Hesitancy towards the COVID-19 booster vaccination: a thematic analysis from a focus group study in Spain

Abstract

Background

The aim of this study was to evaluate beliefs about and attitudes towards COVID-19 booster vaccination among subjects who had received the complete vaccination schedule but had not received the booster.

Methods

We conducted a qualitative study using online focus groups made up of participants from all parts of Spain who had received the primary vaccination schedule but had subsequently refused any of the booster doses. Individuals were recruited by snowball sampling.

Results

The study used 5 focus groups having a total of 30 participants. The thematic analysis identified 10 themes and 32 subthemes. Gynaecological problems and long-term adverse effects were associated with booster hesitancy. Participants perceived the vaccine as less necessary, as they considered it incapable of halting transmission and believed that the risk was much lower than at the onset of the pandemic. Rapid development of the COVID vaccine as compared to that of traditional vaccines, coupled with continuous changes in information, generated distrust and contributed to booster vaccine hesitancy.

Conclusions

Vaccine hesitancy can appear at any time and with any vaccine despite its evident public health benefits, as is the case of COVID-19 booster doses. Policy-makers should therefore focus on generating trust and responsibility when it comes to booster vaccinations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-026-26674-0.

Introduction

Vaccine hesitancy is defined as the delay in acceptance or refusal of vaccination despite availability of vaccination services [1]. It arises when there is indecision about vaccination, whether because of doubts regarding the vaccine’s safety or efficacy, or because of distrust in institutions, among others [2, 3]. This moment of indecision marks an intermediate stage, from which the individual may then advance towards being for or against vaccination [4]. Vaccine hesitancy has existed since early vaccines (influenza, HPV, polio, measles) and has intensified in recent years [5, 6]. The situation is so serious that in 2019, vaccine hesitancy was recognised as being one of the main threats to public health by the World Health Organisation (WHO) [7, 8].

Indecision about vaccination has grown noticeably in Spain, coinciding with the voluntary administration of booster doses against COVID-19 infection. Boosters began mainly at the end of 2021 for very high-risk groups and older people, expanding progressively to the general population in 2022 (85% coverage in the complete schedule versus 56% in the third dose [9, 10]). These ARNm designed boosters (Pfizer-BioNTech and Moderna) were administered 4 to 6 months after having received the complete schedule [11]. Despite the extensive coverage achieved by the complete schedule, the population’s willingness to receive the booster dose was very low. The extension of virus protection measures and the fall in the perceived risk, with COVID-19 being considered less serious than at its onset [12], generated a generalised feeling of oppression and a longing for freedom and social intercourse. This was linked to a lower degree of adherence to protection measures, including vaccination [13]. As a consequence, there was an increase in pandemic fatigue and complacency about the virus, both of which can prove as harmful as the disease itself, according to the WHO [14].

There are very few studies on booster vaccine hesitancy, and although they apply thematic analysis, they are carried out in very different contexts and do not focus exclusively on individuals unvaccinated with the booster dose [13–15]. In such a situation, qualitative methods can be of great help, since they enable in-depth examination of beliefs and attitudes that can lead to the emergence of barriers to certain types of behaviour. Achieving this with any other methodology would be far more difficult [16]. The aim of this study was thus to evaluate beliefs about and attitudes towards COVID-19 booster vaccination among subjects who had received the complete vaccination schedule but had not received the booster.

Methods

Study setting and design

We carried out a qualitative study using the focus group (FG) technique. The study was conducted with participants from Spain, which has a total of 47 million inhabitants [17]. In Spain, COVID-19 vaccination was initially structured as a complete schedule (administration of the first two doses) plus a subsequent booster (third and fourth doses [18]). Although a high vaccination percentage was initially achieved with the complete schedule, this fell significantly during vaccination with the booster [19].

Online FGs were formed because they involve a lower financial and logistical cost than do in- person FGs and allow for the same degree of interaction among the participants. This method allowed geographically diverse participation and ensured safety and accessibility post-pandemic. This study was conducted in accordance with the Consolidated criteria for Reporting Qualitative Research (COREQ) [20].

