Global Declines in Vaccine Confidence from 2015 to 2022: A Large-Scale Retrospective Analysis (preprint)

The latest WHO/UNICEF estimates of national childhood immunisation coverage have revealed the largest declines in routine immunisation uptake globally in three decades. Although the COVID-19 pandemic has contributed to these falls via supply-side disruptions impacting vaccine availability, the extent to which the COVID-19 pandemic has impacted demand-side barriers, such as vaccine confidence, is not yet well understood. Through a large-scale retrospective modelling study, we investigate the extent to which vaccine confidence has changed globally using pre- and post-pandemic data. A total of 165,729 individual interviews across 55 countries as part of nationally representative surveys were conducted between 2015 and 2022. Vaccine confidence is measured using three items that probe perceptions towards the importance, safety, and effectiveness of vaccines. Changes in national-level confidence are evaluated for the sampled populations and within age and sex subgroups via nonparametric tests and a Bonferroni correction is used to adjust study-wide p-values to account for multiple hypotheses. Since the pandemic, perceptions towards the importance of vaccines for children have seen significant decreases in 46 of 55 countries studied, with significant increases found only in China, India, and Mexico. Vaccines are perceived to be less safe in 24 countries, less effective in 28, with only four countries reporting increases in confidence around vaccine safety and five for effectiveness. Among demographic subgroups, a widening gap between older and younger groups is found, with younger groups becoming less confident over time. Declining global confidence in vaccines, particularly among younger age groups, may be contributing to the backslide in routine childhood immunisation uptake. Growing hesitancy among younger age groups should be investigated as a public health priority to better understand confidence among parents.Funding: Data in this study was funded by the European Commission, Africa CDC, UNICEF, and AIR@InnoHK administered by the Innovation and Technology Commission.Declaration of Interest: Within the last two years, HJL was involved in collaborative grants with GlaxoSmithKline, Merck and Johnson & Johnson. HJL has also received other support for participating in Merck meetings and GlaxoSmithKline advisory round tables. Within the last two years, AdF has been funded by the Merck Investigator Studies Program and has performed consultancy work for Pfizer Inc. Within the last two years, LL has been funded by the Merck Investigator Studies Program, GlaxoSmithKline, and Vaccine Confidence Fund, sponsored by Merck and Meta. MISSING AUTHORSEthical Approval: All data used in this study is fully in the public domain at https://www.vaccineconfidence.org/vci/data-and-methodology/.

Identifying Vaccine-hesitant Subgroups in the Western Pacific: A Latent Class Analysis (preprint)

Background: Vaccine hesitancy has seriously compromised the COVID-19 vaccine roll-out across the Western Pacific; nevertheless, evidence-based recommendations that account for the heterogeneity of vaccine-hesitant populations in this region remain lacking. To help design customized vaccine communication strategies, we sought to investigate the profile of the vaccine-hesitant populations in Cambodia, Japan, Lao PDR, Malaysia, Mongolia, Papua New Guinea, Philippines, Republic of Korea, and Viet Nam. Methods: Using 16,408 survey responses from an international survey distributed in 2021 and 2022, we identified hidden subgroups by conducting latent class analysis (LCA) and examined their vaccine acceptance and booster uptake by using Ordinary Least Square (OLS) regressions. Findings: Our LCA approach identified six classes: college students, distrusters of health care providers (HCPs), stay-at-home mothers, the elderly, compliant pragmatists, and general working population. Booster uptake were significantly low in two groups: college students [13 percentage points; 95% CI -0.21 to -0.05] and HCP distrusters [8 percentage points; 95% CI -0.15 to -0.01]; these groups’ acceptance were also similarly low. Stay-at-home mothers’ acceptance and uptake were comparable, but this group took a large portion of vaccine-hesitant people in the Philippines. The profiles of the vaccine-hesitant populations in each country were compared and categorized into four groups, depending on the composition of classes that account for the unvaccination population. Interpretation: The results of this study suggest that drivers of vaccine hesitancy may vary by country and indicate that each country needs a customized strategy that reflects the profile of its vaccine-hesitant population. The proposed recommendations for each country can identify the target population for designing effective vaccine communication strategies.

