The COVID-19 pandemic plunged the world into an unprecedented health crisis, disrupting societies and straining healthcare systems globally. Australia's first encounter with this disease began with the confirmation of its first COVID-19 case in Victoria on January 25, 2020 (1). Since then, the country reported over 11 million cases and mourned more than 23,000 lives lost (2), underscoring the profound public health toll of this disease.

As COVID-19 transitions from a pandemic to an endemic phase, the insights gained from this period continue to shape public health interventions and vaccination programmes. In response to the urgency of the situation, novel COVID-19 vaccines were developed and swiftly rolled by the Australian government in January 2021 under the COVID-19 Vaccine National Roll-out Strategy, prioritizing distribution based upon population group vulnerability (3, 4). However, the rollout encountered several setbacks that fuelled negative narratives and misinformation in the traditional press and social media spheres, impacting initial COVID-19 vaccine uptake (4, 5).

In April 2021, safety concerns surrounding the government-chosen ChAdOx1-S vaccine were raised, particularly regarding a rare but serious side effect known as thrombosis with thrombocytopenia (TTS) which had higher reported rates in younger adults (6). Due to a higher risk of TTS with the ChAdOx1-S vaccine in younger adults, the BNT162b2 vaccine was instead recommended first for those under 50 years of age (4, 6). However, subsequent revisions in June 2021 increased the age threshold to 60 years, as further evidence emerged of heightened TTS risk among adults aged 50–59 years. Yet, the persistent challenge of limited BNT162b2 supply meant that healthy adults under 40 years remained unable to receive the vaccine until August 2021 in most regions of Australia. This led to negative media coverage and the spread of vaccine misinformation, and this social amplification of vaccine-related risks, may have eroded COVID-19 vaccine confidence among the general public (7).

Vaccine confidence refers to the belief in the effectiveness and safety of vaccines and trust in the systems that deliver them, ranging from no confidence to complete confidence (8). While distinct from vaccine hesitancy (the motivational state of being conflicted about or opposed to getting vaccinated) (8), low vaccine confidence can contribute to hesitancy, impacting the decision to get vaccinated and overall vaccine uptake. Introduced in the early 21st century (9, 10), vaccine confidence emerged in response to growing hesitancy driven by misinformation, such as the debunked link between the measles, mumps, and rubella vaccine and autism (11). The Vaccine Confidence Project (VCP) established in 2010, along with the WHO's Strategic Advisory Group of Experts (SAGE), has been instrumental in studying and mapping vaccine hesitancy globally, identifying key factors such as “convenience,” “complacency,” and “confidence” as reasons for hesitancy (10). The 2022 EU VCP report indicated a decline in vaccine confidence during the COVID-19 pandemic, underscoring the need to understand these trends for future vaccination strategies (12). High vaccine confidence is essential for achieving high coverage and herd immunity, reducing disease transmission, and protecting those who cannot be vaccinated (13). On the contrary, low confidence can lead to outbreaks and prolonged public health crises, making it crucial for public health bodies to foster vaccine confidence to safeguard public health (14).

A recently published single-center, cross-sectional study in Australia conducted following the vaccine advice changes highlighted that vaccine confidence was high in adults who had already chosen to receive a COVID-19 vaccination and demonstrated that an individual's source of information was a key influencing factor (15). In this research, recruitment occurred in a hospital setting by inviting adults to complete a digital survey during the observation period following their vaccination. An eight-item, three-factor measure of vaccination confidence was found to be a reliable way to measure vaccination beliefs among these COVID-19-vaccinated individuals. However, whether this holds true for the general population who may not have yet received a COVID-19 vaccine remains unknown.

The aim of the current study, therefore was to assess vaccine confidence in a general sample of Australian adults (≥18 years of age) following the vaccine rollout changes and confirm the factors influencing vaccine confidence and uptake.

In this study, factors influencing COVID-19 vaccine confidence and uptake in Australian adults (≥18 years of age) were assessed using an online cross-sectional survey following national vaccine rollout changes and negative media controversy. The study found that overall vaccine confidence was low and that less than one-third of respondents had received a COVID-19 vaccine. Use of government websites and HCPs, such as GPs, as sources of vaccine information, and receiving an HCP recommendation for vaccination resulted in higher vaccine confidence and likelihood of vaccine uptake. In contrast, exposure to other sources of vaccine information, such as non-mainstream media and online sources, appeared to undermine confidence and the likelihood of vaccination.