Selection, sample and procedure

Participants were selected using snowball sampling, as this methodology aims to capture a range of perspectives on the topic under study rather than to be representative of the population, and because of the difficulty in obtaining participants [21]. Snowball sampling initially encompassed individuals known to the researcher, who in turn served as key informants facilitating other individuals potentially eligible to participate in the study [22]. For study purposes, the inclusion criteria required that participants be aged 18 years or over, and of their own volition, had not been vaccinated with any of the booster doses administered in Spain (third or fourth dose). The exclusion criteria were having not received a booster dose due to medical indication or having failed to receive any of the doses of the full primary vaccination schedule, as well as having technological or communication difficulties that prevented participation in the focus groups. Participants were initially contacted telephonically (via WhatsApp or telephone call) and asked to participate, after the study objectives had been explained to them. If they agreed to participate, they were sent a link via WhatsApp or e-mail to assess their availability. Groups were then formed with those individuals who coincided in terms of their availability to participate in an FG. One day before the scheduled FG session, participants were sent a reminder and a link so as to be able to participate. Before the meeting began, they were likewise reminded of the study goals and method, and consent was obtained from each. The final number of FGs was based on the principles of data saturation, i.e., group sessions were held until such a time as no new topic emerged. The online sessions were held in groups of 5 to 7 persons, from January to March 2023.

In order to organise the topics to be addressed by the groups, we developed a semi-structured interview guide (see Supplementary Material 1) based on a review of the existing literature [23] and on previous FGs formed by the research team in the field of vaccine refusal. In addition, we were assisted by a group of epidemiology and pharmacology experts, as well as a psychologist (AF, MZC, ALD).

The FGs were conducted in Spanish and guided by an interviewer (APC) via a video link, using the Microsoft Teams platform. As a means of ensuring at the end of each session that all the topics of interest had been covered, a checklist was drawn up. The sessions lasted approximately 60 min. They were all tape-recorded after the participants’ prior consent had been obtained. Once the recordings had been analysed, they were deleted. APC made the literal transcriptions and then listened to each recording again 2 days later to ensure that it had been accurately transcribed. All participants were coded with an alpha-numeric code as follows: Alex, Quinn, etc.

Ethical considerations

The Galician Clinical Research Ethics Committee reviewed the study on December 16, 2021 (ID 2021/510) and ruled that, given its nature, no approval was required. Even so, prior to each session all the participants gave their oral consent to participate in the study. Participants could refuse to have their images shown on camera. Transcriptions were anonymised by generating a code for each participant. Only the research team had online access to data gathered in the study.

Data analysis

The results were analysed using inductive thematic analysis [24]. Firstly, APC read the transcriptions a number of times to familiarise herself with the data. She generated the initial codes, reviewing the noteworthy characteristics of the data from which the subtopics and ultimately the topics were then drawn. The initial codes, subtopics and topics so created were reviewed by AF and MZC. Discrepancies were resolved by consensus. Lastly, APC, AF and MZC agreed on the quotes that best represented the essence of the topics to be included in the Results section of this paper. No software was used for data-analysis purposes.

Results

Finally, 30 persons participated in 5 online FGs (Table 1). The online sessions were held in groups of 5 to 7 persons, from January to March 2023.

Table 1.

Focus group characteristics

Characteristics	Group 1 (n = 7)	Group 2 (n = 6)	Group 3 (n = 6)	Group 4 (n = 5)	Group 5 (n = 6)
Age
Mean (SD)	38.9(12.9)	36.3(11.6)	33(12.0)	28.4(6.8)	32.3(7.6)
Sex, No. (%)
Female	4 (57.1)	3(50.0)	4(66.7)	2(40.0)	2(33.3)
Male	3(42.9)	3(50.0)	2(33.3)	3(60.0)	4(66.7)
Area of residence, No. (%)
Urban	5(71.4)	4(66.7)	3(50.0)	2(40.0)	4(66.7)
Rural	2(28.6)	2(33.3)	3(50.0)	3(60.0)	2(33.3)

The socio-demographic characteristics of the 30 participants who participated in the respective FG sessions are shown in Table 1. After transcription and analysis, nine topics and 29 subtopics were identified that addressed beliefs about and attitudes to booster vaccine hesitancy. The main topics and subtopics are detailed in a thematic diagram (see Supplementary Material 2). The topics and subtopics identified, along with the discussion groups in which they emerged, are listed in Table 2. Table 3 carries quotes of remarks made by the participants in respect of the topics. The complete set of results, with all participant quotes integrated, is provided in Supplementary Material 3.

Table 2.

