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MARCH 2021 | VOL. 22 NO. 1 | ISSN 1479-2699
Assuring the safety
of vaccines
The plastisphere
Mandatory childhood vaccination
Latin anyone?
A psychological ‘vaccine’
against fake news
misinformation—especially on social media—outpaces
the rate at which we can fact-check and so people are
repeatedly fooled by manipulative information. In other
words, debunking is never agile enough: even if it works,
the damage is often already done, and the myth continues
to spread.
This leads to the natural question of whether we can
prevent misinformation from taking root in the first place?
In the 1960s, American psychologist William McGuire
developed a framework known as inoculation theory,
which closely follows the biomedical analogy. In brief,
McGuire posited that—similar to a biomedical vaccine—the
‘cognitive immune system’ needs to become familiar with
a weakened version of the ‘virus’ (the manipulation
attempt) in order for it to develop ‘mental antibodies’.
At the time, McGuire was thinking about people’s
susceptibility to propaganda during the Cold War and
whether it was possible to produce a ‘vaccine against
brainwash’. Although he had some initial success with
his experiments, showing that people can become more
immune to persuasion when they are forewarned and
exposed to a severely weakened version of the ‘persuasive
attack’, he never quite tested his ideas in the context of
propaganda, and the theory slowly faded into history.
Sixty years later, at the Cambridge Social Decision-Making
Lab, we decided to renew focus on inoculation theory. One
insight that McGuire may not have foreseen is that we can
As governments across the world are rolling out COVID-19
vaccination policies, they are not only facing challenges
around vaccine logistics but are also fighting an uphill
battle against the onslaught of ‘fake news’. In fact,
commentators have argued that misinformation might
be the most contagious thing about the virus. The
consequences of belief in fake news can be dangerous,
whether it concerns fake cures that lead people to ingest
harmful substances or vandalisation of the 5G network
infrastructure because of false assertions that there is a
link between radiation and COVID-19. In our recent
research, we found clear evidence that belief in common
misinformation about the virus is strongly associated with
reduced intentions to get vaccinated and a lower likelihood
to recommend the vaccine to others. We therefore need an
effective way to counteract and tackle the spread of
misinformation in society.
Despite years of research in cognitive and behavioural
science on how to curb the impact of misinformation, a
magic bullet solution for the problem has not been found.
The classical method is known as debunking and entails
issuing a correction after people have already been
exposed to a falsehood. This method leaves much to be
desired because it often requires repeating the myth in an
effort to debunk it. We know that the more someone is
exposed to a myth, the more familiar the myth feels, and
the more weight the brain will give the claim in memory
retrieval: an effect known as the illusory truth effect. In
other words, when fact-checking misinformation, there is
always a risk that the myth becomes more readily available
in one’s memory, potentially leading to a negative effect
that reinforces the myth while people easily forget about
the correction. Sometimes the benefits of debunking
outweigh the adverse effects of potentially increasing
familiarity through repetition but even when debunking is
effective, it does not solve the problem: the spread of
Rakoen Maertens and Sander van der Linden
University of Cambridge, UK
microbiologist | March 2021
now actually borrow models from epidemiology to study
the spread of information pathogens. Misinformation is
highly contagious as it can spread from one person to
another without the need for physical contact. The vaccine
analogy has, therefore, never been more apt.
To develop a scalable vaccine that provides long-term
cognitive protection against a wide range of
misinformation pathogens, we further developed the
prophylactic framework of inoculation theory—otherwise
known as ‘prebunking’. To illustrate how this approach
works in a controlled laboratory environment, we started
by evaluating whether we could distil a sufficiently
weakened dose out of a specific myth: misinformation
about climate change. In particular, we used a screenshot
of a real website that hosts a bogus petition allegedly
signed by thousands of scientists claiming that global
warming is a hoax. In the experiment, we forewarned
people about the petition (without naming it) and
provided them with a pre-emptive refutation (a weakened
dose that contains the ‘prebunk’). For example, the
forewarning message contained an explanation of the
flaws and fallacies utilised in the misinformation (e.g. the
use of fake experts, including false signatories such as microbiologist | March 2021 15
Charles Darwin and members of the Spice Girls). The
warning and weakened dose are meant to trigger people’s
vigilance and attention (to start the production of mental
antibodies), and the message offers people concrete
ways to resist the misinformation. After people were
inoculated, participants were exposed to a full dose of the
misinformation. Our findings showed that while those who
received a placebo treatment were negatively impacted
by the misinformation, inoculated participants were
substantially less likely to be fooled by it. This experiment
was replicated three times and extended to show that even
one week after the intervention, inoculated individuals
were still protected against the misinformation attack.