The effectiveness of conversational AI services on Covid-19 vaccine confidence and acceptance in Thailand, Hong Kong, and Singapore (preprint)

During the COVID-19 pandemic, the emergence of the infodemic and vaccine hesitancy posed a significant challenge to adequate vaccine uptake. In response, conversational AI services such as chatbots have become an increasingly popular tool in the field of health service delivery and communication to increase individuals’ health literacy and vaccination intention. However, few studies have performed a rigorous evaluation of the effectiveness of chatbots as a means of improving vaccine confidence and acceptance. In Thailand, Hong Kong, and Singapore, from February 11th to June 30th, 2022, we conducted multisite randomised controlled trials (RCT) on 2,045 adults with unvaccinated dependent family members who were vulnerable (i.e., seniors) and had been refusing/delaying vaccination, or newly eligible for vaccines (i.e., children). After a week of using multilingual COVID-19 vaccine chatbots, the differences in vaccine confidence - measured by the Vaccine Confidence Index - and acceptance were compared between the intervention and control groups. Factors of vaccine confidence and acceptance were explored. Compared to non-users, a smaller proportion of chatbot users reported a decrease of confidence in vaccine effectiveness in the Thailand child group [Intervention: 4·3% vs. Control: 17%, P = 0·023] and Hong Kong child group [10% vs. 26%, P = 0·034], and of vaccine effectiveness in reducing severe conditions in the Thailand senior group [12% vs. 21%, P = 0·024]. There was no significant change in vaccine confidence or acceptance in the Singapore child group and Hong Kong senior group. Employing the RE-AIM framework, process evaluation indicated strong acceptance and implementation support for vaccine chatbots from stakeholders, with high levels of sustainability and scalability. This study was the first multisite, parallel RCT on vaccine chatbots and reported mixed success in improving vaccine confidence and acceptance among highly hesitant Asian subpopulations. Deploying chatbots as a complement to existing vaccination strategies could identify users’ main concerns for rejecting/delaying vaccination and facilitate a targeted communication and engagement strategy. Trial registration: NCT05424952

Influenza vaccine uptake among children and older adults in China: A secondary analysis of a quasi-experimental study (preprint)

Background: Influenza vaccination is the key to reducing the influenza-related disease burden, especially among high-risk populations. However, influenza vaccine uptake is low in China. This secondary analysis of a quasi-experimental trial in Guangdong Province aimed to understand factors associated with influenza vaccine uptake among children and older people stratified by funding context. Methods: : A total of 225 children (aged 0.5-8 years) and 225 older people (aged 60 years or above) were recruited from three clinics (rural, suburban, urban). Participants were allocated into two groups based on different funding contexts: self-paid group (N=150, including 75 children and 75 older adults) in which participants paid full market price for their vaccination; and subsidized group (N=300, including 150 children and 150 older adults) in which varying levels of financial support was provided. Univariable and multivariable logistic regressions were conducted stratified by funding contexts. Results: : Overall, 75.0% (225/300) of participants in the subsidized group and 36.7% (55/150) in the self-paid group got vaccinated. Older adults had lower vaccination rates than children in both funding groups, while both age groups showed much higher uptake in the subsidized group than in the self-paid group (86.7% vs 53.3% among children; 63.3% vs 20.0% among older people). In the self-paid group, participants living with children (aOR:2.61, 95%CI: 1.06-6.42) or older people (aOR:4.76, 95%CI: 1.08-20.90) having prior influenza vaccination in the same household were more likely to be vaccinated; trust in providers’ advice (aOR=4.95, 95%CI:1.99, 12.43) or effectiveness of the vaccine (aOR: 12.18, 95%CI: 5.21-28.50), and experienced influenza-like illnesses in the family (aOR=46.52, 4.10, 533.78) were associated with higher vaccine uptake in the subsidized group. Conclusions: Older people had suboptimal vaccine uptake compared to children in both contexts and need more attention in future efforts to enhance influenza vaccination. Tailoring interventions to different vaccine funding contexts may help improve influenza vaccine uptake: In self-paid context, measures to motivate people to accept their first ever influenza vaccination may be a promising strategy. In subsidized context, strategies to improve public confidence in vaccine effectiveness and providers’ advice would be useful. Trial registration: ChiCTR2000040048. Registered on November 19, 2020.