In our previous study at Blacktown Hospital, Sydney, Australia (4 August−14 September 2021; N = 1,053), respondents who had just received a COVID-19 vaccine had high vaccine confidence (mean total score of 33.0), which was to be expected (15). In contrast, this study conducted in the wider population and immediately after the previous study (15–21 September 2021), reported low vaccine confidence (mean total score of 20.0) and poor vaccine coverage (29.7%). This suggests that the vaccine roll-out changes in April and June 2021 and the associated negative media controversy that followed (4), indeed may have been detrimental to COVID-19 vaccine confidence among Australian adults. Multiple studies have demonstrated that media coverage can erode vaccine confidence and contribute to vaccine hesitancy. For instance, Catalan-Matamoros et al. identified a significant inverse correlation between negative newspaper coverage from 2012 to 2017 and childhood vaccination rates in Spain (r = −0.771; p < 0.05) (23). Similarly, Suppli et al. (24) reported a 36% decline in HPV vaccination uptake among girls born in Denmark in 2003 following a surge in negative media coverage. This study further supports the potential harmful effects of media on vaccine confidence and its consequences on vaccination rates.

When assessing predictors of high vaccine confidence (total score >30), similar to our previous study (15), the use of government websites as sources of vaccine information was identified as a positive predictor, confirming the importance of utilizing trusted sources, such as government health bodies and HCPs, to disseminate vaccine information. Respondents in our current study who used these sources to access vaccine information were up to six times more likely to have high vaccine confidence and up to eight times more likely to receive a COVID-19 vaccination (Table 2 and Supplementary Table S2, respectively). Furthermore, respondents who were recommended by an HCP to receive a COVID-19 vaccine were almost three and two times more likely to have high vaccine confidence and receive a vaccination, respectively. Similar findings were reported in a recently published UK cross-sectional survey study (16–31 July 2021; N = 4,428) which highlighted that the use of NHS and government websites, and GPs for COVID-19 information were associated with a positive vaccination status (25). The sharing of vaccine information via trusted sources, such as government and health agencies or non-profit organizations, is essential, particularly during disease outbreaks. However, a study of COVID-19 vaccination websites from 58 countries found that only two met the recommended readability level for public materials (26). Similarly, in another study of 23 government websites, just 65% of these sites provided specific communication channels for COVID-19-related inquiries (27), underscoring the need to enhance the effectiveness and frequency of government communications on healthcare and vaccination.

Equally important is the exposure to untrusted information sources and the impact of misinformation. In this study, the use of non-mainstream media and online sources negatively impacted vaccine confidence and reduced the likelihood of COVID-19 vaccination by ~60%. Similarly, self-reported exposure to fake news was found to be a negative predictor of high vaccine confidence and vaccine uptake on univariate analyses. However, this was no longer significant following multivariate analyses likely due to the high proportion of respondents (77.3%) reporting exposure to fake news and the survey being conducted on a social media platform where misinformation is rampant. In our previous study at Blacktown Hospital, fewer respondents reported being exposed to fake news or misinformation (57.5%) but exposure appeared to decrease the likelihood of high vaccine confidence by almost 30% (OR 0.71; 95% CI 0.52–0.96) (15). Similarly, in a randomized controlled trial in the UK and USA (7–14 September 2020; N = 8,001), recent exposure to misinformation reduced the intent to accept a COVID-19 vaccine by 6.2 and 6.4 percentage points, respectively (28). Misinformation that used scientific messaging and imagery was found to be more strongly associated with declines in vaccination intent. Emerging research on theory-informed debiasing interventions, such as debunking, show promise in combating misinformation (29). These interventions should be tailored specifically to address vaccine misinformation, as this research is crucial for managing future pandemics.

For those respondents who had received a COVID-19 vaccination, the top three key reported motivators were to protect one's own health, family/friends, and/or the community (57.4%−76.6%), and were identical to our previous study at Blacktown Hospital (15). Interestingly, female respondents were more likely to be motivated to get vaccinated by the notion of altruistic notions of protecting others, while working adults (< 65 years of age) were more motivated by the prospect of returning to work and protecting their colleagues. While the notion of workers wanting to return to their routine life following lockdowns seems more obvious, gender differences in vaccine motivations are less so. A 2021 systematic review by Zintel et al. (30) found that males were more likely to be motivated than females to receive a COVID-19 vaccine and this difference was greater among healthcare workers compared with the general population. Although our current study did not specifically seek to explore gender differences, post-hoc analyses did indeed reveal differences in mean vaccine confidence levels and vaccination rates between males and females (p < 0.05 for both, results not presented). Potential gender discrepancies in vaccine confidence and motivators for uptake should be considered when implementing immunization programmes and further studies specifically designed to explore this concept are warranted.