After some initial success with an isolated issue in one
context, we successfully developed the first vaccine of the
second generation: an intervention to inoculate people
against a broad range of misinformation tactics. Rather
than trying to pre-empt every single myth, we deemed it
more efficient to develop a broader-spectrum vaccination
that targets the very building blocks of the misinformation
virus itself (its nucleic acid). After a year’s worth of
investigation, we identified the techniques common to
nearly all online misinformation; ‘The Six Degrees of
Manipulation’: discrediting, appealing to emotion, group
polarisation, impersonation (e.g. fake experts), conspiracy
theories and trolling. An important second theoretical
innovation was that we wanted to simulate a social media
feed to increase the validity of our testing environment.
This also allowed us to examine the notion of ‘active
inoculation’ or the idea that instead of passively
providing people with the facts beforehand, you let
people generate their own intellectual antibodies in an
interactive learning setting.
Accordingly, in collaboration with the Dutch media literacy
organisation DROG, we designed the inoculation-based
game Bad News ( In the game,
participants take on the role of misinformation producer
and aim to gain followers (whilst maintaining their
credibility) by creating and sharing manipulative news
headlines according to one of the six degrees of
manipulation. During gameplay, players are forewarned
about the dangers of fake news and are exposed to
weakened doses of the six manipulation techniques in a
controlled environment, often using humour. Importantly,
these doses are strong enough to trigger people’s
motivation to learn how to protect themselves but not so
strong as to actually dupe them (or infect people with the
virus). Players typically participate in a quiz beforehand
where they are asked to rate how reliable they find a large
series of posts that are either credible news items or items
that contain one of the key misinformation techniques.
Notably, the test items are different from the training items
used in the game. Both big data samples (of people who
voluntarily play the game) as well as randomised controlled
trials on the Bad News game have shown that it effectively
reduces people’s susceptibility to fake news headlines, that
the game boosts people’s confidence in their own ability to
discern manipulative from credible news and reduces
self-reported readiness to share fake news.
After these promising findings, we decided to further test
and evaluate our intervention with the UK government.
The government helped translate the game into 20
languages around the world, which enabled us to do
additional large-scale cross-cultural replications with
positive results. The game has now been played by over
a million people around the world and is implemented in
high school and university curricula in several countries.
Following the recent declaration by the World Health
Organization (WHO) of a worldwide ‘infodemic’ and the
success of our second-generation vaccine, we set out to
develop a similar inoculation game to help protect people
against the harmful impact of COVID-19 misinformation
specifically. Together with the UK Cabinet Office and with
support from the WHO and United Nation’s Verified
Graffiti on a Manchester
motorway bridge about
COVID-19 being a hoax
microbiologist | March 2021
campaign, we launched GoViral! The GoViral! Game
prebunks three common techniques used to spread
misinformation about the coronavirus: fearmongering,
the use of fake experts and conspiracy theories.
Although these advances are promising, we needed to
know more about the long-term efficacy of the cognitive
vaccine. Similar to how it is imperative to determine the
long-term effectiveness of COVID-19 vaccines, research on
inoculation-based interventions will need to investigate
how to increase the interventions’ long-term success. In
general, the literature shows that the benefits of cognitive
inoculation remain intact for up to two months, but that
its effectiveness starts to dissipate after a few weeks.
