ARTICLES https://doi.org/10.1038/s41562-021-01056-1 Measuring the impact of COVID-19 vaccine misinformation on vaccination intent in the UK and USA Sahil Loomba 1,5, Alexandre de Figueiredo 2,5 ✉ , Simon J. Piatek2, Kristen de Graaf2 and Heidi J. Larson 2,3,4 ✉ Widespread acceptance of a vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) will be the next major step in fighting the coronavirus disease 2019 (COVID-19) pandemic, but achieving high uptake will be a challenge and may be impeded by online misinformation. To inform successful vaccination campaigns, we conducted a randomized controlled trial in the UK and the USA to quantify how exposure to online misinformation around COVID-19 vaccines affects intent to vaccinate to protect oneself or others. Here we show that in both countries—as of September 2020—fewer people would ‘definitely’ take a vaccine than is likely required for herd immunity, and that, relative to factual information, recent misinformation induced a decline in intent of 6.2 percentage points (95th percentile interval 3.9 to 8.5) in the UK and 6.4 percentage points (95th percen- tile interval 4.0 to 8.8) in the USA among those who stated that they would definitely accept a vaccine. We also find that some sociodemographic groups are differentially impacted by exposure to misinformation. Finally, we show that scientific-sounding misinformation is more strongly associated with declines in vaccination intent. he spread of SARS-CoV-2, the causative agent of COVID-19, have negative consequences for community (herd) immunity, as has resulted in an unprecedented global public health and eco- clustering of non-vaccinators can disproportionately increase the nomic crisis1,2. The outbreak was declared a pandemic by the needed percentage of vaccination coverage to achieve herd immu- T 3 World Health Organization on 11 March 2020 , and development of nity in adjacent geographical regions and encourage epidemic COVID-19 vaccines has been a major undertaking in fighting the spread24. Estimates of acceptance of a COVID-19 vaccine in June disease. As of December 2020, many candidate vaccines have been 2020 suggest that 38% of the public surveyed in the UK and 34.2% shown to be safe and effective at generating an immune response4–6, of the public in the USA would accept a COVID-19 vaccine (a fur- with interim analysis of phase III trials suggesting efficacies as high ther 31% and 25% were, respectively, unsure that they would accept as 95%7–9. At least two vaccine candidates have been authorized for vaccination against COVID-19)25. Worryingly, more recent polling emergency use in the USA10,11, the UK12,13, the European Union14 in the USA (September 2020) has shown significant falls in will- and elsewhere, with more candidates expected to follow soon. For ingness to accept a COVID-19 among both males and females, these COVID-19 vaccines to be successful, they need to be not only all age groups, all ethnicities and all major political groups26, pos- be proven safe and efficacious, but also widely accepted. sibly due to the heavy politicization of COVID-19 vaccination in It is estimated that a novel COVID-19 vaccine will need to be the run up to the 2020 presidential election on both sides of the accepted by at least 55% of the population to provide herd immu- political debate27,28. The public’s willingness to accept a vaccine is nity, with estimates reaching as high as 85% depending on country therefore not static; it is highly responsive to current information and infection rate15,16. Reaching these required vaccination levels and sentiment around a COVID-19 vaccine, as well as the state of should not be assumed given well-documented evidence of vac- the epidemic and perceived risk of contracting the disease. Under cine hesitancy across the world17, which is often fuelled by online these current plausible COVID-19 vaccine acceptance rates, pos- and offline misinformation surrounding the importance, safety sible levels of existing protective immunity—though it is unclear or effectiveness of vaccines18–20. There has been widely circulating whether post-infection immunity confers long-term immunity29— false information about the pandemic on social media platforms, and the rapidly evolving nature of misinformation surrounding the such as that 5G mobile networks are linked with the virus, that vac- pandemic23,30, it is unclear whether vaccination will reach the levels cine trial participants have died after taking a candidate COVID-19 required for herd immunity. vaccine, and that the pandemic is a conspiracy or a bioweapon21–23. Recent studies have examined the effect of COVID-19 misinfor- Such information can build on pre-existing fears, seeding doubt and mation on public