Introduction

Although the COVID-19 pandemic is widely considered to be over, vaccination remains the crucial tool to protect people from severe disease. Notwithstanding adequate supply, vaccine uptake varies considerably among countries and segments of society. For example, as of 30 June 2023, uptake of the primary course of vaccines in Europe ranged from 21.1% in Kyrgyzstan to 92.6% in Spain, and in the U.S. uptake is far higher among Democrats than Republicans with the gap exceeding 30% in some surveys. There were many reasons for low uptake, varying from country to country; however, a sizeable number of people across the globe chose not to get vaccinated. This hesitancy, much of it propelled by disinformation, has also spilled over into childhood vaccinations, with a notable decrease in confidence in 52 out of 55 countries polled by the United Nations International Children’s Emergency Fund (UNICEF). Evidence-informed strategies for addressing low vaccine uptake are thus urgently required.

Focusing on those who make a decision not to vaccinate, we provide a toolbox of possible behavioural and communication interventions that are built on the recognition that vaccine hesitancy may arise from diverse psychological factors that require distinct interventions. We structure our interventions around the 7 C framework1, which assesses vaccine hesitancy along the factors of confidence, complacency, constraints, calculation, collective responsibility, compliance, and conspiracy. Table 1 summarizes the 7 C framework and the corresponding interventions, informed by learnings from the COVID-19 vaccine rollout during the last 2 years, and points to sources with advice to practitioners. Although the relative importance of the various factors in the 7 C framework may differ between vaccines, cultural contexts, and populations, we consider the interventions available for each factor to be relatively stable. Box 1 illustrates how those recommendations can be put into practice in a stylized conversation with a patient. Although we emphasize the learnings from the pandemic, our interventions are broad and can apply to many contexts in which people are hesitant about being vaccinated.

Table 1 Components of vaccination readiness according to the 7C model with suggested interventions for health authorities to improve vaccine acceptance.
Full size table

While psychological factors are the focus of this paper, we acknowledge that low vaccine uptake is complex and multifactorial, and effective solutions to address it often involves interventions that address both individual, social, cultural and structural factors.

Confidence

Confidence refers to “trust in the safety and effectiveness of vaccinations, the health authorities, and the health officials who recommend and develop vaccines”1. Physicians are one of the most trusted sources of health information and even individuals with low vaccination readiness consider their health care providers (HCPs) to be the most trusted source for vaccine information. Ensuring vaccination readiness among HCPs is thus crucial both in terms of increasing their own vaccine uptake to reduce the burden of disease, but also given their role in promoting vaccination in their communities. One way to overcome low levels of vaccination readiness is trying to understand reasons for individuals’ concerns by asking open questions, using reflective listening, and building a trusting relationship during conversations2. The critical role of HCPs underpins the need for effective capacity building and training around such vaccine communication skills. Learning materials that provide guidance for HCPs to apply these skills in conversation are provided by WHO and other organisations (Table 1).

Trust in institutions is another component of confidence and a crucial determinant of vaccine uptake, and trustworthiness of institutions must be maintained by transparent communication. Although one might fear that disclosing negative information may increase vaccine hesitancy, studies conducted during the pandemic suggest that transparent communication sustains trust in health authorities and hinders spread of conspiracy beliefs.

Complacency

Complacency is defined as reluctance “to get vaccinated due to low perceived risk of infectious diseases”1. Perceived risk of the disease is known to be a particularly important factor underpinning vaccination readiness, and this was the case for COVID-19 as well3. Notwithstanding public health messaging and guidelines recommending vaccination for prevention of severe infectious diseases, experiencing no or only mild symptoms can lead people to underestimate the danger of a virus and hence the utility of the vaccine. One way to make possible serious consequences more tangible is through the communication of narratives. Those narratives must however avoid creating fear without also increasing perceived self-efficacy. For further resources on how to communicate individual case reports and still have a critical evidence-based dialogue, see Table 1.

Constraints

Constraints in this context refer to “psychological hurdles that make vaccination difficult”1. Reduced access to trustworthy information has been a critical constraint for many, and various studies have shown that low vaccination rates among ethnic minorities are often not primarily due to anti-vaccination beliefs or ideology, but to a lack of transparent and accessible information. The European Centre for Disease Prevention and Control (ECDC) provides guidance on how to adapt scientific results to different cultural realities, and UNICEF provides information materials on how to make risk communication more accessible to marginalised and vulnerable groups, such as persons with disabilities, indigenous populations, refugees, or children (Table 1). In some cases stress or workload may impair people’s ability to think about a vaccination decision. This can be addressed, for example, by making people aware of stress coping strategies – some useful insights are provided by the Centers for Disease Control and Prevention (CDC; Table 1).

Calculation

Calculation refers to the “degree to which personal costs and benefits of vaccination are weighted”1. The actual availability and quality of information as well as the individual ability to obtain or understand health information (health literacy) can affect this factor. A qualitative study in Australia amongst vaccine-hesitant adults made 11 recommendations to address communication content, delivery, and context to increase uptake and acceptance of COVID vaccines. The recommendations include the need to communicate about vaccine safety and effectiveness (and weigh risk), to address concerns about expected side effects, highlight benefits of vaccination and discuss disease severity to counter a ‘wait and see’ approach and to communicate about vaccine availability.

