Triste Herencia. Joaquín Sorolla. Oil on Canvas. 1899

Read the Reflection, written 23 September 2021, below the following original Transmission.

Originally published in Nautilus on Dec. 9, 2020.

Safe, effective, and available vaccines are the best long-term solution to the coronavirus pandemic.1 So it’s welcome news that two vaccines are poised for distribution, and others will soon be on their way. Preliminary clinical trial data from these two vaccines, made by Pfizer and Moderna, indicate the vaccines are effective at stimulating a strong and long-lasting response against the virus responsible for COVID-19. A recent FDA briefing2 confirmed the efficacy and safety profile of Pfizer’s vaccine, reiterating that the shot was 95 percent effective at preventing COVID-19 after two doses with no serious safety concerns.

This is all good news, but it’s still unlikely that a vaccine will be widely distributed until mid-2021. Supply constraints could cause additional delays.3 In the meantime, health professionals must continue to develop, trial, and improve the therapeutic management of COVID-19, and people must continue to attenuate transmission through social distancing and adherence to recommended public health practices such as wearing a mask and avoiding crowded indoor activities.

Looming over our best efforts, however, is a factor that could derail the campaign to end the pandemic: distrust of vaccines. In a survey of 1,000 individuals in New York City in April 2020, at the height of the epidemic’s first wave, only 59 percent of respondents said they would get a vaccine, and only 53 percent would have their children vaccinated.4 The large public and private investments in developing vaccines need to be matched by investments in laying the groundwork for vaccine acceptance.

Much is at stake. If the vaccination rollout is to succeed, it behooves us to be sensitive to general perceptions about vaccination. COVID-19 vaccination has to be viewed within the broader context of attitudes toward routine immunization. An effective and safe vaccine that stops the pandemic and restores our ability to resume social, educational, and economic activity could improve public attitudes toward science and enhance vaccine acceptance more generally. Issues around public acceptance of COVID-19 vaccination could influence immunization campaigns for years to come.

Vaccine hesitancy in the United States now ranges from narrow concerns about specific vaccines to broad coalitions of “anti-vaxxers” who reject all vaccines. The roots of these sentiments, most without scientific basis, run deep. The continual expansion of vaccines for children (from seven vaccines 40 years ago to 15 today) is mistakenly thought to burden young immune systems. Other factors include suspicion about the financial motives of the vaccine industry, mistrust of scientific evidence and government institutions,5,6 the effect of vaccine vehicles on neurological disorders, and the distrust in vaccines deliberately sown by Russian-linked social media accounts.7 The result: Even though annual flu shots are available at most neighborhood pharmacies, fewer than half of Americans now receive a flu shot each year.8

Reluctance to get vaccinated for COVID-19 is widespread. Only two-thirds of crowdsourced participants (68.2 percent) in a survey of Canadians reported being very likely to voluntarily get vaccinated.9 In Israel, people who had received influenza vaccinations in regular years were more likely to report that they would accept a COVID-19 vaccine, but others were hesitant.10 A nationally representative study in Ireland and the United Kingdom reported vaccine hesitancy for 26 percent and 25 percent of respondents, and resistance for 9 percent and 6 percent, respectively.11 A survey of 450 Americans found that 67 percent would accept a COVID-19 vaccine if one were recommended by the government. Males (72 percent), adults over 55 (78 percent), Asians (81 percent), and college and/or graduate degree holders (75 percent) were more likely to accept a vaccine.12 Other surveys have indicated that 35 percent of Americans would not accept a COVID-19 vaccine even if one were available today.13

Vaccine hesitancy may not be uniform for all age groups. Parents are more reluctant to vaccinate their children than themselves,14 but children have been found to be key spreaders of infection and should arguably be among the priority groups to be vaccinated, especially if the antibody response is weak in the elderly population.

Attitudes toward a COVID-19 vaccine are still evolving. People’s preferences are a function of the perceived safety and efficacy of a vaccine, and the health burden and outcomes related to the disease—both of which could change. The virus may mutate and become less (or more) virulent. An effective therapeutic may depress the perceived need to be vaccinated, since individuals in good health are often willing to risk getting ill and receive treatment rather than get a vaccine. Risk-benefit calculations may be shaped by new information on the long-term respiratory and neurological effects of the virus. People worldwide may develop pandemic fatigue and desire only a return to normalcy.

The perceived risk posed by the infectious agent is a major motivator for vaccination,15 and this works in favor of acceptance of a COVID-19 vaccine. Perceptions of personal vulnerability16 and anticipated regret17 are also correlated with the choice to be vaccinated, and both are likely to be high for this disease. The more effective the COVID-19 vaccine, the more likely people will choose to be vaccinated. Paradoxically, however, this could reduce vaccine uptake over time if the incidence of COVID-19 declines.18 Fear of a disease does not always translate into high vaccination rates, as a study of tetanus in the 1960s showed.19

Widespread vaccination against COVID-19 requires that scientists and healthcare workers go beyond just providing information: The issue is not simply a matter of educating people about the importance of vaccination. A more sophisticated approach is needed to address convenience, affordability, and trust in public institutions.