Thematic analysis: topics, subtopics and focus groups in which they emerged

TOPIC	SUBTOPIC	FG1	FG2	FG3	FG4	FG5	QUOTES
1. ADVERSE EFFECTS	1.1. Menstrual cycle	✓	✓	✓	✓	✓	28
	1.2. Mild	✓	✓	✓	✓	✓	18
	1.3. Influenza symptomatology	✓	✓	✓		✓	17
	1.4. Paresthesia	✓	✓	✓	✓	✓	15
	1.5. Cardiovascular	✓	✓	✓		✓	15
	1.6. Blood clots	✓		✓	✓	✓	13
	1.7. Benefit/risk ratio	✓		✓	✓	✓	13
	1.8. Causality	✓	✓	✓			13
2. VACCINE PROTECTION	2.1. Immunisation	✓	✓		✓	✓	20
	2.2. Transmissibility	✓	✓	✓	✓	✓	19
	2.3. Not strain-specific	✓	✓		✓	✓	17
	2.4. Natural protection	✓	✓	✓	✓	✓	17
3. NEED FOR VACCINES	3.1. Currently lower risk than at onset	✓	✓	✓	✓	✓	214
	3.2. Risk population	✓	✓	✓	✓	✓	9
4. VACCINATION IN CHILDREN	4.1. Long-term effects	✓	✓		✓	✓	17
	4.2. Not enough tests	✓	✓	✓	✓		16
	4.3. Milder COVID	✓		✓	✓	✓	13
5. PHARMACEUTICAL INDUSTRY	5.1. Efficacy and safety not sufficiently proven	✓	✓	✓	✓	✓	29
	5.2. Financial profit	✓	✓		✓	✓	17
	5.3. Quick solution	✓		✓	✓	✓	16
6. DIFFERENCES BETWEEN COVID VACCINES	6.1. All the same	✓	✓	✓	✓	✓	10
	6.2. Different		✓		✓	✓	6
7. INFORMATION	7.1. Disinformation	✓	✓	✓	✓	✓	20
	7.2. Changing information	✓	✓	✓	✓	✓	16
	7.3. Data-sources		✓	✓	✓	✓	15
8.POLICY-MAKERS	8.1. Late/poor action	✓			✓	✓	16
	8.2. Understanding	✓	✓	✓			15
9. SOCIAL PRESSURE	9.1. Leisure	✓		✓	✓		7
	9.2. Work		✓	✓	✓		3
10. OTHER NON-COVID VACCINES	10.1. Pro-vaccine	✓	✓	✓	✓	✓	19
	10.2. Vaccines received	✓	✓	✓	✓	✓	19
	10.3. Influenza vaccination	✓		✓	✓	✓	16

Table 3.