Emotional determinants of public responses to the risk of epidemics and pandemics: a systematic review (preprint)

Background: Understanding how people’s emotions influence their health decisions and behaviours at a population level is fundamental to designing effective communication strategies and public health interventions for infectious disease outbreaks. This review identifies relevant research to assess the role of emotional determinants and their impact on public responses to the risk of infectious disease outbreaks, specifically in relation to the uptake of public health interventions. Methods A comprehensive systematic review was conducted exploring the differences in public responses by emotion, infection, outcome and region. A basic consensus approach was followed in which emotional stimuli were categorised as being either pleasant or unpleasant, and predisposing people to bivalent behaviour ( i.e. , approach or withdrawal). All primary research studies published in five global databases between 1988-2019 were eligible for inclusion. Binomial tests (against a test proportion of 0.5 or 50% for each study outcome) were performed using the direction of effect observed in each study, i.e. , either favouring or not favouring intervention uptake. Results A total of 75 studies from 28 different nations were eligible for inclusion in the review. A total of 97 correlations were made between 12 emotions, 10 infectious diseases, and the uptake of seven types of public health interventions. Unpleasant emotions were evoked much more often than pleasant following public health risk communications, with fear and anxiety being the most common. Overall, moderate anxiety-related emotions (worry, anxiety, stress, concern) seemed to be much more significant motivators for public action compared to extreme unpleasant emotions (fear, panic, hopelessness, shame), which had a statistically significantly negative effect on the uptake of public health interventions in several cases. Pleasant emotions (empathy, hope) also showed promise as motivators for public health intervention uptake, but more research is needed to corroborate this. Conclusions The results of this review show that the public’s emotional responses to epidemics in the past 30 years have played a clear role in determining how successful the rollout of public health interventions has been. Emotions need to be considered in crisis communications, and these research findings can help inform communications strategies in the evolving context of the COVID-19 pandemic and future infectious disease outbreaks.

The potential impact of vaccine passports on inclination to accept COVID-19 vaccinations in the United Kingdom: evidence from a large cross-sectional survey and modelling study (preprint)

Background Four vaccines against the novel coronavirus 2019 disease (COVID-19) caused by the severe acute respiratory coronavirus 2 (SARS-CoV-2) have currently been approved for use in the United Kingdom. As of 30 April 2021, over 34 million adults have received at least one dose of a COVID-19 vaccine. The UK Government is considering the introduction of vaccine passports for domestic use and to facilitate international travel for UK residents. Although vaccine incentivisation has been cited as a motivating factor for vaccine passports, it is currently unclear whether vaccine passports are likely to increase inclination to accept a COVID-19 vaccine. Methods We conducted a large-scale national survey in the UK of 17,611 adults between 9 and 27 April 2021. Bayesian multilevel regression and poststratification is used to provide unbiased national-level estimates of the impact of the introduction of vaccine passports on inclination to accept COVID-19 vaccines among all respondents who have not yet had two vaccination doses. Multilevel regressions identify the differential impact of the likely impact of vaccine passports on uptake intent between socio-demographic groups. Gibbs sampling was used for Bayesian model inference, with 95% highest posterior density intervals used to capture uncertainty in all parameter estimates. Findings We find that the introduction of vaccine passports will likely lower inclination to accept a COVID-19 vaccine once baseline vaccination intent has been adjusted for. Notably, this decrease is larger if passports were required for domestic use rather than for facilitating international travel. The impact of passports while controlling for baseline vaccination intent differentially impacts individuals by socio-demographic status, with being male (OR 0·87, 0·76 to 0·99) and having degree qualifications (OR 0·84, 0·72 to 0·94) associated with a decreased inclination to vaccinate if passports were required for domestic use, while Christians (OR 1·23, 1·08 to 1·41) have an increased inclination over atheists or agnostics. There is a strong association between change in vaccination inclination if passports were introduced and baseline vaccination intent: stated change in vaccination inclination is thus lower among Black or Black British respondents (compared to Whites), younger age groups, and non-English speakers. We find notable sub-national trends, for example, that passports could increase inclination among students and Jewish respondents in London compared to those in full-time education or atheists or agnostics, respectively. Interpretation To our knowledge, this is the first quantitative assessment of the potential impact of the introduction of vaccine passports on COVID-19 vaccine intention. Our findings should be interpreted in light of sub-national trends in current uptake rates across the UK, as our results suggest that vaccine passports may induce a lower vaccination inclination in socio-demographic groups that cluster geographically in large urban areas. Caution should therefore be exercised in introducing passports as they may result in less positive health-seeking behaviours for the COVID-19 vaccine (as well as other existing or future vaccinations) and may contribute to concentrated areas of low vaccinate uptake, which is an epidemic risk. We call for further evidence on the impact of vaccine certification on confidence in COVID-19 vaccines and in routine immunisations in wider global settings and, in particular, in countries with low overall trust in vaccinations or in authorities that administer or recommend vaccines. Funding This survey was funded by the Merck Investigator Studies Program (MISP) Research in context Evidence before this study Proof of vaccination has, to date, had limited use in public and private settings for the UK public, such as proof of yellow fever vaccination for international travel to limited destinations, or requirements of Hepatitis B vaccination in some medical roles. Although recent surveys have suggested that the majority of the British public support vaccine passports, we are not aware of any studies assessing the impact that proof of vaccination status for domestic use or for international travel may have on vaccination inclination and thus—perhaps more importantly—on epidemic spread. Added value of this study We conducted a large-scale survey of more than 17,000 members of the UK public to explore attitudes to vaccine passports for domestic and international use. Bayesian methods are used to compute nationally representative estimates of the impact of vaccine passports on change in inclination to accept COVID-19 vaccines and to establish the socio-demographic determinants of vaccination inclination. This study is, as far as we are aware, the first to assess the impact of vaccine passports on vaccination inclination in the UK. Implications of all the possible evidence This study provides novel insights into the potential impact of vaccine passports on COVID-19 vaccine intent in the UK. Although we find that vaccine passports receive popular support in the UK, there exists large variations in their appeal that stratify along socio-demographic lines. Most notably, younger age groups, Black and Black British ethnicities (compared to Whites), and non-English speakers are more likely to express a lower inclination to vaccinate if passports were introduced. Although these groups comprise a relatively small proportion of the UK population, there are crucial issues that these perceptions among these groups cause: notably, that these groups tend to have lower baseline vaccination intent and they cluster geographically. Therefore, since geographic clusters of low vaccination uptake can result in disproportionate increases in required vaccination levels for herd immunity in adjacent settings, we need to exercise extreme caution in public health interventions that may push these areas further away from vaccination. This is especially so if such an intervention will have little overall impact on the majority of the population outside these areas who are already quite willing to vaccinate. Overall, we find that the introduction of passports for either domestic or international use has a net negative impact on vaccination inclination, once we control for baseline vaccination intent. Our findings suggest that vaccination passports may not only yield damaging health outcomes for already marginalised communities: this may lead to further distrust in the government and public health systems and may have negative downstream consequences for other health-seeking behaviours, for example, routine immunisations.