The first hurdle is engendering confidence in the vaccine development process. The speed at which the first vaccines have been developed could itself prove a barrier to vaccine acceptance. The language of “Warp Speed,” intended to communicate urgency, unintentionally signals a prioritization of urgency over safety. In this context, the commitment of pharma CEOs to “only submit for approval or emergency use authorization after demonstrating safety and efficacy through a phase 3 clinical study that is designed and conducted to meet requirements of expert regulatory authorities such as FDA” inspires confidence.20 The advantages of getting a vaccine to market quickly could be squandered if too many people believe it has been rushed to market without adequate safety and efficacy testing. Time is wasted if they need to be convinced otherwise. Communicating the vaccine’s safety and efficacy is critical. Without this, even healthcare workers may be reluctant to be vaccinated.10

Second, trust in public authorities is likely to be a significant factor.10 People with diminished trust in the country’s leaders are far less likely to accept a COVID-19 vaccine. Public officials, community leaders, celebrities, and their families should themselves get vaccinated and be transparent in a nonlegalistic, commonsensical manner about the risks and benefits. Trusted voices must be used to improve public understanding. The enthusiastic declaration by three former U.S. presidents that they want to be among those receiving the vaccine will hopefully inspire other influencers to step forward.

Third, it is important to find local solutions to vaccine hesitancy. Demographic and geographic disparities in vaccine acceptance could lead to creating clusters of unvaccinated individuals who could then sustain repeated outbreaks of COVID-19. Achieving a high national average vaccination coverage rate would then not be sufficient. A targeted approach to messaging and improving coverage could expedite our exit from the pandemic.

Fourth, mandatory vaccination policies should be avoided because they could backfire. More acceptable would be tying vaccination status to travel or access to public places. Such policies preserve individual agency to reject the vaccine while also protecting public health, much like regulations that prohibit smoking in public places: Individuals can do as they like in private.

Finally, social media should be used to help shape preferences around COVID-19 vaccination and counter those who oppose vaccines under any circumstances. Researchers found that 54 percent of anti-vaccination ads on Facebook came from just two organizations: the World Mercury Project and Stop Mandatory Vaccinations.21 Facebook’s recent pledge to remove discredited claims about COVID-19 vaccinations22 could be a significant step toward countering misinformation from these groups, despite the inherent difficulties around detecting, discerning, and removing misinformation at scale.23

Another study24 found that anti-vaccine groups were small and had few followers but were more likely to be linked into social media of decision-making bodies, such as parent associations at schools. Emotive and fear-based online messages are seeding doubt about vaccines and gaining disproportionate strength over neutral, scientific postings.

There is little time to lose in the campaign to end the pandemic with a vaccine. At least 70 percent of the population must be covered to reach herd immunity, with higher or lower levels in some communities. This is achievable. Mississippi, with strict laws against nonmedical vaccine exemptions for school attendance, has vaccination rates for measles and diphtheria-tetanus-pertussis exceeding 99 percent, and California, Maine, and West Virginia have followed the Mississippi example. Successful vaccination programs are possible in all states, regardless of the political leanings of their residents.

Fresh thinking and behavioral research are needed to build trust and complement authoritative and data-oriented communications. A lot has been written on the importance of known, trusted messengers of information including doctors and nurses, community thought leaders like ministers, or heads of important community groups. However, our existing knowledge base is in the context of childhood vaccines. Trusted voices and strategies to support a potential COVID-19 vaccine need to be identified. Discussions with family and friends can help address people’s concerns, yet this is not part of the current strategy to encourage vaccination.25 There is evidence that traditionally trusted sources like the U.S. Centers for Disease Control and Prevention are seen as less reliable in the context of a COVID-19 vaccine than are doctors and nurses.26 Given the importance of community opinions and social norms, vaccine messaging and engagement should address specific communities known for low vaccination compliance.27 We have a window of opportunity to course-correct to ensure that we have a vaccine that is not just safe, effective, and available but is also trusted. That work should begin immediately.


Ramanan Laxminarayan
Center for Disease Dynamics, Economics & Policy,
Princeton University,
The University of Washington

Susan Fitzpatrick
James S. McDonnell Foundation,
SFI Science Board, 
Washington University, 
Arizona State University

Simon A. Levin
Princeton University,
Center for BioComplexity,
SFI Science Board member

Acknowledgment: We are grateful to the James S. McDonnell Foundation for its support through Princeton University to support a collaborative addressing vaccine hesitancy and other public health issues. We also thank Aditi Sriram at CDDEP for valuable research assistance. Any errors that remain are the sole responsibility of the authors.