Thematic analysis: topics, subtopics and example quotes

TOPIC	SUBTOPIC	QUOTES
1. ADVERSE EFFECTS	1.1. Menstrual cycle	1.1.1. “People around me had told me about not getting their period any more, I myself began to get it very irregularly, and people started getting it in a different way.”(Reeve). 1.1.2. “I have gynaecological problems because of the vaccines.” (Alex).
	1.2. Mild	1.2.1. “Fever, headache, malaise, muscle pain…” (Grey). 1.2.2. “Pain in the axillary lymph nodes.” (Sam).
	1.3. Influenza symptomatology	1.3.1. “After the second dose I missed work because I felt like I was getting the flu.” (Kai). 1.3.2. “I got vaccinated and had the flu.” (Fin).
	1.4. Paresthesia	1.4.1 “I had a numbness in my jaw and left arm, and I told myself this is like a heart attack. So that was when I got a fright, and I thought I had to go to the emergency department. But after a short time, it went away.” (Alex). 1.4.2. “The case that most shocked me was temporary, my friend found she was paralysed in the face and in the arm. She got a real fright.” (Ash).
	1.5. Cardiovascular	1.5.1.“One person had a heart attack the week after vaccination.” (Lane). 1.5.2. “Because of all the vaccines and all that, the level of heart attacks in young and even middle-aged people went up a lot, at least among the people I know.” (Wynn).
	1.6. Blood clots	1.6.1. “Or this friend of mine, who after getting vaccinated had thrombosis.” (Drew). 1.6.2. “The worst thing was the blood clot thing.” (Sam).
	1.7. Benefit/risk ratio	1.7.1. “Do I die from COVID or do I let the vaccine kill me? Well, I said, let the vaccine kill me.” (Fin). 1.7.2. “What’s worse, the effects of vaccination or the effects of COVID? Because COVID itself also has effects.” (Sam).
	1.8. Causality	1.8.1. “That person might have had a heart attack just the same, even if he hadn’t got vaccinated.” (Wren) 1.8.2. “You don’t know whether all these effects are side-effects of the vaccination. And anyway you’re never going to know if it’s from the vaccine or not.” (Shea).
2. VACCINE PROTECTION	2.1. Immunisation	2.1.1. “If I had such a bad time of it getting vaccinated, imagine what could happen if I wasn’t vaccinated?” (Leem). 2.1.2. “With the first vaccination, we were absolutely clear about the fact that we were not going to be totally immunised. What it was going to do was to minimise the disease or prevent admissions to intensive care.” (Fox).
	2.2. Transmissibility	2.2.1. “I believe that they do protect you […] But if it was, say, something that made transmission difficult, I’d like it better.” (Ash). 2.2.2. “I didn’t have the jab for a number of reasons, for instance, the fact that it didn’t stop transmission.” (Wren).
	2.3. Not strain-specific	2.3.1. “There’s no sense in continuing to have the same jab when there are new COVID variants, and they know that the current vaccine isn’t effective against the new variants.” (Kai). 2.3.2. “As I understand it, they always give us the same vaccine. But no, I think that there should be one every year or that the guideline should change according to the strains that are circulating at any particular time. Otherwise, there’s no sense in always having the same jab.” (Alex).
	2.4. Natural protection	2.4.1. “I feel that by having the disease, that’s when you tackle the virus most completely.” (Rowan).
3. NEED FOR VACCINES	3.1. Currently lower risk than at onset	3.1.1. “I didn’t have the fourth jab, but whew, I’ll have to see when the time comes and how the symptoms develop.” (Mars). 3.1.2. “In the context in which we find ourselves now, I wouldn’t get the jab, but well, if a new super aggressive variant does indeed appear, and hospitalisations begin to go up, and you see that it’s highly virulent, well obviously. What do we prefer, being in intensive care or being a week with side-effects? That’s the question.” (Remy).
	3.2. Risk population	3.2.1. “For the population at risk, sure, but does it really make sense for the general, healthy, young population?” (Kai). 3.2.2.“In a young population it isn’t necessary… just like we don’t get a flu’ jab: it’s a virus. In people at risk, maybe yes.” (Shea).
4. VACCINATION IN CHILDREN	4.1. Long-term effects	4.1.1. “We never know what’s going to happen, or what side-effects a vaccine’s going to have in 5 to 10 years’ time on a child who’s in the most important stage of development.” (Lee). 4.1.2. “Now, I don’t rightly know, maybe I wouldn’t have had him vaccinated. In the long term, you don’t know the consequences, and we aren’t going to know whether it was better having had the jab or not. But there’s always going to be a doubt. At least in my case.” (Grey).
	4.2. Not enough tests	4.2.1. “They didn’t do as many tests on them as on adults.” (Quinn).
	4.3. Milder COVID	4.3.1. “The kid recovered in 2 days and I recovered in a month.” (Alex). 4.3.2. “All the cases that I saw in children who’d had COVID between the ages of 5 and 11 were pretty mild, so the truth is that I’d do as much as possible to avoid injecting them with anything external at that age.” (Wynn).