Importantly, research has found evidence for the potential
of ‘booster sessions’. Just like for the Pfizer vaccine—where
a booster jab is needed three weeks after the initial
injection—cognitive immunity can be prolonged with an
additional ‘booster shot’. In an experiment with Bad News,
we found evidence for inoculation effect decay after two
months when we excluded follow-ups, but full retention of
the protective effects for at least three months after three
booster sessions. Ultimately, we aim to follow the vaccination analogy to its
logical conclusion: herd immunity. Psychological vaccines
do not work in exactly the same manner as biological
vaccines of course, their efficacy is nowhere near 95%
immunity and they wear off over time if not boosted
regularly. Having said this, we are currently running
computer simulations to try to estimate what percentage
of a population needs to be vaccinated at a sufficient rate
within a given (online) community to effectively contain
the spread of misinformation. To help ensure that
misinformation-induced vaccine hesitancy does not spread
further, governments, schools, technology companies and
civil society can therefore help spread and scale the vaccine.
For example, some social media companies, such as Twitter,
have already started experimenting with prebunking on
their platform. We are currently collaborating with Google,
who through their research and innovation hub Jigsaw, is
helping us to develop short inoculation videos, which could
be embedded as an advertisement on, for example,
YouTube (before people are exposed to misinformation).
However, at the end of the day, we need a multi-layered
defence system. We need to prebunk first where possible,
but also continue to rely on real-time fact-checking as well
as debunking after the fact if needed. Only if these
combined pre- and debunking measures are implemented
quickly, widely and in various settings, will we be able to
contain the spread of misinformation in society.
At present, we do not yet know at what rate the
misinformation virus evolves, but we know it is getting
more sophisticated. As with any virus, we have to stay alert
and be ready to update our vaccines whenever a new
variant of misinformation arises. In the words of the
renowned Defence against the Dark Arts Professor, Severus
Snape, ‘our defences must be as flexible and inventive as
the arts we seek to undo’.
Basol M, Roozenbeek J, van der Linden S.
Good news about Bad News: gamified inoculation
boosts confidence and cognitive immunity against fake
news. Journal of Cognition 2020; 3(1), 1–9
Maertens R, Anseel F, van der Linden S. Combatting
climate change misinformation: evidence for longevity of
inoculation and consensus messaging effects. Journal of
Environmental Psychology 2020; 70, 101455
Maertens R, Roozenbeek J, Basol M, van der Linden S.
Long-term effectiveness of inoculation against
misinformation: three longitudinal experiments.
Journal of Experimental Psychology: Applied 2020.
Advance online publication.
Roozenbeek J, Schneider CR, Dryhurst S, Kerr J,
Freeman ALJ, Recchia G et al. Susceptibility to
misinformation about COVID-19 around the world.
Royal Society Open Science 2020; 7(10), 201199.
Roozenbeek J, van der Linden S. Fake news game confers
psychological resistance against online misinformation.
Palgrave Communications 2019; 5(1), 65
van der Linden S, Roozenbeek J, Compton J. Inoculating
against fake news about COVID-19. Frontiers in
Psychology 2020; 11, 566790
Screenshot of GoViral!, a game illustrating the fake expert technique
( microbiologist | March 2021 17
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
The outbreak of the SARS-CoV-2 novel coronavirus (COVID-19) has been accompanied by a large amount of misleading and false information about the virus, especially on social media. In this article, we explore the coronavirus “infodemic” and how behavioral scientists may seek to address this problem. We detail the scope of the problem and discuss the negative influence that COVID-19 misinformation can have on the widespread adoption of health protective behaviors in the population. In response, we explore how insights from the behavioral sciences can be leveraged to manage an effective societal response to curb the spread of misinformation about the virus. In particular, we discuss the theory of psychological inoculation (or prebunking) as an efficient vehicle for conferring large-scale psychological resistance against fake news.
