Transition to endemic: acceptance of additional COVID-19 vaccine doses among Canadian adults in a national cross-sectional survey

COVID-19 vaccines have proven to be highly effective at limiting morbidity and mortality associated with SARS-CoV-2 infection [1]. However, the ongoing emergence of new SARS-CoV-2 variants of concern, and waning immunity among already vaccinated individuals, have highlighted the need for additional vaccine doses to boost population immunity [2‐4]. In settings where primary series coverage exceeds 50%, booster dose programs may be a more effective strategy for limiting population-wide negative effects of COVID-19 disease than improving primary series uptake among the unvaccinated [5]. This has led some countries, including Canada [6, 7], to consider additional COVID-19 vaccine doses as a key strategy to combat the evolving COVID-19 pandemic.

While the scientific evidence for boosters is encouraging, this strategy requires population acceptance and significant public health efforts. Even among those who have already received a two-dose series, there is a considerable portion of the population who are unwilling or undecided about receiving a third dose [8‐11]. However, adult perceptions on ongoing booster doses (i.e., annual COVID-19 vaccination) are largely unknown, and evidence on additional vaccine dose acceptance among Canadian adults, particularly among populations who may be at greater risk for COVID-19 infection and/or severe illness, is required. To ensure that COVID-19 vaccination programs are both acceptable and sustainable, we need an understanding of perceptions on strategies used to promote vaccine uptake over the long term, including vaccination mandates and restrictions, vaccination locations, and COVID-19 vaccine co-administration with other vaccines [12].

The aim of this study was to determine Canadian adults’ intention for receiving additional doses of COVID-19 vaccine (i.e., third or annual doses), and examine factors associated with acceptance. We further sought to understand influences on vaccination decision-making, and preferences around vaccine delivery location, and COVID-19 vaccine co-administration.

The survey was completed by 6010 adult respondents. Unweighted and weighted characteristics and vaccination intentions for the respondents are presented in Table 1. The majority of respondents (70.3%) reported that they planned to receive a third dose of the vaccine, while 15.2% and 14.5% reported they were undecided or refused to receive a third dose, respectively. Most respondents (64.7%) also reported acceptance of an annual COVID-19 vaccine dose, with the remaining respondents divided between undecided (17.5%) and refusal (17.8%).

We completed a national, cross-sectional survey to evaluate Canadians’ intentions to receive booster (third and annual) COVID-19 vaccine doses, at a time when recommendations on additional COVID-19 vaccine doses were evolving. We found that 70% of all respondents, and 78% of those who had completed a two-dose series, indicated they would accept a third dose of COVID-19 vaccine. The proportion of two dose recipients willing to receive a third dose of vaccine was somewhat lower than findings from surveys conducted in other countries during the same time period (79–95.5%) [8‐10, 21‐24]. However, more than 15% of respondents in our study reported they remained undecided about receiving a third dose, including over 10% of those who had not yet received any COVID-19 vaccines. Therefore, even in a population with high primary series coverage (almost 90% in our study), there is potential to improve uptake of both primary and additional doses.

Acceptance of an annual dose (65%) was lower than third dose acceptance (70%), indicating that, if COVID-19 vaccines are required on an ongoing basis, uptake may decline over time. Factors associated with accepting an annual COVID-19 vaccine were similar to third dose intentions; however, those of male gender, lower income, and visible minority identity appeared less likely to accept annual vaccination. Given that almost 20% of respondents remain undecided about annual COVID-19 vaccination, and the important influence of government and healthcare provider recommendations on vaccination decisions, acceptance is likely to be improved by clear guidelines around annual dose vaccinations, if or when they are required.

We found that many respondents with established risk factors for COVID-19 morbidity and mortality (e.g., higher age, pre-existing chronic conditions) were significantly more likely to report acceptance of additional COVID-19 vaccine doses. The relationship between increasing age and additional dose acceptance is similar to findings on third dose acceptance from other countries [9‐11, 22, 24]. Literature indicates mixed results on the impact of a pre-existing chronic condition on uptake of additional COVID-19 vaccines [8‐11, 23], though we defined chronic conditions more narrowly, as those at highest risk for COVID-19 morbidity/mortality. People who live with disability may also be at increased risk for both infection and negative disease outcomes, though risk varies with both type and severity of impairment [25, 26]. However, self-reported disability was not associated with higher odds of additional dose acceptance in our study; instead, these respondents were more likely to be undecided about additional dose acceptance. For some respondents, this could be related to concerns around vaccine service accessibility; approximately 8% of survey respondents indicated that improved vaccine service accessibility for all abilities would be important for making vaccination easier. To ensure those who plan to receive additional vaccine doses are able to act on their intentions, and facilitate uptake in those who are undecided, vaccine services must consider the needs of all abilities [27], and involve those who live with disabilities in service planning [28]. Improved understanding of potential barriers to vaccine uptake in this population is also required [29].