5. PHARMACEUTICAL INDUSTRY	5.1. Efficacy and safety not sufficiently proven	5.1.1. “It came out very quickly. Perhaps it should have been tested more, with more years of development. And yes it’s obvious that there are going to be gaps, and there are going to be procedures that have to be skipped.” (Sam). 5.1.2. “The trial phase wasn’t long enough to claim that the vaccine is safe. Not only do anti-vaxxers come from the general population, but there are also people who would have the vaccines, but because they haven’t been tested, they’re not inclined to trust them.“ (Wren).
	5.2. Financial profit	5.2.1. “Ultimately, the pharmaceutical industry is a corporate entity, it has to make money, make a profit, and with this thing they certainly made a packet, but then again that’s what they do.” (Shea). 5.2.2. “If these people hadn’t been paid what they’ve been paid, it’s likely we’d still be in the situation we were in two years ago.” (Cove).
	5.3. Quick solution	5.3.1. “They say that vaccines have a 5 or 6-year trial period […] but when you have a problem of that sort, what are you going to do? Wait until half the population dies?” (Ash). 5.3.2. “They made a massive effort, because the thing is that we couldn’t allow the virus to take over completely and let so many people die.” (Sam).
6. DIFFERENCES BETWEEN VACCINES	6.1. All the same	6.1.1. “The side-effects, at least they were practically the same in almost all cases. And they also protected us, as far as we can see.” (Fox). 6.1.2. “I took Pfizer and I also took the other one, and I had the same side-effects.” (Wynn).
	6.2. Different	6.2.1. “People have a pretty negative opinion about AstraZeneca, and at one time the Pfizer vaccine experienced a real boom.” (Reeve). 6.2.2 “People who got vaccinated with AstraZeneca had a range of symptoms for the next few days, whether stomach or flu’-type symptoms. The Pfizer one was much better.” (Fin).
7. INFORMATION	7.1. Disinformation	7.1.1. “Because statistics, as you know, are very malleable, and can also be manipulated to suit the occasion […] no-one had 100% real information.” (Ash). 7.1.2. “Rather than informed, we were disinformed, because of the sheer amount of manipulation, not only of the data but also of the other types of news that they put out… there wasn’t anyone who was very well informed. Nobody knew, neither the mass media, nor the health workers.” (Sage).
	7.2. Changing information	7.2.1. “Do you remember the way that today’s advice was of no use for tomorrow? […] You just didn’t know what to do.” (Oak). 7.2.2. “When AstraZeneca came out, they first said one age; after 3 days they changed the age range completely; then that other age range didn’t seem right to them, and so they changed it again.” (Reeve).
	7.3. Data-sources	7.3.1. “The mass media, which are ultimately the ones that are available to everybody.” (Fin). 7.3.2. “I don’t know, I didn’t trust the typical or mass media excessively, but on the other hand, the alternative information that I found was too alternative. There wasn’t a happy medium.” (Reeve).
8. POLICY-MAKERS	8.1. Late/poor action	8.1.1. “They didn’t know how to manage it. Everything was at the wrong time, we always got there late, it was all sort of chaos.” (Oak). 8.1.2. “They were very slow. They should have closed borders right at the beginning, right when they heard there was a virus. And they’re still managing things badly now, to this day I don’t know why.” (Wren).
	8.2. Understanding	8.2.1. “I think it was something that was just too big for all of us to grasp. Even so, though there were many wrong turns along on the way, they did manage to stabilise the situation to a moderate degree.” (Fin). 8.2.2. “Managing that was very complicated because everything was very new, unfamiliar, and it wasn’t at all easy.” (Wynn).
9. SOCIAL PRESSURE	9.1. Leisure	9.1.1. “Though it wasn’t compulsory as such, there was a time when if you didn’t have it, besides not being able to travel, you couldn’t go into restaurants, bars, discotheques. Granted it wasn’t compulsory but it was a little like legal blackmail.” (Reeve).
	9.2. Work	9.2.1. “There was some pressure, we were somehow between the devil and the deep blue sea. And health workers obviously, they were made to, they had no choice, they didn’t even have to think about it.” (Sage).
10. OTHER NON-COVID VACCINES	10.1. Pro-vaccine	10.1.1“I evidently trust in vaccines, in many of them which are being given, and have been on the market for years.” (Sky). 10.1.2. “Throughout history they’ve saved thousands of lives, from many diseases.” (Reeve).
	10.2. Vaccines received	10.2.1. “Chickenpox, measles and others, chances are you don’t give it a thought. I certainly believe that vaccines are good.” (Noel). 10.2.2. “I had all of those, but I haven’t had a jab since I was 12 or 14” (Reeve).
	10.3. Influenza vaccination	10.3.1. “I’ve never had a flu’ jab in my life, I don’t know whether flu’ is included in the mandatory vaccination for when we’re kids.” (Reeve). 10.3.2. “Personally I’m pro-vaccine and pro-medicine but I’m not having the flu’ jab. But because I don’t usually get ill, I don’t consider it necessary.” (Wynn).

