
Using the same analysis approach, we performed 2 subgroup analyses that included (1) all participants who answered the postintervention COVID-19 vaccine intentions question and participants who were initially removed during data cleaning (N=1654) and (2) all participants who were randomly allocated to the study groups and who answered the preintervention COVID-19 vaccine intentions question (N=2089, intention-to-treat approach). In addition, for both subgroups, we performed exploratory between-group analyses and operationalized the vaccine intention outcome in 2 different ways: (1) baseline (preintervention) vaccine intentions in the text group and postintervention intentions in the video group and (2) postintervention vaccine intentions in the text group and baseline intentions in the video group.
All statistical analyses were conducted using R v. 4.0.5 (R Core Team) [
The study was approved by the Research Ethics Board of the Integrated Health and Social Services University Network for West-Central Montreal (CIUSSS West-Central Montreal; Project ID #2021-2732).
Of 14,298 participants in the target age group who accessed the invitation to participate, 11,853 (82.9%) were assessed for eligibility, of whom 2097 (17.7%) were eligible (n=9578, 80.8%, were excluded because they were already vaccinated against COVID-19; n=174, 1.5%, did not meet other inclusion criteria; and n=4, 0.03%, dropped out) and were randomly allocated to the study arms: 1654 (78.9%) completed the postintervention assessment, and 1373 (65.5%; ie, 686, 50%, and 687, 50%, in the video and text intervention arms, respectively) were included in the analyses. See
CONSORT diagram. CONSORT: Consolidated Standards of Reporting Trials; PAPM: Precaution Adoption Process Model.
Data collection took place from July 30 to September 13, 2021. At about 5 weeks into data collection, daily recruitment significantly declined. The main barrier was the relative low proportion (about 22%) of eligible participants (ie, unvaccinated in the age group of 20-39 years). We conducted preliminary analyses using a total sample of 1346 participants (673, 50%, per group) and found that the number of observations ensured 80% power to detect a 5% pre-post change in vaccine intentions. Preliminary analyses showed a difference of about 2% as opposed to the expected between-group difference of 5% in vaccine intentions that we had anticipated. To reach a similar level of power would have required about 5500 participants per group (ie, an increase of 4200 from our initial sample calculations) to detect a statistically significant superiority of the video intervention. Reaching the new sample size target would not have been feasible due to time and budget considerations, and we decided to stop data collection.
The sample consisted of slightly more females (n=740, 53.9%), the mean age was 30.7 years, the majority used English as the primary language at home (n=1122, 81.7%), most reported a total gross household income in the year preceding the pandemic of less than CA $75,000 (US $58563.80, n=848, 61.8%), and most resided in an urban area (n=1067, 77.7%). None of the sociodemographic characteristics differed significantly between the study groups (see
Sociodemographic variables.
Characteristics | Total (N=1373) | Video group (N=686) | Text group (N=687) | Between-group differencea |
||
Age, mean (SD) | 30.7 (5.3) | 30.7 (5.4) | 30.7 (5.3) | .94 | ||
|
.98 | |||||
|
Male | 633 (46.1) | 316 (46.1) | 317 (46.1) | —b | |
|
Female | 740 (53.9) | 370 (53.9) | 370 (53.9) | — | |
|
.98 | |||||
|
Man | 626 (45.6) | 311 (45.3) | 315 (45.9) | — | |
|
Woman | 721 (52.5) | 362 (52.8) | 359 (52.3) | — | |
|
Gender diverse | 26 (1.9) | 13 (1.9) | 13 (0.4) | — | |
|
.08 | |||||
|
Western | 451 (32.8) | 225 (32.8) | 226 (32.9) | — | |
|
East | 105 (7.7) | 40 (5.8) | 65 (9.5) | — | |
|
Central | 813 (59.2) | 419 (61.1) | 394 (57.3) | — | |
|
Territories | 4 (0.3) | 2 (0.3) | 2 (0.3) | — | |
|
.43 | |||||
|
Rural | 306 (22.3) | 159 (23.2) | 147 (21.4) | — | |
|
Urban | 1067 (77.7) | 527 (76.8) | 540 (78.6) | — | |
|
.05 | |||||
