The evolution of vaccine hesitancy through the COVID-19 pandemic: A semi-structured interview study on booster and bivalent doses

ABSTRACT

We sought in-depth understanding on the evolution of factors influencing COVID-19 booster dose and bivalent vaccine hesitancy in a longitudinal semi-structured interview-based qualitative study. Serial interviews were conducted between July 25th and September 1^st, 2022 (Phase I: univalent booster dose availability), and between November 21^st, 2022 and January 11^th, 2023 (Phase II: bivalent vaccine availability). Adults (≥18 years) in Canada who had received an initial primary series and had not received a COVID-19 booster dose were eligible for Phase I, and subsequently invited to participate in Phase II. Twenty-two of twenty-three (96%) participants completed interviews for both phases (45 interviews). Nearly half of participants identified as a woman (n = 11), the median age was 37 years (interquartile range: 32–48), and most participants were employed full-time (n = 12); no participant reported needing to vaccinate (with a primary series) for their workplace. No participant reported having received a COVID-19 booster dose at the time of their interview in Phase II. Three themes relating to the development of hesitancy toward continued vaccination against COVID-19 were identified: 1) effectiveness (frequency concerns; infection despite vaccination); 2) necessity (less threatening, low urgency, alternate protective measures); and 3) information (need for data, contradiction and confusion, lack of trust, decreased motivation). The data from interviews with individuals who had not received a COVID-19 booster dose or bivalent vaccine despite having received a primary series of COVID-19 vaccines highlights actionable targets to address vaccine hesitancy and improve public health literacy.

KEYWORDS:

• Vaccine hesitancy
• COVID-19
• public
• interviews
• booster
• bivalent

Introduction

Mass COVID-19 vaccination campaigns commenced in December, 2020 and have since provided vaccines to more than 5.55 billion people worldwide or about 72.3% of the global population.^1,2 Individuals who received all recommended doses in the primary series of the COVID-19 vaccine (one or two doses, brand dependent) were considered fully vaccinated³; however, humoral immunity (i.e., an antibody-mediated response that occurs when foreign material – antigens – are detected in the body) toward COVID-19 declines around 6-months post-immunization.^4–6 Many have suggested that mass vaccination campaigns must continue in parallel, providing “booster” doses as a mediator for improving cell-mediated immunity (that does not depend on antibodies for adaptive immune function) and thus enhancing COVID-19 vaccine effectiveness.⁷

Booster doses for COVID-19 became readily available in December, 2021, around the same time that a new variant, called omicron (subvariant BA.1), was detected in southern Africa.^8,9 The omicron variant contained greater than 30 mutations in the spike protein,¹⁰ 15 of which were in the receptor-binding domain that was the primary target of neutralizing antibodies.¹¹ Serum samples obtained from individuals who were vaccinated against or previously infected with SARS-CoV-2 exhibited significantly lower neutralizing activity against BA.1 compared to the ancestral and other strains^12,13; many commercially available monoclonal-antibody preparations were rendered ineffective against this variant.¹⁴ Bivalent vaccines were created and distributed rapidly to counter the threat posed by omicron.^15,16

The World Health Organization (WHO) defines vaccine hesitancy as the “delay in acceptance or refusal of vaccines despite availability of vaccine services.” Core elements of vaccine hesitancy are mediated by individuals’ vaccine-related knowledge and health literacy levels.^3,17 Distinctly, vaccine hesitancy is not defined as the inverse of vaccine acceptance^18,19; individuals may receive a required dose eventually but postpone or delay the recommended schedule or, with regard to booster doses or bivalent vaccinations, may accept some – but not all – recommended doses or vaccinations.^20,21

Limbu and colleagues conducted a systematic review in 2023 to identify factors associated with COVID-19 booster dose hesitancy, some of which included perceptions of severity, efficacy, and susceptibility, as well as prior history of COVID-19 infection and COVID-19 vaccination status.²² Data from the United States National Immunization Survey (Adult COVID Module) in 2022 determined that just over half of the adult population had received both a primary series and more than one booster dose, highlighting prevalent disparities in racial and ethnic minorities, as well as adults living in poverty, with lower education, or without health insurance.²³ Our group²⁴ among others^25–27 have also identified low vaccination rates among healthcare providers for the COVID-19 primary series as well as for booster doses and the bivalent vaccine. Vaccine hesitancy among healthcare professionals is important, as it may influence community perceptions negatively and contribute to refusal or delayed uptake of COVID-19 vaccines.