1. Leung, K., Wu, J.T., Liu, D., & Leung, G.M. "First-wave COVID-19 transmissibility and severity in China outside Hubei after control measures, and second-wave scenario planning: a modeling impact assessment." Lancet 395, 1382-1393 (2020).

2. Pfizer-BioNTech COVID-19 Vaccine (BNT162, PF-07302048) Vaccines and Related Biological Products Advisory Committee Briefing Document— Accessed Dec. 8, 2020.

3. Sheikh, K. Find a vaccine. "Next: Produce 300 million vials of it." The New York Times (2020).

4. COVID-19 Tracking Survey, School of Public Health. Accessed August 13, 2020.

5. Salmon, D.A., Dudley, M.Z., Glanz, J.M., & Omer, S.B. "Vaccine hesitancy: Causes, consequences, and a call to action." Vaccine 33, D66-D71 (2015).

6. Larson, H.J., Cooper, L.Z., Eskola, J., Katz, S.L., & Ratzan, S. "Addressing the vaccine confidence gap." Lancet 378, 526-535 (2011).

7. Walter, D., Ophir, Y., & Jamieson, K.H. "Russian Twitter accounts and the partisan polarization of vaccine discourse." American Journal of Public Health 110, 715-724 (2020).

8. Flu vaccination coverage, United States, 2018–19 influenza season | fluvaxview | seasonal influenza (Flu) | CDC. Accessed August 25, 2020.

9. Concerns about COVID-19 — A view from Canada — Coronavirus (Covid-19) researches. Accessed August 10, 2020.

10. Dror, A., et al. "Vaccine Hesitancy: The next challenge in the fight against COVID-19." European Journal of Epidemiology 35 (2020).

11. Murphy, J., et al. "Preparing for a COVID-19 vaccine: Identifying and psychologically profiling those who are vaccine hesitant or resistant in two general population samples." PsyArXiv (2020). 

12. Malik, A.A., McFadden, S.M., Elharake, J., & Omer, S.B. "Determinants of COVID-19 vaccine acceptance in the US." medRxiv (2020).

13. Mullen O’Keefe, S. One in three Americans would not get COVID-19 vaccine. (2020).

14. Lima, G., Hwang, H., Cha, C., & Cha, M. "Public willingness to get vaccinated against COVID-19: How AI-developed vaccines can affect acceptance." arXiv (2020).

15. Brewer, N.T., et al. "Meta-analysis of the relationship between risk perception and health behavior: The example of vaccination." Health Psychology 26, 136-145 (2007).

16. Brewer, N.T., DeFrank, J.T., & Gilkey, M.B. "Anticipated regret and health behavior: A meta-analysis." Health Psychology 35, 1264-1275 (2016).

17. Brewer, N.T., Chapman, G.B., Rothman, A.J., Leask, J., & Kempe, A. "Increasing Vaccination: Putting psychological science into action." Psychological Science in the Public Interest 18, 149-207 (2017).

18. Leventhal, H., Singer, R., & Jones, S. "Effects of fear and specificity of recommendation upon attitudes and behavior." Journal of Personality and Social Psychology 2, 20-29 (1965).

19. Frank, K. & Arim, R. "Canadians’ willingness to get a COVID-19 vaccine when one becomes available: What role does trust play?" (2020).

20. Taylor, N.P. "COVID-19 vaccine CEOs vow to wait for phase 3 data before filing for approval." (2020).

21. Jamison, A.M., et al. "Vaccine-related advertising in the Facebook Ad archive." Vaccine 38, 512-520 (2020).

22. Isaac, M. "Facebook says it will remove coronavirus misinformation." The New York Times (2020).

23. Bliss, N., et al. "An Agenda for Disinformation Research. Computing Community Consortium (CCC) Quadrennial Paper" [whitepaper]. (2020)

24. Johnson, N.F., et al. "The online competition between pro- and anti-vaccination views." Nature 582, 230-233 (2020).

25. Chan, M.S., Jamieson, K.H., & Albarracin, D. "Prospective associations of regional social media messages with attitudes and actual vaccination: A big data and survey study of the influenza vaccine in the United States." Vaccine 38, 6236-6247 (2020).

26. Reed, T. "Americans see hospitals as more trustworthy than FDA or CDC on COVID-19 vaccine information, poll finds." (2020).

27. Quinn, S.C., et al. "The influence of social norms on flu vaccination among African American and White adults." Health Education Research 32, 473-486 (2017).

T-036 (Laxminarayan, Fitzpatrick & Levin) PDF

Read more posts in the Transmission series, dedicated to sharing SFI insights on the coronavirus pandemic.