Adverse effects

Adverse effects were cited as the major reason for refusing some of the vaccines against COVID-19. Every FG discussed important gynaecological problems associated with the COVID-19 vaccine. Whether because of cases of women they knew or because of personal experience, participants cited changes in the menstrual cycle or total withdrawal of the period due to the vaccination (quote 1.1.1. and quote 1.1.2.).

Albeit with less concern, practically all the participants reported having suffered mild and transitory effects after vaccination, such as malaise, headache, fever, arm pain (quote 1.2.1.) or inflammation of the lymph nodes (quote 1.2.2.). Participants repeatedly likened these symptoms to those caused by an influenza process (quote 1.3.1 and quote 1.3.2.).

In all the sessions, there were some participants who claimed that they knew of some case or that they themselves had experienced paresthesia after vaccination. All agreed on the fact that it affected the jaw and arm. Participants appeared to have been very shocked by this effect and considered it serious but reported that it had only lasted a few moments (quote 1.4.1. and quote 1.4.2.).

Some participants also disclosed that they knew cases of persons who had suffered from cardiovascular problems (quote 1.5.1. and quote 1.5.2.) or blood clots (quote 1.6.1. and quote 1.6.2.) immediately after having received the vaccine.

Despite the variety of adverse effects described during the sessions, in many cases the participants wondered about whether the possible risks of vaccination outweighed those of COVID-19 (quote 1.7.1. and quote 1.7.2.). Furthermore, various participants displayed scepticism about the adverse effects, making the point that there is no proof that these are effects which derive from the vaccine, and that they might possibly have occurred even if the COVID-19 vaccination had not been received (quote 1.8.1. and quote 1.8.2.).

Vaccine protection

Many participants took the view that the vaccine had been essentially designed to mitigate the severity of the disease, and they evinced uncertainty as to whether the vaccine afforded protection (quote 2.1.1. and quote 2.1.2.). That said however, several participants stated that the vaccines did not halt transmission of the virus and thus did not prevent other persons from becoming infected (quote 2.2.1. and quote 2.2.2.).

Another reason for criticising the vaccines was that, rather than being specific to each strain of the virus, doses of the same vaccine were repeatedly being administered (quote 2.3.1. and quote 2.3.2.).

In general, participants expressed the view that actually having experienced COVID-19 confers fuller, stronger and longer-lasting natural immunity than can be achieved through vaccination (quote 2.4.1.).

Need for vaccines

In all the sessions there was a detectable perception that the current situation was much less dangerous than it had been at the onset of the pandemic. Even so, the participants stated that their vaccination decision could change at any time: if the symptoms became as or more severe than at the outset, then they would get vaccinated (quote 3.1.1. and quote 3.1.2.).

Nevertheless, some participants believed that boosters (third and fourth doses) were necessary for risk groups but in no case for the healthy young population, whom they did not consider to be at risk (quote 3.2.1.). In addition, they made comparisons with the influenza vaccine, which they considered solely necessary for people who presented with some type of risk in relation to the disease (quote 3.2.2.).

Vaccination in children

The possibility of long-term effects was an issue that gave rise to great concern among the participants (quote 4.1.1.). Several of them regretted having vaccinated their children (quote 4.1.2.). In part, this had been due to the fact that there were no specific studies on vaccines for children (quote 4.2.1.) In addition, they felt that children experienced the disease with milder symptoms, even in those cases where they had not been vaccinated (quote 4.3.1.) (quote 4.3.2.).

Pharmaceutical industry

Most participants doubted whether all the stages corresponding to the development of a vaccine had been followed, a process that normally takes far longer (quote 5.1.1.) (quote 5.1.2.) Moreover, they assumed that the pharmaceutical industry is a corporate entity that seeks financial profits (quote 5.2.1. and quote 5.2.2.). Despite this, they acknowledged that it had offered a swift solution to the urgent situation which prevailed in the midst of the pandemic (quote 5.3.1. and quote 5.3.2.).

Differences between COVID vaccines

There were different views about the various vaccines developed against COVID-19. Some participants considered that all the COVID-19 vaccines developed were similar, based on the fact that they all caused the same adverse effects and afforded the same level of protection (quote 6.1.1. and quote 6.1.2.). In contrast, others felt that the AstraZeneca vaccine gave rise to more side-effects, while the Pfizer vaccine showed itself to be the preferred choice in terms of safety (quote 6.2.1. and quote 6.2.2.).

Information

Opinions about information were generally to the effect that statistical data were manipulated in line with prevailing interests (quote 7.1.1.), and that, as a result, the information was not real, but that there had been a continuous bombardment of false and poor-quality information (quote 7.1.2.). In much the same vein, the participants complained that the information and guidelines given to them had changed continuously (quote 7.2.1.). Hence, there was no consensus on how long had to elapse between the different doses, on the appropriate age ranges for each vaccine, and so on (quote 7.2.2.).

As a source of information, a large proportion of the participants used the mass media, newspapers, news bulletins or the Internet, on account of their being within everyone’s reach (quote 7.1.1.). Even so, many of them stated that they did not consider these entirely reliable (quote 7.3.2.).

Policy-makers

Practically all the participants referred to the fact that politicians failed to do a proper job of management during the pandemic, including the vaccination process. They had acted late on a great deal of occasions (quote 8.1.1.). Nevertheless, the participants showed a certain degree of understanding because they acknowledged that it was a totally new and complex situation to manage (quote 8.2.1. and quote 8.2.2.).