In the current study, we aimed to examine the evolution of COVID-19 vaccine booster dose and bivalent vaccine hesitancy using a longitudinal qualitative research design. We conducted semi-structured interviews at two time points: when booster doses but not bivalent vaccines were available, and when both booster doses and bivalent vaccines were available. The study fills a critical gap in our understanding of the factors influencing COVID-19 booster dose and bivalent vaccine hesitancy and may inform possible targets for future interventions to reduce it.²¹

Methods

Study design

A longitudinal qualitative research design²⁸ was deployed and conducted in accordance with the Consolidated Criteria for Reporting Qualitative Research²⁹ (Supplemental Table 1) to examine the evolution of vaccine hesitancy across two time points of the COVID-19 pandemic. The 3C Theoretical Framework³⁰ was the underpinning framework for this study. Thematic results are presented and evaluated according to established guidelines.^31,32 This study was approved by the University of Calgary Conjoint Health Research Ethics Board (ID: 21–1241) and the Dalhousie University Health Science Research Ethics Board (ID: 2021–5782).

Table 1. Semi-structured interview participant characteristics.

Characteristic	N (%)
Province in Canada
Alberta	5 (22)
Manitoba	2 (9)
Ontario	8 (35)
Québec	3 (13)
New Brunswick	2 (9)
Nova Scotia	3 (13)
Age category, years
Median, IQR	37 (32, 48)
18–29	3 (13)
30–44	12 (52)
45–64	7 (30)
65+	1 (4)
Gender
Women	11 (48)
Men	12 (52)
Ethnicity
White	12 (52)
Asian	4 (17)
Black	3 (13)
Middle Eastern	1 (4)
Biracial	3 (13)
Education
Highschool or less	3 (13)
Some or completed post-secondary/college	18 (78)
Trade school	2 (9)
Employment Status
Unemployed	3 (13)
Part-time	2 (9)
Full-time	12 (52)
Other^Citation1	6 (26)

^aIncluding retired, student, and disabled.

Abbreviations: IQR, Interquartile Range; N, Number.

Setting

This was a qualitative follow-up study to an online national cross-sectional survey of Canadian adults that explored vaccine hesitancy during the COVID-19 pandemic.³³ Respondents to the primary study consented to be contacted for future COVID-19-related research.

Recruitment

We purposively sampled participants to ensure diversity in geographical location (British Columbia, Alberta, Saskatchewan/Manitoba, Ontario, Quebec, and Atlantic provinces), gender (man, woman, other), age (18–34, 35–55, >55 years), and ethnicity (White, Black/Indigenous/Persons of Colour). Participants were eligible for Phase I if they were English or French speaking adults (≥18 years) living in Canada who had received an initial primary series of COVID vaccines, but had not received a COVID-19 booster dose. Individuals who participated in a Phase I interview were subsequently invited to participate in an interview for Phase II; no new participants were recruited. Participants in both Phases provided informed, oral consent prior to participating in their interview. All individuals who agreed to participant were compensated with a $25 gift card for their time, after each interview.

Semi-structured interview guides

A semi-structured interview guide for Phase I was developed iteratively via consecutive working groups comprised of experts in vaccinology (DMH, SAH), public health policy (HTS), citizen engagement (SJM), and qualitative research (JPL). The 3C Theoretical Framework³⁰ (i.e., Confidence, Complacency, and Convenience) was the underpinning framework for development of the Phase I interview guide. The Phase I interview guide focused on: 1) perceived effectiveness of COVID-19 vaccines (Confidence); 2) reasons for hesitancy toward a COVID-19 booster dose (Complacency); and 3) perceived accessibility and understanding of vaccine information and vaccines themselves (Convenience). The Phase I guide was pilot tested with two eligible individuals from our related cross-sectional survey study³³; their data was included in the final analysis and were compensated $25 for their time. Minor refinement after pilot testing was to improve language and conversational flow. A semi-structured interview guide for Phase II was subsequently developed through the same working group process and also underpinned by the 3C Theoretical Framework.³⁰ The Phase II interview guide focused on whether and how participant perceptions (e.g., fears, concerns), intentions (e.g., motivations, plans), and behaviors (e.g., avoidance, acceptance) toward COVID-19 vaccines (including the newly available bivalent vaccine) had evolved since their Phase I interview. The interview guide for Phase I and the interview guide for Phase II are both available in Appendix 1.

Data collection

We conducted serial interviews between July 25^th and September 1^st, 2022 (Phase I: booster dose availability), and between November 21^st, 2022 and January 11^th, 2023 (Phase II: bivalent vaccination availability). Three researchers (EF, AD, MC) trained in qualitative research methods conducted Phase I and II interviews. All interviews were audio recorded via Zoom (https://zoom.ca) and subsequently transcribed verbatim by Rev.com (www.rev.com/). At the end of each of their interviews, participants were emailed a link to an online survey intended to collect relevant demographic information (e.g., age, gender, geographical location). The same three researchers (EF, AD, MC) reviewed, cleaned, and de-identified transcripts prior to analysis. As a form of member checking to maximize validity, participants were offered the opportunity to review and revise their interview transcripts; seven participants in Phase I and five participants in Phase II reviewed their transcripts, with all participants suggesting no changes.