September 23, 2021


Much has been written about vaccine hesitancy since our piece “How to Build Trust in COVID-19 Vaccines” discussed the need for multiple communication strategies if society were to reach the all-important goal of vaccinating 70% or greater of the population. Unfortunately, during 2021, as vaccines became safely produced and made widely available, we have witnessed a hardening of the vaccine/anti-vaccine lines that could have been anticipated and mitigated to some extent as outreach to different communities occurred. For many in the scientific, public health, and medical communities it can be hard to fathom that, with the pandemic dragging on and curtailing daily life, and the emergence of the Delta variant threatening lives and livelihoods, a significant percentage of the US population (45% as of September 23, 2021) remains unvaccinated. The proportions of the unvaccinated around the globe is far greater, but that is largely because of shortage of vaccine supply. For a wealthy country like the United States where vaccines are conveniently available in virtually every neighborhood, the shortfall in vaccination coverage is difficult to explain. Vaccination coverage (fully vaccinated) in the US hovers around 50%;1 rates are higher in France and Germany (64%) and the United Kingdom (67%). Canada is currently reporting that 75% or more of the eligible population is fully vaccinated.

Vaccination coverage in the US is highly skewed, with the greatest uncovered populations in the South and Midwest. Who are the unvaccinated? There is the core set of committed anti-vaxxers, who are not satisfied with rejecting vaccines for themselves but also actively voice their objections to all vaccines and disseminate false or incomplete information to stop others from obtaining recommended vaccines. This group, although small in number, is not receptive to any messaging or debate regarding the benefits of getting a COVID-19 vaccine.

The larger “vaccine-resistant” population is partially a direct product of the political polarization the US and other countries are experiencing. A percentage of the hesitant are skeptical of COVID as a disease and of the need for a COVID vaccine as a remedy. For some, resisting “coercion” from the government or the dictates of coastal elites appears to be a point of pride.

There is a third category of the “vaccine hesitant,” who represent a variety of individuals who are not yet vaccinated because they do not believe they are at risk for the disease, doubt the new vaccine technologies are safe, fear possible side-effects could derail them from home and work responsibilities, or must overcome the inconvenience of seeking vaccination, especially if they live in sparsely populated rural areas. For the hesitant, the right message delivered by the right messengers (trusted medical care or other professionals, employees and coworkers, family, or friends), could sway some individuals. Our bet is that reaching the resistant or the hesitant requires a small-scale, personal, and hyperlocal “carrot”-based approach. Mandates and harsh sticks are likely to fail to be persuasive.

Within the unvaccinated population, there is also a group of people who have not received much attention and could be characterized as the “reluctant.” One of us (SF), on a routine trip to a local drugstore, observed another such customer awaiting her vaccination against COVID-19. She talked rapidly and incessantly, as the anxious tend to do. Her stream of consciousness monologue centered on why she had waited so long. It was early September 2021; she could have been vaccinated months ago. When the vaccinator told her she was done, the customer’s surprised relief that it was over and painless was palpable, revealing a possible reason for her “hesitancy”: a dread of needles.

Like that drugstore customer, many unvaccinated individuals are not committed anti-vaxxers; they neither mistrust vaccines nor disbelieve COVID is causing serious illness and death. Instead, the reluctant are those who fear needles, dislike engaging with the medical system, or procrastinate when it comes to other routine medical interventions such as annual exams or health screens. Lack of adherence to medical advice is a major issue the medical community continually grapples to solve.2

The vaccine reluctant offer the greatest opportunity for increases in coverage essential for the United States to exit the pandemic. Nudges could be helpful, and many have been proposed, including employer mandates or the granting of vaccine passports for highly valued activities. Some individuals could be reached by bringing vaccinators to workplaces, neighborhood stores, shopping centers, social activities (convenient vaccine booths at community events such as fairs, festivals, etc.) or by campaigns to get friends and family members to act as vaccine coaches. Approaches such as vaccine lotteries have had limited effect, most likely because they do not directly address the sources of the reluctance.

The silver lining in the COVID pandemic has been the rapid response of science in helping develop and deploy vaccines at a pace that is unprecedented in history. However, the lack of progress on vaccination holds back everyone, including those who have been vaccinated. Paradoxically, this monumental success of science, public health, and clinical care is somehow deepening a political divide that predates COVID-19.

Unless we take serious measures to close the vaccination gap, conditions for viral mutations and evolution will continue to pose a threat for everyone. We must begin by acknowledging that the lack of confidence in political and other institutions has been building for a while. The current situation is both an opportunity to rebuild in a broader sense and an essential barrier to bringing the country back from the depths of the pandemic. Frustration notwithstanding, treating one another with humanity is still the right way to go.

Read more thoughts on the COVID-19 pandemic from complex-systems researchers in The Complex Alternative, published by SFI Press.

Reflection Footnotes

1 “See How Vaccinations are Going in Your County and State,” The New York Times,

2 “Medication Adherence in America: A National Report Card,” National Community Pharmacists Association,