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The Vaccine Optimism Effect: Why Vaccine News Might Reduce Social Distancing

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May 11, 2021

The third wave of the COVID-19 pandemic has struck with absolute ferocity, leaving many countries straining to cope under the pressure of exponential viral spread. Containing this spread has called for societal cohesion on a huge, unprecedented scale. Globally, citizens have been asked to abide by relatively novel social distancing and stay-at-home recommendations. Such requests, alongside the constantly shifting nature of government restrictions and public health advice, have left many grappling with “pandemic fatigue,”1 where their depleted self-control resources mean that they are much less likely to comply with the recommended pandemic mitigation strategies.

Yet, with the continued success of global vaccination rollouts and consequent easing of lockdown restrictions, pandemic fatigue may be on the decline as people gradually regain some sense of normalcy in their lives. Indeed, promising early data on the successes of current vaccination campaigns has instilled a vestige of hope in people of a long-awaited end to the pandemic.2 However, set against this atmosphere of renewed hope is yet another behavioral bias with potentially catastrophic, pandemic-prolonging effects.

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Two plausible (and antagonistic) reactions to vaccination 

One might suppose that the promise of being vaccinated would steel people against any behavior that might increase their risk of infection. Logically, the prospect of getting vaccinated means that behaving more carefully now would not only delay infection of oneself or others, but could prevent it entirely. People would only have to make one last effort to avoid infection to fortify themselves against any chance of infection and thus ensure their own health and safety— which, given how social distancing and other preventive behaviors have become the “new normal,”3 would simply require people to exercise that little bit more patience. 

Yet, as a vast expanse of the decision science literature points out, humans are not exactly the best logicians. In fact, at a time where abiding by public health guidelines arguably matters the most, our indulgence in our own psychological lapses may negate even the most comprehensive vaccination efforts. 

Well-documented in the behavioral science literature is the fact that the way that we approach risk is predictably and drastically altered by our psychological state. For example, a seminal study by Yuen and Lee4 demonstrated that people in a depressive mood state were significantly more likely to make cautious decisions when faced with hypothetical dilemmas, such as a choice between living with a severe heart ailment or undergoing a potentially life-saving — but risky— medical operation. 

By contrast, individuals who were in a happy mood were more likely to make the risky choice (i.e., to choose to undergo the operation). Therefore, our pathological mood states can dramatically influence our risk-taking tendencies—a notion with potentially significant implications in the COVID-19 era.

Unrealistic optimism in the COVID-19 era 

Evidently, media coverage of COVID-19 has been disproportionately focused on pessimistic content, which has left many people grappling with elevated levels of anxiety and hopelessness.5 More recent news about successful vaccination campaigns may therefore stand in sharp contrast to prior, more psychosocially-distressing headlines, possibly instilling a renewed sense of hope and optimism amongst citizens globally. But there’s a drawback: if such optimism makes people less worried about the pandemic, might this subsequently make them less likely to practice social distancing? 

A recent study6 by Andersson and colleagues at the Research Institute of Industrial Economics demonstrates precisely this pattern of optimism-induced recklessness.6 In their survey experiment, the researchers had half of the participants read information about the availability and effectiveness of current U.S. vaccination programs (e.g., “studies show that several vaccines have over 90% effectiveness, which is much better compared to vaccines against the seasonal flu”). The participants then completed a series of questionnaires about their intentions to abide by social distancing and stay-at-home rules. 

In the control group, the sequence of questionnaire completion was flipped, with participants answering the questionnaire before receiving the vaccine information. Thus, the manipulation allowed an elegant interpretation of whether vaccine information would causally impact those behaviors that are key for slowing the spread of the virus. 

Overall, learning about vaccines has a significant and detrimental effect on people’s health behaviors: the experimental participants reported significantly lower intentions to stay at home and social distance compared to the control participants. 

What could explain such a disparity in pandemic-related dispositions among the participants? Consistent with prior findings on the behavior-influencing effect of our everyday mood, it seems that unrealistic optimism (rather than pandemic fatigue) was to blame. Specifically, when asked to estimate the remaining duration of the pandemic, participants in the experimental (versus control) group gave much shorter estimates. Put simply, people who had learned about upcoming vaccines were more likely to think that the pandemic would be over sooner, and that life would soon return to normal—an unrealistically optimistic state of mind that potentiated their reckless behavior. 

Overall, these results illustrate how our behavioral dispositions can be dramatically influenced by the prevailing context. Insofar as our vaccination perceptions are clouded by a sense of unrealistic optimism, our resultant behavior may reflect a false reality in which COVID-19 is no longer a huge public health concern.

Is the vaccine optimism effect propelling a new wave of infections? 

If some premature optimism about the prospect of vaccination “frees” people to avoid their responsibility to social distance, this may partly explain why many countries—especially those in which vaccine rollouts are in their relative infancy—are facing seemingly insurmountable challenges in curbing a new wave of COVID-19 infections. 

This revelation is hugely important because it is at odds with rational models of forward-looking behavior, which predict that social distancing would increase amongst those anticipating vaccination.7 Yet, people seem to behave less carefully when they expect to become vaccinated, not more. Therefore, our behavioral idiosyncrasies, combined with the looming threat of new and constantly evolving variants, may provide fertile ground for the coronavirus to stake an enduring claim on humanity as we know it. 