Data analysis

We conducted inductive (for Phase I) and deductive (for Phase II) thematic analysis³⁴ using NVivo 12 software (QSR International, Melbourne Australia). First, for Phase I, two researchers (EF, MC) read all interview transcripts to familiarize themselves with the data. They then independently coded two Phase I transcripts in duplicate using open coding.³⁴ Initial codes were compared and revised, after which an additional three transcripts were coded; codes from these first five transcripts were used to develop the initial codebook. The same researchers (EF, MC) then analyzed 10 new Phase I transcripts using both open and axial coding³⁵; meetings were held (among EF, MC, SJM, and JPL) after coding of every two transcripts for the duration of analysis to address new codes, consolidate ideas, and rectify disagreements by consensus. All Phase I transcripts were then coded in duplicate by the same researchers (EF, MC) using the finalized codebook.

Phase II transcripts were analyzed deductively using the codebook developed in Phase I; data that did not fit within the Phase I codebook was marked for further discussion (among EF, MC, SJM, and JPL) and additional theme development.³⁶ The careful use of memos (by EF and MC) during Phase II analysis provided a visible ‘audit trail’ as the analysis of Phase II transcripts moved from ‘raw’ data, through interpretation, to the production of findings.

After Phase I and Phase II data were analyzed independently, a second analysis was conducted to focus on differences and similarities between time points. Themes and sub-themes for both Phases were then consolidated into a final set of themes and sub-themes that included both Phases. The final set of themes and sub-themes were then mapped to the 3C Theoretical Framework³⁰ by the broader research team (SJM, JPL, EF, MC) through meeting and discussion.

Results

Phase I included 23 participants and Phase II included 22 participants; one participant was lost to follow-up in Phase II for reasons unprovided. Nearly half of participants identified as a woman (11, 48%), were most frequently from Ontario (8, 35%), and more than half self-identified as White (12, 52%) (Table 1). The median age was 37 years (interquartile range: 32, 48), and most participants were employed full-time (12, 52%), though no participant reported needing to vaccinate (with a primary series) for their workplace. No participant reported having received a COVID-19 booster dose at the time of their Phase II interview.

Across both Phases, we identified three themes related to the development of hesitancy toward continued vaccination against COVID-19 that included: 1) effectiveness (frequency concerns; infection despite vaccination); 2) necessity (less threatening, low urgency, alternate protective measures); and 3) information (need for data, contradiction and confusion, lack of trust, decreased motivation). Themes and sub-themes as mapped to the 3C Theoretical Framework are provided in Table 2.

Table 2. Representative themes by the 3C theoretical framework.

3C Theoretical Framework	Theme and Sub-theme
Confidence
Trust in the safety and efficacy of vaccines, and the authorities and systems that deliver vaccines including their motivations.	Efficacy Frequency concerns Continuous infection
	Information Less threatening Contradiction and confusion
Complacency
Belief in risk of disease impact or infection, and the importance of vaccination for personal health and protection.	Necessity Low urgency Alternative measures
	Information Decreased motivation
Convenience
Availability, affordability, accessibility, and ability to understand information and services.	Information Need for proof

Effectiveness

Nearly all participants described an overall hesitancy toward the COVID-19 booster dose or bivalent vaccine that hinged on the concept of effectiveness, after witnessing colleagues, friends, and family become infected with SARS-CoV-2 despite having recently received a booster dose or bivalent vaccine.

Frequency concerns

Several participants questioned the effectiveness of the COVID-19 vaccine primary series when interviewed in Phase I and Phase II, as well as the effectiveness of subsequent booster doses and the bivalent vaccine. A primary consideration in Phase I was the frequency with which new vaccines and more doses were made available and recommended. Some participants described feeling uncomfortable with the idea of future injections:

“I do believe it would be possible to be vaccinated too many times. I feel like injecting more drugs, I guess, into your body, it’s going to have negative side effects at some point if it’s just continual.” (P12) Alberta, Woman, Phase I

“So, my question would be, why should we get it again, put even more stuff in our body if it hasn’t been really proved yet, or hasn’t been studied enough just yet?” (P1) Nova Scotia, Man, Phase I

When interviewed in Phase II, most participants compared their previous acceptance of one or two dose vaccines (e.g., Shingles) to their current hesitancy toward the COVID-19 booster dose or bivalent vaccine. One participant regarded the polio vaccine:

“Long-term studies and many of them such as polio vaccine, you take, it’s one or two shot maximum, you’ll let your body develop the antibodies and you’re done with this.” (P4) Quebec, Man, Phase II

While another participant described the chickenpox vaccine:

“I think the first two vaccines are good enough. Like the chickenpox, you only got a couple. I don’t think you really need to keep getting boosters every so often just because somebody says so.” (P13) Ontario, Woman, Phase II

Infection despite vaccination

Several participants, primarily in Phase II, reported becoming infected with SARS-CoV-2 even after receiving a primary series and/or knowing others who reported a comparable experience. For most of these participants, such experiences negatively impacted their belief in the effectiveness of COVID-19 vaccines. Two participants reported that infection was common within their inner circle:

“By no means do I know anything about medical research or vaccines … but I know so many people and myself, have got the COVID, even after getting two doses and even people who have got the booster, they’ve got it.” (P2) Manitoba, Man, Phase II

“I mean, I had the infection, and we were sick for a week. We did everything that I was asked of us for the first two shots, and I still got it. All my friends got it.” (P1) Nova Scotia, Man, Phase II

More participants commented in Phase II, compared to Phase I, that they had resigned to becoming ill with COVID-19 in the future, rather than receiving a booster dose or bivalent vaccine. These participants were not convinced that the booster dose or bivalent vaccine would further enhance their immunity:

“If it doesn’t reduce transmission, I don’t really see the point in taking this risk if it’s not going to actually help anything other than how well I deal with symptoms.” (P21) Ontario, Man, Phase II

“I’m really not confident about the booster dose because I feel that the first vaccinations and second vaccination should do what it’s meant to do to avoid people from catching COVID. That means if they weren’t sure about the first one, they created second one and why is they unsure? Why do we still have to have a third dose? Why do they have to bring booster dose to increase the rate at which people don’t get COVID?” (P5) Manitoba, Woman, Phase II

Necessity

All participants questioned the overall necessity of the booster dose and/or bivalent vaccine to prevent serious illness or injury after receiving their COVID-19 vaccine primary series, within one or both of their interviews.

Less threatening

In both Phases, SARS-CoV-2 was considered to be less and less of a threat to participants’ health and safety as the pandemic continued. Some participants compared COVID-19 to sessional influenza:

“I feel that the fact that there is diminishing severity just gives my chances even better of just handling it like another flu season or another cold. That’s where I’m at.” (P6) Alberta, Woman, Phase I

While others took comfort in their current vaccination status:

“And I had chickenpox when I was a kid, and because of the vaccines, it really wasn’t that bad. If I get COVID, I get COVID. I don’t think it’ll be as bad as if I wasn’t at all vaccinated.” (P3) Ontario, Woman, Phase II

In both Phases, participants commented that the Omicron variant appeared less virulent:

“My own personal health, I don’t think it poses that much of a risk. Well, it depends on which strain because the original SARS-CoV-2 virus, I have asthma, so I feel like that would put me at a huge disadvantage, and it was much more deadly. The current, I think, main strains are different variations of Omicron. It doesn’t seem as bad.” (P21) Ontario, Man, Phase I

“For the boosters, it was just like, you know what? The Omicron variant or whatever it might be, it wasn’t appearing very strong. I never did get sick, so I thought, why would I bother adding more?” (P9) Alberta, Man, Phase I

“So personally, I don’t think there’s much of a risk, and I know that the variants of COVID around now aren’t as deadly as they were in the first year of the pandemic.” (P14) Ontario, Man, Phase II

One participant noted in Phase I that the perceived reduced threat of COVID-19 was attributed, at least in part, to adequate uptake of the primary series:

“We know some people die or this is sad, but when you see as numbers, we can see, oh, that’s not so bad as they should be. But I think also the first and the second doses of the vaccines has contributed to this situation, to have this good situation now.” (P7) New Brunswick, Man, Phase I

Pandemic fatigue and the desire to move forward from the COVID-19 pandemic was most frequently heard from participants during their interviews in Phase II.

“Whereas I do feel we’ve always protected ourselves with vaccines wherever we can. I feel a little bit differently about COVID now, I think we need to carry on. I don’t think it’s the health threat that it once was.” (P12) Alberta, Woman, Phase II

“The time shows that, for me at least, and this is my personal point of view, this is a disease. We have to get used to that and keep driving.” (P7) New Brunswick, Man, Phase II

Low urgency

All participants described a low urgency to receive a booster dose or bivalent vaccine in one or both of their interviews. Some participants recognized their perception was attributed to provincial public health mandates, or lack thereof. One woman from Alberta described how regional vaccination mandates were a motivating factor for her receipt of the primary series:

“I guess one thing that would maybe make me more likely to get a booster is if they were mandated. A big reason why I got my first and second shot was so I could still have a life, I could still go out, I could still fly, I could still go to restaurants. If the vaccine passport type thing came back, I would be a little more inclined to get a booster.” (P8) Alberta, Woman, Phase I