Full-text available
Misinformation about COVID-19 is a major threat to public health. Using five national samples from the UK (n= 1050 and n= 1150), Ireland (n = 700), the USA (n = 700), Spain (n= 700) and Mexico (n= 700), we examine predictors of belief in the most common statements about the virus that contain misinformation. We also investigate the prevalence of belief in COVID-19 misinformation across different countries and the role of belief in such misinformation in predicting relevant health behaviours. We find that while public belief in misinformation about COVID-19 is not particularly common, a substantial proportion views this type of misinformation as highly reliable in each country surveyed. In addition, a small group of participants find common factual information about the virus highly unreliable. We also find that increased susceptibility to misinformation negatively affects people's self-reported compliance with public health guidance about COVID-19, as well as people's willingness to get vaccinated against the virus and to recommend the vaccine to vulnerable friends and family. Across all countries surveyed, we find that higher trust in scientists and having higher numeracy skills were associated with lower susceptibility to coronavirus-related misinformation. Taken together, these results demonstrate a clear link between susceptibility to misinformation and both vaccine hesitancy and a reduced likelihood to comply with health guidance measures, and suggest that interventions which aim to improve critical thinking and trust in science may be a promising avenue for future research.
Full-text available
This study investigates the long-term effectiveness of active psychological inoculation as a means to build resistance against misinformation. Using 3 longitudinal experiments (2 preregistered), we tested the effectiveness of Bad News, a real-world intervention in which participants develop resistance against misinformation through exposure to weakened doses of misinformation techniques. In 3 experiments (N Exp1 ϭ 151, N Exp2 ϭ 194, N Exp3 ϭ 170), participants played either Bad News (inoculation group) or Tetris (gamified control group) and rated the reliability of news headlines that either used a misinfor-mation technique or not. We found that participants rate fake news as significantly less reliable after the intervention. In Experiment 1, we assessed participants at regular intervals to explore the longevity of this effect and found that the inoculation effect remains stable for at least 3 months. In Experiment 2, we sought to replicate these findings without regular testing and found significant decay over a 2-month time period so that the long-term inoculation effect was no longer significant. In Experiment 3, we replicated the inoculation effect and investigated whether long-term effects could be due to item-response mem-orization or the fake-to-real ratio of items presented, but found that this is not the case. We discuss implications for inoculation theory and psychological research on misinformation. Public Significance Statement This study shows that inoculation-based media and information literacy interventions such as the Bad News Game can confer protection against the influence of misinformation over time. With regular assessment, the positive effects can be maintained for at least 3 months. Without regular "boosting," the effects dissipate within 2 months.
Full-text available
Recent research has explored the possibility of building attitudinal resistance against online misinformation through psychological inoculation. The inoculation metaphor relies on a medical analogy: by pre-emptively exposing people to weakened doses of misinformation cognitive immunity can be conferred. A recent example is the Bad News game, an online fake news game in which players learn about six common misinformation techniques. We present a replication and extension into the effectiveness of Bad News as an anti-misinformation intervention. We address three shortcomings identified in the original study: the lack of a control group, the relatively low number of test items, and the absence of attitudinal certainty measurements. Using a 2 (treatment vs. control) × 2 (pre vs. post) mixed design (N = 196) we measure participants' ability to spot misinformation techniques in 18 fake headlines before and after playing Bad News. We find that playing Bad News significantly improves people's ability to spot misinformation techniques compared to a gamified control group, and crucially, also increases people's level of confidence in their own judgments. Importantly, this confidence boost only occurred for those who updated their reliability assessments in the correct direction. This study offers further evidence for the effectiveness of psychological inoculation against not only specific instances of fake news, but the very strategies used in its production. Implications are discussed for inoculation theory and cognitive science research on fake news.
Full-text available
The spread of online misinformation poses serious challenges to societies worldwide. In a novel attempt to address this issue, we designed a psychological intervention in the form of an online browser game. In the game, players take on the role of a fake news producer and learn to master six documented techniques commonly used in the production of misinformation: polarisation, invoking emotions, spreading conspiracy theories, trolling people online, deflecting blame, and impersonating fake accounts. The game draws on an inoculation metaphor, where preemptively exposing, warning, and familiarising people with the strategies used in the production of fake news helps confer cognitive immunity when exposed to real misinformation. We conducted a large-scale evaluation of the game with N = 15,000 participants in a pre-post gameplay design. We provide initial evidence that people's ability to spot and resist misinformation improves after gameplay, irrespective of education, age, political ideology, and cognitive style.