Where do we go from here? 

The vaccine optimism effect has potentially huge public health and policy implications. Though a natural and reasonable cause for celebration, successful vaccination campaigns may potentiate riskier pandemic behavior. As the effectiveness of any pandemic-related policy hinges on the compliance of citizens, it may not suffice for governments and policymakers to provide simple social distancing recommendations if these might be easily disregarded as a function of people’s poor psychological motivations. 

Moreover, the powerful influence of social norms8 means that this optimism-induced recklessness runs the risk of becoming a self-fulfilling prophecy. As Reicher and Drury note in their BMJ article9 on the practicality of non-adherence during the pandemic, “If we believe that the norm is to ignore the rules, it may lead us to ignore them too.” Therefore, the very real chance of unrealistic optimism within the public, and its resultant detrimental effects on behavior, might call for stricter government restrictions vis-à-vis social distancing and other key health behaviors. 

Yet, whether stricter measures are warranted is contentious and may be reasonably met with public resistance, as citizens may naturally expect restrictions to ease following widespread reports of successful vaccine rollouts. When evaluating policy scenarios, then, two recommendations are in place. 

First, governments should tailor their vaccine communications more cautiously so as to avoid instilling unrealistic optimism amongst the public. Strong reminders to the public not to let their guard down and to continue following social distancing and mask-wearing recommendations may be necessary. 

Second, when disseminating news about current immunization programs, an important caveat should be highlighted—namely, that full protective immunity is not achieved immediately after vaccination, 10 and so continuing to take extra precautions is necessary. Overall, distinguishing injection from protection may be critical to avoid instilling unrealistic vaccine optimism in individuals. 

All of this notwithstanding, what may be even more important is to recognize our innate psychological lapses and to exert conscious effort to overcome them. Realizing that we may be predisposed towards being falsely optimistic about an end to the pandemic (which may not be nearly as imminent as current vaccine successes make it out to be),11 it is only sound that the notions of prevention and protection continue to be a top-of-mind priority. 

Ultimately, inasmuch as social distancing and other pandemic mitigation regulations implemented in the past year have been both economically and psychologically costly, we risk prolonging their cost should we further indulge in our own psychological frailties.


  1. Zerbe, K. J. (2020). Pandemic Fatigue: Facing the Body’s Inexorable Demands in the Time of COVID-19. Journal of the American Psychoanalytic Association, 68(3), 475–478.
  2. Krammer, F. (2020). SARS-CoV-2 vaccines in development. Nature, 586(7830), 516-527.
  3. Martínez, D., Parilli, C., Scartascini, C., & Simpser, A. (2021). Let’s (not) get together! The role of social norms on social distancing during COVID-19. PLOS ONE, 16(3), e0247454.
  4. Yuen, K. S. L., & Lee, T. M. C. (2003). Could mood state affect risk-taking decisions? Journal of Affective Disorders, 75(1), 11–18.
  5. Hacimusalar, Y., Kahve, A. C., Yasar, A. B., & Aydin, M. S. (2020). Anxiety and hopelessness levels in COVID-19 pandemic: A comparative study of healthcare professionals and other community sample in Turkey. Journal of Psychiatric Research, 129, 181–188.
  6. Andersson, O., Campos-Mercade, P., Meier, A., & Wengström, E. (2021). Anticipation of COVID-19 Vaccines Reduces Social Distancing (IFN Working Paper No. 1378). Research Institute of Industrial Economics.
  7. Makris, M. & Toxvaerd, F. (2020). Great Expectations: Social Distancing in Anticipation of Pharmaceutical Innovations (Cambridge Working Papers in Economics 2097). Faculty of Economics, University of Cambridge.
  8. Bonnell, C., Michie, S., Reicher, S., West, R., Bear, L., Yardley, L., Curtis, V., Amlot, R, & Rubin, G. J. (2020). Harnessing behavioral science in public health campaigns to maintain ‘social distancing’ in response to the COVID-19 pandemic: key principles. Journal of Epidemiology and Community Health, 74, 617-619. 10.1136/jech-2020-214290.
  9. Reicher, S., & Drury, J. (2021). Pandemic fatigue? How adherence to covid-19 regulations has been misrepresented and why it matters. BMJ372, n137.
  10. Center for Disease Control. (2021, April 28). Key Things to Know About COVID-19 Vaccines. Retrieved from
  11. Stankiewicz, K. (2021, January 6). Dr. Scott Gottlieb: Getting Covid vaccine doesn’t mean people can just return to pre-pandemic life. CNBC. Retrieved from

About the Author

Natalie Tham

Natalie Tham

Natalie Tham is a Marie Skłodowska-Curie Early Stage Researcher and is currently pursuing her PhD in digital behaviour change interventions at Trinity College Dublin. Her current interests lie at the intersection of behavioural science and health psychology, though her research spans across the domains of moral psychology, experimental economics, and social psychology. More broadly, she hopes to use behavioural science to improve individual wellbeing and enhance societal cohesion. Natalie holds an MSc (Distinction) in Applied Psychology and Economic Behaviour and a BSc (First Class Honours) in Psychology, both from the University of Bath.

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