Similarly, participants commented that booster dose and bivalent vaccine mandates was a large deciding factor in their decision of whether to become vaccinated:

“No, not yet. I’m just waiting to find out if it’s mandatory or not.” (P7) New Brunswick, Man, Phase I

“I think the main point for me is the lack of push that we’re seeing from government and news sources to get it has greatly impacted, the sky’s not falling like it once was back in March, 2020, so the edge has been taken off, and so I think that has led to kind of my passe type of belief style or the way I’m handling COVID.” (P6) Alberta, Woman, Phase II

“I think the main reason why I haven’t is that it’s not required.” (P21) Ontario, Man, Phase II

Several participants in Phase II identified that their low level of urgency was associated with the low level of urgency among others. Two women offered:

“I was waiting to see if a lot of people are taking the booster vaccine and they’re fine and they’re not getting contracted by the virus again. So that was the main hindrance of me waiting till this time to get the booster.” (P19) Quebec, Woman, Phase II

“That shows me that a lot of people aren’t getting it [the booster dose], and it makes me feel like if all these other people aren’t getting it, why do I have too as well, almost? That kind of mindset.” (P12) Alberta, Woman, Phase II

Alternate protective measures

Alternative measures of protecting oneself against SARS-CoV-2, beyond receiving continued vaccines, were noted by participants in both Phase I and Phase II. Participants in Phase I commented mostly that they remained at home for large portions of each day, thereby not necessitating further immunization for COVID-19.

“I’m mostly home about 90% of the time. So, I’m not really worried about it too much compared to other people that would be more active, people going on vacation, going in a restaurant, going sporting events. But me, it’s not a big concern.” (P7) New Brunswick, Man, Phase I

“I still work from home. I don’t have much interaction and I’m trying to wear a mask in public places. I don’t think it’s so necessary to get this vaccination done.” (P17) Ontario, Woman, Phase I

“I work from home. I don’t really do a whole lot outside the home other than day-to-day…not even day-to-day grocery shopping, stuff with the kids. We are out in the mountains hiking more than we are out doing things inside, indoors. That was one of the factors.” (P12) Alberta, Woman, Phase I

Participants in Phase II suggested primarily that their general good health and wellbeing was more effective to prevent against SARS-CoV2–1 than a booster dose or bivalent vaccine.

“I live a healthy lifestyle and I’ve had the original two shots and natural immunity, so I feel protected.” (P14) Ontario, Man, Phase II

“I mean, statistically I’m not at risk. I’m relatively young. I do not have comorbidities and I do not suffer from obesity … So I’m not the vulnerable part of the population regarding great complications. I am highly confident my body will fight that virus if I ever catch.” (P4) Quebec, Man, Phase II

Information

Participants across both Phases questioned the information they accessed on COVID-19 vaccines that included information on the primary series, booster doses, and bivalent vaccines.

Need for data

Participants highlighted their need for more data generally, and on vaccine efficacy more specifically. While some participants described a general lack of knowledge on COVID-19 vaccine development:

“I think that would have also assisted in people’s general comfortability with it [COVID-19 vaccines] and knowing that there’s actually a lot more science behind it than what they’re perceiving. For myself, I would have liked to have seen more of that [vaccine research] to get a better understanding as to how vaccines are done.” (P6) Alberta, Woman, Phase I

Others commented on inaccessibility of the information they were searching for related to COVID-19 vaccines:

“Had a hard time finding information about what exactly it [the vaccine] was. I couldn’t really get detailed information there … it was kind of vague. I’m not sure where to find the information. I found a little bit of information, but it wasn’t really enough to convince me.” (P7) New Brunswick, Man, Phase II

“I certainly haven’t been able to find as many studies to read through as I wanted. It’s tricky to find them, but I did find it easier now, looking for information on the bivalent vaccine than I did for the original vaccine when it came out. There do seem to be more published studies for people to be able to view themselves now.” (P10) Ontario, Woman, Phase II

Further, some participants directly stated their current need for more data prior to receiving any further immunization for COVID-19.

“I have got the two doses, but I haven’t got the booster dose just because these vaccines are not very effective on those variants. If they can be effective and if I get a solid proof of that, I’ll take the booster vaccine.” (P19) Quebec, Woman, Phase I

“I’d like more…testimonies from people who have the shot. What was their experience and how are they doing? How do they feel? It’s all great to get government information, but I need it from someone who’s on the ground, who’s going through the day today, just like me.” (P18) Quebec, Man, Phase II

Many participants voiced their overall desire for more easily accessible information explaining how vaccines work in general. One man from Ontario suggested increased health literacy more generally:

“But when it comes to what I would like to understand or like people to understand honestly is how vaccines and booster shots work in general. Because you do see, we eradicated some viruses with the vaccines, but then you do hear that they kind of come back, not as bad as when they used to, but they do come back. So it’s like why not talk about these subjects so people can understand them… you know what I mean?” (P15) Ontario, Man, Phase I