|
Yes | 401 (29.2) | 217 (31.6) | 184 (26.8) | — | |
|
No | 972 (70.8) | 469 (68.4) | 503 (73.2) | — | |
|
.46 | |||||
|
English | 1122 (81.7) | 561 (81.8) | 561 (81.7) | — | |
|
French | 203 (14.8) | 105 (15.3) | 98 (14.2) | — | |
|
Other | 48 (3.5) | 20 (2.9) | 28 (4.1) | — | |
|
.63 | |||||
|
Yes | 858 (62.5) | 433 (63.1) | 425 (61.9) | — | |
|
No | 515 (37.5) | 253 (36.9) | 262 (38.1) | — | |
|
.56 | |||||
|
<19,999 (US $15,616.20)d | 149 (10.9) | 72 (10.5) | 77 (11.2) | — | |
|
20,000-39,999 (US $15,617-$31,233.20) | 253 (18.4) | 136 (19.8) | 117 (17.0) | — | |
|
40,000-59,999 (US $31,224-$46,850.20) | 227 (16.5) | 113 (16.5) | 114 (16.6) | — | |
|
60,000-79,999 (US $46,851-$62,467.20) | 217 (15.8) | 109 (15.9) | 108 (15.7) | — | |
|
80,000-99,999 (US $62,468-$78,084.20) | 188 (13.7) | 82 (12.0) | 106 (15.5) | — | |
|
>100,000 (US $78,085) | 288 (21.0) | 148 (21.5) | 140 (20.4) | — | |
|
Prefer not to answer | 51 (3.7) | 26 (3.8) | 25 (3.6) | — | |
|
.31 | |||||
|
North American Aboriginal | 107 (7.8) | 62 (9.0) | 45 (6.6) | — | |
|
Other North American | 637 (46.4) | 303 (44.2) | 334 (48.6) | — | |
|
European | 320 (23.3) | 160 (23.3) | 160 (23.3) | — | |
|
Asian | 98 (7.1) | 51 (7.4) | 47 (6.8) | — | |
|
Other | 211 (15.4) | 110 (16.0) | 101 (14.7) | — | |
|
.89 | |||||
|
Yes | 697 (50.8) | 347 (50.6) | 350 (50.9) | — | |
|
No | 676 (49.2) | 339 (49.4) | 337 (49.1) | — |
aChi-square or
b—: not applicable.
cOf 1373 participants, 848 (61.8%) and 525 (38.2%) reported an annual income before taxes of all members of the household before the pandemic of <CA $75,000 and ≥CA $75,000, respectively. The between-group difference in proportions was not significant (
dAn exchange rate of CA $1=US $0.78 has been applied.
Number of participants by PAPMa vaccine intention stage and intervention group at baseline and postintervention (N=1373).
Group | Unengaged | Undecided | Decided not | Decided to | Total | Between-group differenceb |
||
|
.65 | |||||||
|
Video | 74 (10.8) | 234 (34.1) | 292 (42.6) | 86 (12.5) | 686 (50.0) | —c | |
|
Text | 73 (10.6) | 255 (37.1) | 272 (39.6) | 87 (12.7) | 687 (50.0) | — | |
|
.64 | |||||||
|
Video | 54 (7.9) | 236 (34.4) | 277 (40.4) | 119 (17.3) | 686 (50.0) | — | |
|
Text | 47 (6.8) | 249 (36.2) | 285 (41.5) | 106 (15.4) | 687 (50.0) | — |
aPAPM: Precaution Adoption Process Model.
bChi-square test.
c—: not applicable.
In the video group, 43 (6.3%) participants changed from nonintenders at baseline (ie,
In the video group, we found a statistically significant change from
In the text group, we found a statistically significant change from
Postintervention, in the video group, 119 (17.3%) intended to receive the vaccine, 277 (40.4%) were decided against vaccination, 236 (34.4%) were undecided, and 54 (7.9%) reported being unengaged. In the text group, 106 (15.4%) intended to receive the vaccine, 285 (41.5%) were decided against vaccination, 249 (36.2%) were undecided, and 47 (6.8%) reported being unengaged. The between-group difference in vaccine intentions was not significant:
Results of additional subgroup analyses did not significantly differ from per protocol analyses (see
Results of exploratory analyses provided a signal that the video intervention was superior to the text intervention as the between-group difference in vaccine intentions was significant when using preintervention intentions in the text group and postintervention intentions in the video group (
PAPM stage transitions from T1 (baseline) to T2 (postintervention) in the video group (N=686). OR: odds ratio; PAPM: Precaution Adoption Process Model. Green arrows show significant transitions toward increased and red arrows toward decreased vaccination intentions. Gray arrows show nonsignificant transitions between stages..
PAPM stage transitions from T1 (baseline) to T2 (postintervention) in the text group (N=687). OR: odds ratio; PAPM: Precaution Adoption Process Model. Green arrows show significant transitions toward increased and red arrows toward decreased vaccination intentions. Gray arrows show nonsignificant transitions between stages.