A wide-ranging comparison of possible interventions in the UK found that messages centreing on the personal benefit accruing from COVID-19 vaccinations were highly effective and increased readiness more than, for example, information on collective benefits4. These results support the idea that people engage in, and are sensitive to, a personal risk calculus, although in other cultural contexts people are also sensitive to collective risks and benefits. A personal risk calculus is important as some people may believe that a vaccine is riskier to them individually due to their health condition, age, or other factors, such as fertility, pregnancy and breastfeeding. People understandably like information to be personalized to their risks and needs.

Information that takes individual differences in health literacy into account is critical to the dissemination of scientific information. Studies indicate that information that is more complex and less comprehensible is less likely to be shared5. Several decision aids provide an instrument for making risk calculations available to laypersons in a comprehensible form, which can contextualise and support decisions about whether to get a vaccine or oneself or one’s child. One example of a decision aid was provided by the National Centre for Immunisation Research and Surveillance (NCIRS) in Australia (Table 1).

Collective responsibility

Collective responsibility is defined as “willingness to protect others and to eliminate infectious diseases” through collective action1. Collective responsibility is an essential ingredient to any vaccination programme because vaccines benefit both the vaccinated and those around them, and if enough people are vaccinated, herd immunity may be achieved. A decision to get vaccinated is therefore a prosocial decision6, which is also reflected by correlations of vaccination readiness with the prosocial personality traits of honesty-humility and agreeableness1.

Consistent with this reasoning, it has been demonstrated that providing information about herd immunity in the case of COVID-19 increases COVID-19 vaccination intentions, which is increased further when inducing empathy for persons who are particularly vulnerable to the disease. Guidance documents on how to build empathy and simulations to communicate herd immunity are available (Table 1). Relatedly, stressing the societal benefits of high uptake rates achieved through vaccination mandates decreased psychological reactance (i.e., anger) towards such policies.

Compliance

Compliance is defined as “support for societal monitoring and sanctioning of people who are not vaccinated”1. Social and cultural norms, and religious, family, and community influence have been found to be important determinants for routine, influenza, and COVID-19 vaccination alike. Existing positive social norms could therefore be leveraged to increase vaccine uptake, such as communicating the scientific consensus on vaccination. A recent study in the Czech Republic demonstrated that communicating such consensus indeed increased COVID-19 vaccine uptake rates x. The communication materials that were used to achieve this effect are publicly available (Table 1).

To enhance uptake, many countries have introduced mandates. These were largely supported by HCPs with the caveat that they should be implemented with careful planning and consultation to avoid unintended consequences. A recent analysis has shown that mandates are quite effective overall at increasing uptake of the mandated vaccine. There are, however, other consequences to mandates such as disgruntlement that may have long-term adverse consequences7. Reactance to COVID-19 vaccination mandates has been observed in studies in Germany and the U.S. The longer lasting negative impact of mandates on vaccine trust and confidence as well as social polarization remains to be evaluated8.

Conspiracy

Endorsement of conspiracies is a strong predictor of vaccination hesitancy9. The continuously evolving and sometimes shifting scientific findings during the pandemic have provided fertile ground for conspiracies. Priority approval procedures for vaccines and the use of relatively new vaccine platforms have added to this perceived capriciousness of scientific knowledge, fuelled further by disinformation, undermining confidence in vaccine safety. Health care professionals may themselves also be susceptible to COVID-19 conspiracy theories.

A strong association between perceived believability of COVID-19 misinformation and low vaccination readiness has been reported in a survey spanning 40 countries10. In addition, randomized controlled trials reveal that exposure to COVID-19 vaccination misinformation can increase the belief in false statements (e.g., vaccination causes cancer) and decrease the intention to get vaccinated11.

Several interventions have shown promise in combating misinformation. For example, choosing trusted messengers can increase COVID-19 vaccination readiness in target groups. Likewise, inoculation messages that explain to audiences how they might be misled before the misinformation is encountered have been repeatedly shown to be effective. Videos that have been proven to produce such inoculation effects are publicly available (see Table 1; the table also provides resources on how to debunk misinformation using a fact-sandwich structure in communication and how to rebut misinformation in public debates).

Conclusions

The COVID-19 vaccines are a scientific and public health success story12, having prevented an estimated 20 million deaths within a year of their introduction. Nonetheless, suboptimal vaccine uptake remains a challenge in many countries globally. Separate to access barriers, a considerable body of behavioural research has emerged related to the psychological factors associated with vaccine hesitancy. The 7 C theoretical framework helps to understand hesitancy towards COVID-19 as well as vaccine hesitancy more widely. This research also produced evidence-informed interventions that can help increase vaccine uptake, separate to addressing access barriers. Those interventions are summarized in Table 1 and provide a broad toolbox that can address the various drivers of hesitancy beyond the specific context of COVID-19.