Social pressure

Some participants said that they had felt pressured to have the vaccination for the purpose of visiting leisure venues (quote 9.1.1.). There was also pressure for work reasons, especially in the case of health professionals, who felt that they had no choice (quote 9.2.1.).

Other non-COVID vaccines

The immense majority of the participants stated that they were in favour of traditional vaccines for the prevention of infectious diseases. They acknowledged that these had saved many lives (quote 10.1.1.) and that, having been developed with all the necessary tests and trials, were highly effective (quote 10.1.2.). Indeed, they reported having received all the mandatory jabs in the vaccination schedule when they were small children (quote 10.2.1.), without voicing doubts of any kind whatsoever (quote 10.2.2.). Some participants also reported having had certain vaccines in the case of special situations.

All the FGs mentioned the influenza vaccine in particular, about which they expressed doubts. Many of the participants were not sure of the indications for this vaccine (quote 10.3.1.) and confessed that they did not consider it necessary for themselves, since they did not belong to any risk group (quote 10.3.2.).

Discussion

This is the first qualitative study conducted in Spain to address the beliefs and attitudes associated with barriers to vaccination among people who received the complete primary schedule but declined any COVID-19 booster doses. Short-term adverse reactions observed after the primary schedule were the main reason for refusal. In addition to this, doubts about the protection offered by vaccines and the questioning of their necessity in healthy individuals were also prominent. Distrust toward the pharmaceutical industry due to its economic interests also emerged. Furthermore, misinformation and changing messages from authorities, alongside perceptions of poor pandemic management and social pressure to vaccinate, contributed to reinforcing these attitudes. Finally, although participants generally expressed confidence in traditional childhood vaccines, they showed reluctance toward certain specific vaccines, such as the influenza vaccine.

Our results indicate that vaccine-hesitant subjects do not wish to re-experience the same adverse effects as they experienced with the initial doses, or other—as yet unknown—long-term adverse effects. This may indicate that, in some cases, vaccine hesitancy represents a rational response to negative experiences and, therefore, may be amenable to change when appropriate pro-vaccine information is provided [25, 26]. In addition, participants also expressed safety concerns about the vaccine’s speed of development and the possibility that it might not have complied with all the required stages, as compared to that of traditional vaccines which have been on the market far longer and have undergone testing for a period of years [27–29]. These results are in line with those of other studies conducted on both general and specific populations using qualitative and quantitative methodology [13, 15, 30–32]. One of the communication challenges is to convey the fact that COVID-19 vaccines have been tested in clinical trials with extremely large sample sizes and in highly heterogeneous populations [27–29]. Hence, awareness should be raised about the need to consult official and reliable sources, such as the WHO or European Centre for Disease Prevention and Control [33, 34].

The perception of rapid development and doubts about safety can reduce the perceived benefits of the vaccine. Moreover, our results, as in previous studies, indicate that boosters were not considered necessary by those who had already received the complete schedule or who had already had the disease [30, 32, 35, 36]. This may be attributable to the fact that, thanks to their good health status, participants did not perceive a benefit-risk ratio that was favourable to them [37]. Although this attitude would traditionally be classified as complacency according to the WHO SAGE definition, our findings suggest that participants conducted a rational, albeit subjective, cost-benefit analysis based on the changing nature of the pandemic. This hesitancy reflects rather a disconnect between rigid institutional narratives and an evolving clinical reality [38]. Accordingly, once the critical period of the pandemic has passed, the perception of risk diminishes, and educational campaigns and the mass media should therefore lay greater stress on the benefit-risk ratio for healthy patients and a level of collective protection. Over the course of the pandemic, the decision to be vaccinated has thus been changing in line with the epidemiological situation and people’s own perception of risk [2, 39], due to changes in the information disseminated, personal experience of the disease, or implementation of contention measures [40–42]. Participants accept the risk when they believe that the benefit (of not suffering from a very serious disease) is great, but as soon as the severity of the disease lessens, the benefit ceases to be so great, and they therefore no longer accept the risks [2, 39].