Monitoring global trends in Covid-19 vaccination intention and confidence: a social media-based deep learning study (preprint)

Abstract Background This study developed deep learning models to monitor global intention and confidence of Covid-19 vaccination in real time. Methods We collected 6.73 million English tweets regarding Covid-19 vaccination globally from January 2020 to February 2021. Fine-tuned Transformer-based deep learning models were used to classify tweets in real time as they relate to Covid-19 vaccination intention and confidence. Temporal and spatial trends were performed to map the global prevalence of Covid-19 vaccination intention and confidence, and public engagement on social media was analyzed. Findings Globally, the proportion of tweets indicating intent to accept Covid-19 vaccination declined from 64.49% on March to 39.54% on September 2020, and then began to recover, reaching 52.56% in early 2021. This recovery in vaccine acceptance was largely driven by the US and European region, whereas other regions experienced the declining trends in 2020. Intent to accept and confidence of Covid-19 vaccination were relatively high in South-East Asia, Eastern Mediterranean, and Western Pacific regions, but low in American, European, and African regions. 12.71% tweets expressed misinformation or rumors in South Korea, 14.04% expressed distrust in government in the US, and 16.16% expressed Covid-19 vaccine being unsafe in Greece, ranking first globally. Negative tweets, especially misinformation or rumors, were more engaged by twitters with fewer followers than positive tweets. Interpretation This global real-time surveillance study highlights the importance of deep learning based social media monitoring to detect emerging trends of Covid-19 vaccination intention and confidence to inform timely interventions. Funding National Natural Science Foundation of China.

Determinants of COVID-19 Vaccine Acceptance in Six Lower- and Middle-Income Countries (preprint)