Contradiction and confusion

All participants, across both Phases, highlighted that the information they did access was often contradictory, which formed the root of considerable confusion regarding COVID-19 vaccines. Some participants described contradictory information between researchers and healthcare professionals:

“It got me more confused than ever, because some scientists are saying do it [receive the booster dose], some were saying don’t do it, but my doctor always suggested I do it, but in the end I just didn’t do it.” (P22) Manitoba, Man, Phase I

Whereas other participants pointed for government and public health officials as the root of profound confusion:

“Actually, the main point is the government and the people on media. They say many things and all of those things they are saying … we are not sure if the vaccine is really effective, because they say, “Oh, it’s okay. We found a new vaccine,” or later, people starting to be, to have contagious again. “And oh, now we have another version, another version, another shot,” and so those kind of misinformation from the government and from the agencies, they confuse us.” (P16) New Brunswick, Man, Phase II

Some participants in their Phase I interview commented specifically on their weak understanding of vaccine platforms.

“Moving on through the pandemic, I was starting to get dubious of the vaccination, especially because why were we doing an mRNA vaccination? It was never really clearly explained to me why we’re doing this format and not just the traditional format. So, I was just confused why we’re doing this and not offering a regular vaccine option. I don’t think it was ever explained to me still.” (P21) Ontario, Man, Phase I

“I don’t know enough about the subjects, even the mRNA science itself. I didn’t understand a lot of it.”(P9) Alberta, Man, Phase I

Despite these barriers, several participants described attempts to make their own decisions after self-driven research.

“I would use my own common sense or if I had a question. I would ask the pharmacists where I work just to see what they think of the subject. But I did notice that because we do have different premises, I did notice that everyone gives a different answer so that doesn’t help either.” (P11) Ontario, Woman, Phase I

“I’ll see what information pops up, then I’ll compare that to the information on the government websites and then I’ll kind of split it down the middle, try to pick out what makes sense, what doesn’t make sense, and then I’ll just take it from there.” (P4) Quebec, Man, Phase II

Lack of trust

Across both interview Phases, trust in the source of information accessed was generally regarded as low or lacking among participants. One man from Manitoba detailed how his family physician was seemingly uncertain when asked specific COVID-19-related questions:

“I don’t think she [family doctor] knew either, because she was stumped on some things I would ask her. She just wouldn’t know. I don’t think they were very well informed either … I didn’t have much faith in my doctor. I really did before COVID. She was very good. She’s been looking after my health for a long time now, and she’s okay again, but during COVID it was just … I don’t know. She just didn’t seem to be giving me the information I was reading online, but I know you should always take your doctor’s advice over what you read online anyway.” (P22) Manitoba, Man, Phase I

A woman from Ontario noted how the universal need for funding may bias delivery of the facts:

“When we have stakeholders, each of them has own opinion, and they can influence on it. Right? And we don’t have anything what can be totally independent. Probably some kind organizations like NGOs can be on this way until they get paid. Right? But each of them needs funding that’s why all time they have to accept somebody’s side.” (P17) Ontario, Woman, Phase II

Some participants described their critical review process for articles that they accessed to learn more.

“Any of that stuff, it’s like you’ve got to pick through it. There’s so much stuff that’s really hard to verify if it’s actual fact or not? That was the biggest problem. You’ve got to read tons and tons of stuff and sift through and see if stuff’s making sense or see it from more different places, or if they’re reputable, like research. Who did it? See what their background is. That’s what I found that we live in an age where there’s too much information, and you don’t know what to trust and what not to trust.” (P20) Alberta, Man, Phase I

Decreased motivation

As the pandemic continued, participants experienced decreased motivation to access information on COVID-19 and to learn about new concepts related to booster doses and bivalent vaccines. In Phase I, participants described how their motivation had waned since the start of the pandemic.

“I haven’t been paying as much attention. I was paying a lot more attention during that first year when the vaccines were first rolled out. And I haven’t really been keeping up with it as much with the booster phase.” (P2) Manitoba, Man, Phase I

“I’ll read one, two or three [articles], and then see what makes sense and what doesn’t. And if it’s too confusing, I just ignore the subject totally, because I’m like, “I’m not going to get involved in something that I don’t know.” (P13) Ontario, Woman, Phase I

For many participants, their decreasing motivation plummeted to a deliberate action to pay no attention and to not seek out information on further COVID-19 vaccines. As told by two participants:

“I do not read, and I do not pay attention much. I think we have to live and that it will go away.” (P16) New Brunswick, Man, Phase II

“I have family that tell me things once in a while, but I don’t listen to that because I just have no interest in the booster.” (P3) Ontario, Woman, Phase II