Our results indicated both concerning and encouraging relationships between sociodemographic factors and additional vaccine dose acceptance. Concerningly, lower socioeconomic status (i.e., lower household income and educational attainment) and visible minority status were related to less positive intentions toward receiving additional COVID-19 vaccines, though results were not always statistically significant. These findings are consistent with third dose vaccination intentions in the United Kingdom [10], though other research suggests socioeconomic status has little impact [11, 30]. Encouragingly, other populations thought to be at risk for undervaccination (e.g. newcomers, first language not English or French, Indigenous identity) in Canada [31], reported third dose vaccination intentions that were not significantly different from the general population or more positive. Results may reflect the success of specialized public health measures within these communities, minimizing previously existing health disparities [24]. However, some inequities remain, requiring further investigations.

It is also concerning that neither parental status nor employment as a healthcare worker was associated with more positive intentions around additional COVID-19 vaccine doses, as both populations have significant potential to influence the health and vaccination status of others. Parental intention for self-vaccination is a significant predictor for COVID-19 vaccination intent for their children [20]. Healthcare workers are consistently identified as important influences on vaccine uptake decisions, both here and in other literature [32], and those who are personally vaccinated are more likely to recommend vaccination to patients [33]. However, it is important to acknowledge that there is significant heterogeneity around vaccine acceptance within both parents [20] and healthcare workers [34], though stressing altruistic reasons for receiving additional doses (e.g. protecting children, protecting patients) may be effective for both [20, 35].

Unsurprisingly, both previous COVID-19 vaccination and seasonal influenza vaccination intention were significant predictors of favorable intentions towards additional doses. However, previous COVID-19 vaccine receipt did not uniformly predict acceptance of additional doses; more than 20% of those who had received two doses, and 60% of those who had received only one dose, did not accept additional doses. Our results indicate that COVID-19 disease history, and motivation for receiving initial doses, may explain some of that difference. In our study, those who had experienced COVID-19 disease were more likely to refuse additional vaccine doses. This relationship between previous infection and future dose refusal is not consistently found in the literature [8, 10, 11, 36], though timing of infection relative to vaccination may be important [10, 11]. Given that the evidence around vaccination after SARS-CoV-2 infection is still emerging [6], confusion over the need for, and timing of, vaccination post-infection is likely. As the number of people who have experienced SARS-CoV-2 infection continues to grow, clear messaging around the effectiveness of additional vaccine doses will be required. We also found that vaccination mandates or restrictions were the main motivation for previous COVID-19 vaccine receipt for significant portions of both the refusal (almost 50% of 419 respondents) and undecided (almost 20% of 837 respondents) groups, compared to less than 3% of the acceptance group (4179 respondents). Thus, while coercive measures may positively influence initial vaccine receipt, vaccination experience is not enough to overcome hesitancy toward additional vaccine doses. This supports observations that initial hesitancy about COVID-19 vaccination appears to persist, even after two-dose completion [10]. Other factors, including belief that sufficient protection is acquired through a two-dose series [8‐10], experiencing side effects from previous doses [8, 37], and concerns over receiving additional vaccine doses while other countries are struggling to secure first doses may also play a role [38].

While our results indicate that pharmacy-based delivery and drop-in appointments may increase COVID-19 vaccine uptake, offering co-administration of the COVID-19 vaccine with influenza or routine vaccines may not have the positive impact on uptake that is expected. In general, respondent attitudes regarding vaccine co-administration mirrored their intentions for additional COVID-19 vaccine doses; however, while almost 95% of the refusal group (N = 419) did not agree (disagree or neutral) with co-administration, only around three quarters of the acceptance group (N = 4179), and less than 17% of the undecided group (N = 837), agreed with co-administration. Thus, while more than 60% of all respondents agreed with COVID-19 vaccine co-administration, hesitancy towards co-administration is greater than hesitancy towards the COVID-19 vaccine alone. While there is some evidence to support this finding [12], one study found that a combination influenza/COVID-19 vaccine had higher acceptance than a COVID-19 vaccine alone [39]. More work is required to understand whether and how acceptance of co-administration differs from acceptance of combination vaccines, and whether these options differentially impact uptake across populations. Providing public choice around vaccine co-administration will be important to avoid negatively impacting future uptake.

Overall, intent to accept additional COVID-19 vaccine doses was high. We found that acceptance of annual COVID-19 vaccine doses was lower than acceptance for third doses, though clear guidelines and health care worker recommendations around the need for annual doses may increase uptake. Visible minority and minority language populations, and those with a disability, may be particularly receptive to interventions promoting and facilitating vaccine uptake. Efforts to promote vaccine uptake among parents of minor children and healthcare workers are needed to improve vaccine coverage overall. While approaches to facilitate access to vaccination services are important for continued uptake of COVID-19 vaccine, promoting vaccine co-administration may be less effective.