Background: While a vaccine is the only clinical preventive measure to control the infection and mortality caused by SARS-CoV-2 (COVID-19), delayed acceptance or refusal of COVID-19 vaccines may increase and prolong the threat to global public health and the economy. Identifying behavioural determinants is considered a critical step in explaining and addressing the barriers of vaccine refusal, but there is a lack of evidence around COVID-19 vaccine refusal and delay from a behavioural perspective. This study aims to identify the behavioural determinants of COVID-19 vaccine acceptance and provide recommendations to design actionable interventions to increase the uptake of the COVID-19 vaccine in six lower-and-middle income countries.Methods: Taking into consideration the Health Belief Model (HBM), Theory of Reasoned Action (TRA), and other behavioural models, a Barrier Analysis (BA) approach was employed to examine twelve potential behavioural determinants of vaccine acceptance in Bangladesh, India, Myanmar, Kenya, the Democratic Republic of Congo, and Tanzania. In all six countries, at least 45 interviews with those who intended to take the vaccine (“Acceptors”) and another 45 or more interviews with those who did not (“Non-Acceptors”) were conducted, totalling 542 interviews. Data analysis was performed to find statistically significant (a p-value of less than 0.05) differences between Acceptors and Non-acceptors and to identify which beliefs were most highly associated with acceptance and non-acceptance of the behaviour based on estimated relative risk (ERR).Results: The analysis showed that perceived social norms, perceived positive and negative consequences, perceived risk of getting COVID-19, perceived severity of COVID-19, trust in COVID-19 vaccines, perceived safety of COVID-19 vaccines, and expected access to COVID-19 vaccines had the highest association with COVID-19 vaccine acceptance in Bangladesh, Kenya, Tanzania, and DRC. Additional behavioural determinants found to be significant in both Myanmar and India were perceived self-efficacy, trust in COVID-19 information provided by leaders, perceived divine will, and perceived action efficacy of the COVID-19 vaccines. The study also identified important perceptions and beliefs around COVID-19 and its severity, advantages and disadvantages of being vaccinated, and action efficacy of the vaccine to control the spread of the virus.Conclusion: Many of the determinants found to be significant and their level of significance varied from country to country. National and local plans should include messages and activities that address the behavioural determinants found in this study in order to significantly increase the uptake of COVID-19 vaccine across these countries.

Mainstreaming of conspiracy theories and misinformation (preprint)

Parents - particularly moms - increasingly consult social media for support when taking decisions about their young children, and likely also when advising other family members such as elderly relatives. Minimizing malignant online influences is therefore crucial to securing their assent for policies ranging from vaccinations, masks and social distancing against the pandemic, to household best practices against climate change, to acceptance of future 5G towers nearby. Here we show how a strengthening of bonds across online communities during the pandemic, has led to non-Covid-19 conspiracy theories (e.g. fluoride, chemtrails, 5G) attaining heightened access to mainstream parent communities. Alternative health communities act as the critical conduits between conspiracy theorists and parents, and make the narratives more palatable to the latter. We demonstrate experimentally that these inter-community bonds can perpetually generate new misinformation, irrespective of any changes in factual information. Our findings show explicitly why Facebook's current policies have failed to stop the mainstreaming of non-Covid-19 and Covid-19 conspiracy theories and misinformation, and why targeting the largest communities will not work. A simple yet exactly solvable and empirically grounded mathematical model, shows how modest tailoring of mainstream communities' couplings could prevent them from tipping against establishment guidance. Our conclusions should also apply to other social media platforms and topics.

Assessing COVID-19 Vaccine Hesitancy, Confidence and Public Engagement: A Global Social Listening Study (preprint)

Background: To assess global hesitancy, confidence and public engagement towards COVID-19 vaccination.Methods: We collected and manually coded 12886 social media posts mentioning COVID-19 vaccine from five global metropolises with high COVID-19 burden between June and July, 2020. After assessment, 7032 posts were included in analysis. We manually double-coded these posts using a coding framework developed according to the WHO’s Confidence, Complacency, and Convenience model of vaccine hesitancy, and conducted engagement analysis to investigate public communication about COVID-19 vaccine on social media.Findings: Among social media users, 36.4% (571/1568) in New York, 51.3% (738/1440) in London, 67.3% (144/214) in Sao Paulo, 69.8% (726/1040) in Mumbai, and 76.8% (2128/2770) in Beijing indicated that they intended to accept COVID-19 vaccination. With high perceived risk of getting COVID-19, more tweeters in New York and London expressed lack of confidence in vaccine safety, distrust in governments and experts, and widespread misinformation and rumors. Tweeters from Mumbai, Sao Paulo and Beijing worried more about vaccine production and supply, whereas tweeters from New York and London had more concern on vaccine distribution and inequity. Negative tweets expressing lack of vaccine confidence and misinformation or rumors, had more followers and attracted more public engagement online.Interpretation: COVID-19 vaccine hesitancy is prevalent across the world, and negative tweets attract higher engagement on social media. It is urgent to develop an effective vaccine campaign that boosts public confidence and addresses hesitancy for COVID-19 vaccine rollout.Funding: National Natural Science Foundation of China (No. 71874034).Declaration of Interests: We declare no competing interests.Ethics Approval Statement: This study was exempt from ethical review because it examined retrospective, publicly-available data.