Discussion

We conducted a two-Phase longitudinal semi-structured interview study to explore the evolution of vaccine hesitancy throughout the latter years of the COVID-19 pandemic as it related to booster dose recommendations and bivalent vaccines. Across both Phases, reasons identified as significant barriers to vaccination could be conceptualized by the 3C Theoretical Framework.³⁰ Our findings indicated that vaccine hesitancy in the context of COVID-19 booster doses and bivalent vaccines to control spread of the SARS-CoV-2 virus was connected to low urgency and reliance on alternative measures of protection (that suggested heightened complacency), as well as experiencing reduced severity of illness when infected with SARS-CoV-2 (highlighting a greater confidence in ‘acquired’ immunity). Hesitancy toward booster doses and bivalent vaccines that participants in our sample experienced after receipt of the COVID-19 primary series largely hinged on the notion that despite vaccines being readily available, information on vaccine effectiveness and adverse effects, was not (demonstrating their need for convenience of information).

Consistent with recent studies showing persistent complacency in COVID-19 vaccination uptake and attitudes,^37–39 and recent evidence on low perceived risk and worry toward the disease,^40,41 we found that complacency was the most frequently reported reason for COVID-19 booster dose hesitancy. Complacency is influenced by general health beliefs and occurs when individuals have a lower perception of the need for a vaccination or a lower perceived risk from diseases.⁴² For some, perceptions regarding the strength of immunity from previous infections among those who recovered from COVID-19 may be a facilitator for complacency.⁴³ Misconceptions or misunderstanding of vaccine efficacy and safety as well as misinformation in social media may also lead to complacency and result in under acceptance of the COVID-19 booster dose.^44,45 Additionally, the belief that widespread vaccination of others is sufficient to prevent transmission may result in one’s COVID-19 infection risk to be low.⁴⁶ Among studies that have measured COVID-19 booster dose uptake, “self-needs” and prosocial values were most frequently reported.^47–49 In addressing booster dose complacency, public health officials and governmental authorities should honestly communicate both known and uncertain risks of repeated infection that could be provided in parallel to public campaigns encouraging timely receipt of vaccines using extrinsic motivators to schedule and receive booster doses.⁵⁰

Trust is a strong driver in reducing vaccine hesitancy⁵¹ that was emphasized among participants regarding COVID-19 bivalent vaccines. Individuals with higher trust in health authorities have more positive perceptions of COVID-19 vaccines generally.^52,53 A crisis of trust in the COVID-19 vaccine, as well as in vaccine manufacturers and health facilities arose because of vaccine safety-related events and the rapid dissemination of false information.⁵⁴ Various studies have reported that trust in health authorities build when individuals feel that health authorities possess knowledge and expertise, consider all relevant opinions, and that authorities are transparent, honest, and open.^39,55 Providing accurate information in a transparent manner and establishing public communication channels with health authorities on bivalent vaccine effectiveness and risk may assist in fostering trust and enhancing confidence in the COVID-19 bivalent vaccine.⁵⁶ Identifying and addressing the concerns of those who have previously been infected with COVID-19 despite prior vaccination would also be beneficial to build trust thereby promoting vaccination.⁵⁷

Our findings highlight actionable targets for public health authorities to address vaccine hesitancy and improve public health literacy more broadly. Some participants in our study drew unfavorable comparisons between COVID-19 vaccines with other serial vaccines such as those to immunize against chickenpox (i.e., only two doses for the latter are required).⁵⁸ Strategies in which COVID-19 and seasonal influenza vaccines are administered simultaneously or combined into a single preparation may increase vaccine uptake as many populations have already been accustomed to taking influenza vaccines annually.^59,60 We also identified a general perceived lack of need to receive COVID-19 vaccines overall. Effective approaches to address this knowledge gap may involve preemptively reducing vaccine hesitancy through instilling confidence in vaccine benefit with how and why additional doses and vaccines are different. This approach has been successful previously within the context of seasonal influenza by focusing on confidence (through debunking misconceptions and increasing awareness of an ethical and professional obligation to vaccinate) within hospital settings.^61,62 Betsch and colleagues have also used the 3C Theoretical Framework to identify that informational interventions such as educational campaigns are a suitable means to address low confidence in seasonal influenza vaccines.^63,64 Dai and colleagues conducted a randomized controlled trial to test the effect of behavioral interventions on the uptake of COVID-19 vaccines.⁶⁵ Their text-based reminders that made vaccination salient and easy, boosted appointment and vaccination rates by 6.07 (84%) and 3.57 (26%) percentage points. Finally, the COVID-19 pandemic underscored that the public no longer implicitly trusts public health officials for their position in society or authoritative role.^66,67 This complex relationship includes a fragility of beliefs and perceptions at an individual level, with a bidirectional relationship to societal perceptions.⁶⁸ Understanding different types of trust (e.g., social, institutional, individual) offers potential approaches to motivate undecided people to receive vaccines; and vaccine refusers to revisit their decisions.⁶⁹