To the best of our knowledge, this is the first population-based study that examined the effect of a video-based intervention eliciting prosocial (altruistic) motives on intentions to receive the COVID-19 vaccine in younger Canadian adults. We used a pre-post and randomized control trial (RCT) study design and recruited a national sample of unvaccinated 20-39-year-old Canadians who participated in a web-based survey between July and September 2021 in the context of the fourth COVID-19 pandemic wave. Our study had 2 specific objectives: (1) to estimate pre- to postintervention vaccine intention changes in participants who were randomly allocated to the video intervention or the text-based intervention that provided non-vaccine-related preventive health measures and (2) to estimate between-group vaccine intentions postintervention.
First, we found that the video intervention was effective in changing vaccine intentions and that 4.8% more participants intended to receive the vaccine postintervention. The size of the effect is consistent with results of the experimental study conducted by Li et al [
Using the theoretical PAPM to inform the measurement of vaccine intentions, we found a more nuanced understanding of pre- to postintervention change in vaccine intentions. Our results show that significantly more participants who watched the video changed toward a more advanced vaccine decision stage than participants in the text group. In both groups, we found that individuals who had not thought about receiving the vaccine (
Although pre-post analyses showed that the video intervention was effective in increasing vaccine intentions, between-group analyses did not confirm our hypothesis that watching the video would result in statistically significant higher intentions compared to reading non-vaccine-related information. Two factors may have contributed to this outcome: (1) The unexpected 2.7% increase in vaccine intentions in the active control group that reduced the hypothesized 5% between-group difference, and (2) the higher-than-expected vaccine hesitancy in our sample (which comprised ~40% “rigid hesitant” compared to ~10% found in 2 population-based studies conducted by our team that investigated HPV vaccine hesitancy [
Although achieving statistical significance for the between-group difference would have sent a strong signal related to the efficacy of the video intervention, we believe that our study can inform future research using interventions that elicit prosocial motives to increase COVID-19 vaccine intentions. For example, interventions could be adapted to include other forms of prosocial motivations, such as collectivism (the practice of prioritizing a group over individuals within the group) [
The main limitations derive from the premature termination of the study dictated by barriers in participant recruitment and by lower-than-anticipated COVID-19 vaccine hesitancy in the population of interest. As the target sample size was not reached, the sampling quotas used to match Canadian Census data deviated from the planned quotas and we included 3.9% more females, 2.3% more participants residing in rural areas, 5.2% less Francophones, and 11.8% less participants with annual total income before taxes of all members of the household before the pandemic of CA $75,000 (US $58,563.80). Although between-group differences were not significant, these differences in sociodemographics could impede the generalizability of the results to the Canadian population. The high proportion of participants who were in the
Using a web-survey and a pre-post and RCT study design, we showed that a brief video eliciting prosocial (altruism) motives increased COVID-19 vaccine intentions of Canadians aged 20-39 years, especially among those who were less engaged in the decision to vaccinate or were undecided. As web streaming is highly popular among younger adults, using short videos is an efficient modality to disseminate public health messages. The effect of the new intervention on increasing intentions was modest, but delivering messages that elicit prosocial motives to vaccinate to a large population could increase vaccine intentions in a significant number of individuals and assist in reaching vaccination targets and curbing the effect of the pandemic. As vaccine hesitancy is complex, it is likely that a multifaceted messaging approach that includes the benefits of vaccination for the community would be beneficial, especially in societies where individual values prevail over collective values. Our intervention could be adapted to align with the latest COVID-19 immunization recommendations (eg, boosters) or to increase vaccine intentions for other preventable diseases.
Strata.
Text intervention.
Sociodemographics subgroups.
Results tables.
Additional analyses.
CONSORT-eHEALTH checklist (V 1.6.1).
Consolidated Standards of Reporting Trials
human papillomavirus
6-item Kessler Psychological Distress Scale
odds ratio
prosocial tendencies measure
Precaution Adoption Process Model
randomized control trial
Toronto Empathy Questionnaire
This study was supported by a grant from the McGill Interdisciplinary Initiative in Infection and Immunity (MI4). The study was also partially supported by a supplementary grant from the Canadian Immunization Research Network (CIRN). OT is supported by the Canadian Institutes of Health Research (CIHR)-Frederick Banting and Charles Best Doctoral award (Award FBD-170837) outside the submitted work.
The authors warmly thank the media design company Akufen for producing and Laurie Blanchette for narrating the video, as well as our focus group participants.
Within the past 5 years, GZ has served as a consultant to Merck (regarding human papillomavirus [HPV] vaccination), Pfizer (regarding meningococcal vaccination), and Sanofi Pasteur (regarding adolescent vaccination). GZ also has served on advisory boards for Merck (regarding HPV vaccination) and Moderna (regarding COVID-19 vaccination). The other authors declare no conflicts of interest.