This study made use of an eight-item scale to assess vaccine confidence and offered an efficient measure of adult vaccination beliefs. The scale, adapted from Gilkey et al.'s (19, 31) scale developed in parents of adolescents, and initially tested in our previous study at Blacktown Hospital (15), was further validated in this study of adults from the general population. Predictive validity was demonstrated with a one-point increase in total vaccine confidence score associated with a 34% increase in the likelihood of COVID-19 vaccination and multivariable analyses revealed identical positive and negative predictors for vaccination status as for high vaccine confidence. Face validity tests further highlighted that those who had already received a COVID-19 vaccination did indeed have higher overall mean vaccine confidence and subscale scores than adults who had not received a vaccination. The vaccine confidence scale also demonstrated good construct and internal consistency, with three-factor scale confirmatory factor analysis results revealing good model fit (CFI = 0.99; RMSEA = 0.071; X²(17) = 57.2, p < 0.001) and acceptable reliability (α = 0.93). The results were similar to our previous study at Blacktown Hospital of adults that had already received a COVID-19 vaccination, which also showed good model fit [CFI = 0.97; RMSEA = 0.071; X²(17) = 105.9, p < 0.001] and internal consistency (α = 0.82) with the adapted Vaccine Confidence Scale (15).

Several scales have been developed to measure vaccine confidence, and most highlight similar findings: perceived benefits of vaccines are strong predictors of vaccination behaviors (15, 32, 33). Some scales, like those used by Kranzler et al. (32) and MacEwan et al. (33), found that the benefits, such as community protection and minimal side effects, as key predictors. Others, like Luyten et al.'s (34), suggest that risk aversion may also influence vaccine decisions. However, in our study, trust (OR 8.36; p < 0.001) emerged as an especially significant predictor, surpassing perceived benefits and harms (OR 6.59; p < 0.001 and OR 4.36; p < 0.001, respectively). This indicates that, while vaccine campaigns should focus on promoting vaccine benefits and disease risks, they must also come from trusted sources to effectively impact vaccine confidence.

Although this study assessed determinants of high confidence and uptake for COVID-19 vaccines, the results may also apply to other adult vaccines, such as influenza. A recent US cross-sectional survey study that compared predictors of influenza (n = 1,136) and COVID-19 (n = 1,131) vaccine confidence, found that positive attitudes toward vaccination for both were driven by perceived virus severity, vaccine efficacy and adverse effects (35). Similarly, misinformation was negatively associated with the attitudes toward both vaccines. However, some differences are likely present and future research exploring these nuances could provide a deeper understanding of vaccine confidence and uptake drivers across different vaccines.

To our knowledge, this study is the first to cross-validate an adult Vaccine Confidence Scale using COVID-19 vaccines across different settings and by vaccination status (15). Although the study contributes valuable insights into the factors associated with high vaccine confidence and the motivations for receiving a vaccination, several limitations should be noted. (1) As a cross-sectional and observational study, it cannot establish causal relationships. Longitudinal data are needed to determine if predictors of high vaccine confidence persist and if they apply to booster doses of vaccines. (2) The study was conducted in Australia only, which may limit the generalizability of the findings. (3) Only Facebook was used to distribute the survey. Although it remains the most widely used social media platform in Australia, as not all individuals use Facebook there is a potential for sampling bias. However, several peer-reviewed studies show that surveys administered via Facebook have minimal bias compared with traditional surveys (36–38). (4) Although all analyses were conducted with complete data, item nonresponses (24.8%) may have led to non-response bias. (5) The type of COVID-19 vaccine received was not assessed, which could influence vaccine confidence, although access to alternative vaccines was limited at the time, with most participants likely receiving the BNT162b2 vaccine. Additionally, the study did not capture the history of other previously received vaccines, potentially leading to residual confounding. (6) Similarly, the state where respondents were from was not captured and state differences in vaccine confidence may exist, depending on state-provided health and vaccine information methods. Further research into regional and demographic differences in vaccine confidence is warranted and may help to support the development of more effective public health interventions with tailored communication strategies to support vaccine uptake.

In September 2021, COVID-19 vaccine confidence was low among adults in Australia likely due to the changes to the national vaccine roll-out strategy and surrounding negative media at the time. Individuals who received vaccine information from government health sites were up to six times more likely to have high vaccine confidence and up to eight times more likely to receive a COVID-19 vaccination. While the use of non-mainstream media and online sources undermined vaccine confidence and reduced the likelihood of vaccination by around 60%. The Vaccine Confidence Scale validated in this study shows promise as a tool for quickly assessing vaccine confidence and predicting the likelihood of vaccine uptake. Further efforts should be placed on increasing the awareness of trusted sources of vaccine information and public health interventions and immunization programmes should consider the use of vaccine confidence tools to optimize communication strategies and support vaccine uptake.