There are several strengths to our study. The semi-structured interview guides were developed and informed by our nationally representative cross-sectional survey of adults in Canada³³ and in-depth narratives on the COVID-19 pandemic,^22,70,71 co-designed with experts in vaccinology, public health policy, citizen engagement, and qualitative research, underpinned by the 3C Theoretical Framework,³⁰ and pilot tested with public citizens who self-reported experiencing vaccine hesitancy toward the COVID-19 booster dose. We conducted interviews at length, which allowed participants space and time to offer important insights and share perspectives. Our longitudinal study design^72,73 with near-perfect participant retention permitted analysis of booster dose and bivalent vaccine hesitancy that incorporated both inductive and deductive thematic analysis.

There are also limitations to consider when interpreting the findings of our study. First, the number of participants included in this study was dependent on the interest of survey respondents in our primary study for being contacted to participate in additional research projects.³³ We conducted interviews at two separate time points thereby doubling the time required to participate that may have limited interest and recruitment, although our retention across phases was high.^74,75 Second, to be eligible for a Phase II interview required completion of a Phase I interview; it is possible that bivalent vaccine hesitancy may exist separately from booster dose hesitancy⁷⁶ and as such, important perspectives may have been missed.⁷⁷ Third, although the 3C Theoretical Framework incorporates various perspectives required to better understand vaccine hesitancy, multiple factors influence vaccine hesitancy.⁷⁸ Numerous models of behavior change such as the Health Belief Model⁷⁹ have been applied to determine the reasons behind individual behaviors; perceptions of susceptibility to infection, severity of the virus, types of barriers, and potential benefits are all involved in behavior change.⁸⁰ We suggest that utilizing complementary frameworks, theories, and models to understand individual behaviors and the perceptions that influence those behaviors can provide valuable insight on changeable behavior barriers and the potentially effective strategies to overcome them.^81,82 Finally, our sampling frame did not allow us to explore sociocultural factors, including linguistic, technical, and cognitive barriers, which might impact vaccine hesitancy.^83,84 The majority of participants in our sample were White, and findings may have been different among racialized participants given that these populations in Canada experienced more severe COVID-19-related outcomes.^85,86 Additional research that provides in-depth understanding on experiences and perspectives of individuals who typically face additional barriers in times of crisis is needed.

Conclusion

Vaccine hesitancy toward COVID-19 booster doses and bivalent vaccines remains a public health threat. Our findings from serial interviews with individuals who had not received an available COVID-19 booster dose or bivalent vaccine despite having received a primary series of COVID-19 vaccines suggest that timely and transparent communication regarding vaccine risks and effectiveness as well as known and uncertain risks of repeated COVID-19 infections using extrinsic motivational techniques are actionable strategies to improve vaccine uptake and public health literacy.

Author contributions

All authors (JPL, EF, SJM, MC, RBM, AD, HTS, EB, KMF, DMH, SBA, SEM, SES, TM, JNK, AS, SL, SK, BS, SAH) contributed to the conception and design of the study. Authors (JPL, EF, SJM, MC, RBM, DMHDMH, SL, SK, BS, SAH) developed the semi-structured interview guide. Authors (JPL, EF, SJM, MC) analyzed the data and prepared the original draft of the manuscript. All authors provided critical revisions and approval of the final manuscript.

Availability of data and material

The datasets generated and analyzed are not publicly available as we did not secure direct permission from the survey respondents to share the de-identified dataset with the general public. Requests for the data can be directed to the institutional research ethics boards overseeing the conduct of the study via the corresponding author, Dr Jeanna Parsons Leigh.

Consent to participate

Informed consent was obtained from all participants included in the study.

Ethics approval

The study was approved and performed in accordance with the ethical standards of the Research Ethics Boards of Dalhousie University (#2021–5782) and the University of Calgary (#21–1241).

Disclosure statement

SAH has served on national and provincial advisory boards including, Federal and Provincial COVID-19 advisory committees, the Nova Scotia Vaccine Expert Panel, the Canadian Immunity Task Force, and the Canadian Vaccine Surveillance Reference Group. SAH has also served on industry ad hoc advisory boards for COVID-19 including Pfizer, Medicago, AstraZeneca, and NovaVax. Lastly, SAH has participated in COVID-19 clinical trials with Entos, VIDO, VBI, Medicago, Moderna, and CanSino.

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website at https://doi.org/10.1080/21645515.2024.2316417

Additional information

Funding

This work was supported by the Canadian Institutes of Health Research, Operating Grant: Emerging COVID-19 Research Gaps & Priorities – Confidence in science [#177722]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.