perceptions of the pandemic22,31,32, the tendency cynicism over new vaccines, and threatens to limit public uptake of of certain sociopolitical groups to believe misinformation33,34 and COVID-19 vaccines. compliance with public health guidance, including willingness While large-scale vaccine rejection threatens herd immunity to accept a COVID-19 vaccine35,36. However, to our knowledge, goals, large-scale acceptance with local vaccine rejection can also there is no quantitative causal assessment of how exposure to 1Department of Mathematics, Imperial College London, London, UK. 2The Vaccine Confidence Project, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK. 3Department of Health Metrics and Evaluation, University of Washington, Seattle, WA, USA. 4Centre for the Evaluation of Vaccination, Vaccine and Infectious Disease Institute, University of Antwerp, Antwerp, Belgium. 5These authors contributed equally: Sahil Loomba, Alexandre de Figueiredo. ✉e-mail: [email protected]; [email protected] NATURE HUMAN BEhaviouR | VOL 5 | MARCH 2021 | 337–348 | www.nature.com/nathumbehav 337 ARTICLES NATURE HUMAN BEHAVIOUR misinformation affects intent to receive the vaccine and its implica- virus (COVID-19) vaccine became available, would you accept the tions for obtaining herd or community immunity if countries adopt vaccine for yourself?’ (SELF) and ‘If a new coronavirus (COVID- this vaccination strategy. Moreover, it is essential to understand how 19) vaccine became available, would you accept the vaccine if it misinformation differentially impacts sociodemographic groups meant protecting friends, family, or at-risk groups?’ (OTHERS). and whether groups at high risk of developing severe complications Responses were on a four-point scale: ‘yes, definitely’, ‘unsure, but from COVID-19 are more vulnerable to misinformation. leaning towards yes’, ‘unsure, but leaning towards no’ and ‘no, defi- To fill this gap, we developed a pre–post-exposure study design nitely not’. This scale was chosen to remove subjective ambiguity and questionnaire to measure the causal impact of exposure to involved with Likert scales and to allow respondents to explicitly online pieces of misinformation relating to COVID-19 and vac- detail their intent, thereby allowing a more meaningful interpreta- cines on the intent to accept a COVID-19 vaccine, relative to fac- tion of results. tual information. In addition to assessing how misinformation All information (misinformation and factual) was identified might induce changes in vaccination intent, a further aim of this using Meltwater via a Boolean search string eliciting informa- study is to investigate how exposure to misinformation differen- tion and misinformation around a COVID-19 vaccine (Methods, tially impacts individuals according to their sociodemographic ‘Selection of images’). A systematic selection approach was used to characteristics (age, gender, highest education level, employment identify the COVID-19 vaccine information on social media with type, religious affiliation, ethnicity, income level and political affili- high circulation and engagement between 1 June and 30 August ation), daily time spent on social media platforms37, and sources of 2020. Information was classified as misinformation or factual trusted information on COVID-19. Understanding how misinfor- after consulting reputable online sources of knowledge, such as mation differentially impacts sociodemographic groups and indi- peer-reviewed scientific research, webpages of public health orga- viduals according to their social media use or sources of trusted nizations and fact-checking websites (or media outlets employing information can motivate the design of group-specific interventions fact checkers) to verify the content and the context in which it was to reduce the potential impact of online vaccine misinformation. presented (Methods ‘Selection of images’). A final set of five pieces Finally, we assess what makes certain information content more of misinformation comprising non-overlapping messaging and or less likely to influence intent to accept COVID-19 vaccination, themes was selected to represent the diverse messaging found in which can be used to increase effectiveness of public health com- COVID-19 vaccine misinformation (such as information question- munication strategies. ing the importance or safety of a vaccine; Supplementary Table 1). For both the UK and the USA, both the treatment and control As misinformation can be highly country- and context-dependent, groups were nationally representative samples by gender, age and it was decided to expose UK and US respondents to different sets sub-national region. The causal impact of misinformation on vac- of misinformation