When the results of our study are compared against those of previous studies, it is noteworthy that the determinants of indecision are very similar in various settings with political, economic, educational, religious and/or contextual differences. A possible explanation for this phenomenon could be globalisation, responsible for instantaneous communication of all types of opinions and concerns over the Internet [43]. Anti-vaccine movements have exploited the advantages of globalisation to disseminate disinformation about COVID-19 vaccines and propagate fear worldwide [44, 45]. These actions have reduced trust in healthcare authorities and reliable sources, while increasing the tendency to seek health information on Internet. Moreover, the initial lack of recognition or dismissal by health authorities of reported gynaecological side effects after vaccination may have further contributed to the erosion of trust in the therapeutic alliance between patients and health institutions [46]. In order to enjoy credibility, health and political authorities would need to increase trust by being more consistent and coherent in their decisions [35, 47].

Vaccine hesitancy is aggravated by the need for successive doses which can lead to emotional exhaustion and mental overload [48], a phenomenon commonly known as vaccine fatigue [49, 50]. This fatigue refers to specific problems with vaccines such as the perception of physical inconvenience and concern about side-effects or effectivenes. Consequently, individuals may perceive diminishing returns from continued compliance, reducing motivation to adhere to booster recommendations [51]. However, vaccine hesitancy may also arise after a lengthy period of adaptation to COVID-19 related restrictions on and changes in lifestyle, as part of pandemic fatigue [52]. This situation may culminate in emotional strain, erosion of patience, lack of trust in health authorities and recommendations, and prioritization of other concerns, leading to reduced adherence to general public health directives, including vaccination [53].

Implications

The results of this study provide important information for the authorities to bear in mind when it comes to informing the population, recommending transparent, personalized and evidence-based messages, together with social media campaigns that use verified influencers and open dialogues to counter misinformation and restore trust in vaccines. In addition, it is essential to quantify the effect of each factor identified in vaccine hesitancy future quantitative studies in order to design effective interventions that increase vaccination coverage.

Strengths and limitations

This study has advantages and limitations specific to the use of qualitative methodology. The interaction of the FGs themselves made it possible to ascertain factors associated with vaccine hesitancy, something that would not be feasible with any other methodology. Additionally, the study’s online nature allowed for the participation of people from all parts of Spain, thereby covering a wide spectrum in terms of age, geographical origin, educational level and other relevant demographic factors. Moreover, the online nature of the focus groups may have reduced the risk of dominance. The methodology and design used are in line with the COREQ for qualitative studies.

One of the limitations of the chosen methodology lies in its inability to quantify the influence of each factor related to vaccine hesitancy. It does, however, allow for such factors to be examined in depth. Demographic data were not collected, therefore, it was not possible to assess the influence that this variable might have on the observed results. Moreover, our results may well not be generalisable to other countries, due to the differing cultural aspects and initial government policies related to the COVID-19 vaccines. It was also not possible to measure the potential correlation between hesitancy, acceptance, and vaccination literacy [54] Due to the use of snowball sampling, there is a potential sampling bias, as participants who share similar socio-economic contexts, social circles, or ideological perspectives may have been more likely to participate. This limitation may have reduced the heterogeneity of opinions and experiences represented in the thematic findings. Future quantitative studies could address these limitations. The process of developing topics and choosing quotes may have introduced confirmation biases. To minimise these, the most representative quotes were jointly chosen by the research team. Lastly, opinions may have changed due to the continuous progress of the pandemic. That said, at the date of carrying out this study, the epidemiological situation was stable. Author´s own experience/personal circumstances might have influenced interpretation of the data. Reflexivity discussions among the team healped mitigate this.

Conclusions

The results showed that fear of adverse effects and concerns about the risk–benefit ratio were the main reasons for not receiving the COVID-19 booster vaccination. It is essential to invest in communication strategies that move beyond persuasion and instead focus on generating trust through radical transparency about vaccine limitations and a more empathetic acknowledgment of side effects. Such approaches are essential to rebuild the doctor-patient relationship. Further research enabling causal interpretations would also strengthen the evidence base.

Authors’ contributions

Á.P.-C.: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Data Curation, Writing – Original Draft, Writing – Review & Editing, Visualization. A.L-D: Review & Editing, Visualization. FR: Writing – Review & Editing, Visualization. M.T.H.: Writing – Review & Editing, Visualization. AF: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data Curation, Writing – Original Draft, Writing – Review & Editing, Visualization, Supervision, Project administration.M.Z.-C.: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data Curation, Writing – Original Draft, Writing – Review & Editing, Visualization, Supervision, Project administration.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study was conducted in accordance with the Declaration of Helsinki. According to the Galician Clinical Research Ethics Committee, ethical approval was not required for this study. The consent that was obtained from all the participants was informed.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.