A study published in Nature Medicine in March 2023 explores the factors associated with so-called “vaccine fatigue”, with a specific focus on the recent vaccination campaigns in response to the COVID-19 pandemic. The authors state that vaccines are “likely to remain one of the essential tools”. We have developed vaccines that are now “widely available in many countries” and progress in vaccine development has been made. However, the authors acknowledge that vaccines can only be effective if people get vaccinated.  

“Unfortunately, several behavioural factors threaten to undercut the advances in vaccine supply and development.”  

Previous studies have identified vaccine hesitancy as an “obstacle” to primary vaccinations and decreasing “enthusiasm” for boosters. The study suggests that “vaccine fatigue” has emerged as a “growing concern for public health officials”. In fact, it implies that this is a re-emergence rather than a unique phenomenon, already familiar from the “influenza context”, where “suboptimal uptake has repeatedly resulted in many unnecessary deaths”.  

“It is very likely that the failure to address vaccination hesitancy and fatigue could have serious public health consequences in the long run and, in turn, increase pressure on healthcare systems.”  

Understanding COVID-19 vaccine fatigue through the study 

The study addresses two “practically and theoretically relevant research questions”.  

  1. Should vaccination campaigns adopt similar or different strategies for primary and booster vaccinations? 
  2. What are the most relevant contextual features and the most effective interventions that may affect vaccine acceptance in future scenarios? 

The aim of the study was to gather evidence for the design of “effective” campaigns in the context of the “heterogeneous immunisation status in the population” and “possible contextual contingencies”.  

The researchers designed two conjoint experiments, which allowed them to manipulate “multiple attributes of a hypothetical scenario” and “measure the responses of participants considering all attributes jointly”. A literature review demonstrated that the most important factors for COVID-19 vaccine uptake were the properties of vaccines, communication, costs/incentives, and legal rules.  

Fatigue and hesitancy 

The authors note that vaccine fatigue, in addition to the challenge presented by vaccine hesitancy, is a “growing concern” for public health due to “waning immunity” and the requirements for booster vaccinations considering new variants. They suggest that in “many countries” the uptake of boosters has remained “below expectations”.  

Although the definitions of vaccine hesitancy and vaccine fatigue remain unclear across literature and media communication, the study refers to both in a “broad sense as an umbrella term”. This term describes a “low or intermediate propensity to get vaccinated either for the first time (hesitancy) or repeatedly (fatigue)”. The term covers those who are “in a state of indecision or uncertainty” but also those who “oppose and refuse vaccination”. However, the authors acknowledge that “more narrow conceptions coexist”.  

The first question 

The first question addressed the approach that should be taken for future vaccination campaigns; should they be a “one-size-fits-all” approach or should “group-specific characteristics” be taken into account?  

The results suggest that distinguishing campaigns between primary and booster vaccinations is the best approach, in line with early pandemic research. However, the study builds on this previous research by showing “additional variation” between those who have not had a first booster and the “triple vaccinated”, suggesting that “further group differences may need to be considered”.  

The results also indicate international differences. For example, the relevance of information on Long COVID mattered more in Austria than in Italy.  

“These patterns underline our first piece of actionable advice that instruments of vaccination campaigns need to be tailored and tested before campaign rollout, taking into account characteristics of the national context and the different target groups based on their vaccination status.”  

The second question 

The second question explored how different groups “can and should” be addressed by campaigns. Although “from a medical perspective” the importance of closing the vaccination gap and focusing on the unvaccinated seems a priority, the authors state that this may be difficult. The unvaccinated score “low on trust in institutions” and are the “least likely to get vaccinated across all scenarios”. The study considers that the countries involved, Austria and Italy, had both considered some type of vaccine mandate during the pandemic, and therefore “most of those who can be reached by vaccination campaigns have already been vaccinated”.  

“Only campaign messages conveying a sense of community and emphasising the need to hold together to overcome the crisis were effective in promoting behavioural change in the unvaccinated group.” 

By contrast, legal rules such as mandates or vaccine passports were found to “undermine” trust in the vaccine. These results suggest that the “most socially agreeable way to encourage primary vaccinations” would be a focus on “promoting community spirit” over “stricter policy interventions”. Furthermore, it is “essential” to address the factors that contribute to vaccine hesitancy, such as mistrust and misinformation.  

People who had been vaccinated once or twice were “strongly encouraged by positive incentives” such as monetary perks, and the availability of new vaccines. The latter was “only marginally statistically significant” but suggests the need to promote “better understand of heterologous vaccinations” and to obtain regulatory approval for new non-mRNA vaccines as boosters.  

Triple vaccinated people 

For those who were triple vaccinated, the authors considered the possibility that incentives and strategies may seem a “superfluous exercise”. It would be easy to act under the assumption that they will go and get the “necessary boosters” under “any circumstances”. However, the results suggest otherwise, with “seemingly trivial costs” presenting an obstacle to the triple vaccinated that might deter them from “translating their positive attitudes into actual behaviour”.  

“We found a high degree of cost sensitivity among the triple vaccinated.”  

This was reported as the “strongest effect” across the experiments and “most consistent” in both Austria and Italy.  

“Cost-free and easy access to vaccines as well as creating awareness of when and how to get the vaccine, therefore, are likely to remain the mainstay for any vaccination campaign to succeed.”  

Other factors that influence the triple vaccinated group are messages emphasising personal health benefits, the importance of “protecting vulnerable peers” and the healthcare system, as well as “community spirit and self-efficacy”. As this group represented the largest population in both countries, failure to “(re)activate and (re)mobilise” them is likely to result in poor booster rates. 

What does the study show? 

The authors conclude that the results present “several actionable points”: 

  • Test the design and instruments of vaccination campaigns with target groups 
  • Keep the cost-free provision of vaccines and easy access to vaccination sites in which even seemingly trivial costs could be strongly discouraging 
  • Promote community spirit and set measures to strengthen social cohesion and institutional trust in the long term 
  • Consider moving from communicative mobilisation to more institutionalised bonus programmes with positive incentives for booster vaccinations in the long term, if budgetary constraints allow 
  • Carefully assess the risks and benefits of stricter policy instruments involving legal requirements, such as vaccine passports and vaccine mandates, which bear a risk of backlash 
  • Facilitate consensus-building among medical professionals and scientists by supporting research and making relevant evidence readily available 

How might these actions be implemented in your community, and do you think will be effective in encouraging vaccine uptake or overcoming vaccine fatigue? We look forward to considering these questions and more at the World Vaccine Congress in Washington next week.