Impact of risk communication format on risks related to COVID-19 vaccines

In a recently published study in healthcarethe researchers examined the association between risk communication format and perceived vaccine-related risks of the 2019 coronavirus disease (COVID-19).

Study: Association between risk communication format and perceived risk of adverse events after COVID-19 vaccination in US adults. Image Credit: CKA/Shutterstock

Vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a crucial strategy to prevent severe COVID-19. However, fear of vaccine-related adverse events and side effects may affect vaccine uptake. Studies have recently shown that adults fear vaccine-related side effects. These risks are currently described in verbal terms; While well intentioned, this could be problematic as the format of risk communication can influence risk perception and decision making.

About the study

The present study examined how the format of risk communication affects risk perceptions related to COVID-19 vaccines. They conducted an online survey among adult individuals recruited through a crowdsourcing platform, Mechanical Turk (MTurk), in the United States (USA) in January 2022. Eligible subjects were between 18 and 90 years old and had an MTurk rating of over 98%.

Subjects who had not received all primary and booster immunizations were randomized to receive information on three adverse events (fatigue, fever, and headache) and one adverse event (myocarditis) after COVID-19 vaccination, using numerical risk estimates or verbal descriptors were used. Myocarditis was described as an infrequent event (verbal) or 0.001205% (numerical), while fever, fatigue and headache were described as common or 8%, 47% and 41%, respectively.

Participants rated their perceived risk of developing side effects after their given vaccine dose on a scale of 100%. The survey was designed to also collect demographic and political identity information. Participants’ intent to take the next vaccine dose was assessed and they were stratified based on responses as vaccine acceptance, refusal, delay, or hesitation.

Participants reported on the impact of different sources of information on COVID-19 vaccines, such as B. Social media, healthcare professionals, family members, news media, religious, school or professional communities and public health organizations. A linear regression model examined the influence of verbal and numerical descriptors on perceived risks.


A total of 939 people took part in the online survey. Of these, 575, 61 and 303 were fully, partially and unvaccinated, respectively. The mean age of the participants was 39 and 55.6% were men. There were 444 participants randomized to verbal descriptors and 495 to numeric descriptors. Participant characteristics were balanced between the groups.

The mean risk perception was more variable and higher in the verbal descriptor arm for the common side effects. The largest difference (between groups) was for fever with an estimated risk of 41.4% in the verbal descriptor arm versus 15.4% in the numeric descriptor arm. For fatigue and headaches, the differences between the groups were smaller.

The standard deviations were much larger for each side effect in the verbal descriptor arm, suggesting greater variability in risk perception with verbal risk descriptors. A multivariable analysis found that verbal descriptors were associated with a higher perceived risk of vaccine-related adverse events. Increased social media influence or political identity were not associated with differences in perceived risks.

Individuals who refused and postponed the vaccine had a higher perceived risk of fatigue and headaches than those who accepted the vaccine. People who were hesitant to vaccinate showed no increased risk perception. Participants exposed to the verbal descriptor (rarely) had a higher perceived risk of myocarditis than those in the numerical descriptor arm. Multivariable analyzes showed an association between verbal descriptors and a higher perceived risk of myocarditis.

Individuals who were influenced by social media also had an increased risk perception for myocarditis. A lower perceived risk of myocarditis was observed among those with a more liberal political identity. Vaccination hesitant and procrastinators had a lower perceived risk of myocarditis than those who accepted the vaccine. Male gender was associated with a lower perceived risk of side effects and myocarditis.


Results of the online survey showed that verbal descriptors resulted in a more variable, less accurate, and higher perceived risk of adverse events associated with COVID-19 vaccines than numeric descriptors. The results underscore the potential value of moving from verbal descriptors to numerical risk estimates. Respondents in the verbal descriptor arm consistently reported risks of between 40% and 50% for vaccine-related adverse events.

However, there were minor differences between the estimated risk perceptions and the published risk estimates. The median perceived myocarditis risk was more than 1000-fold higher for verbal descriptors than for numerical estimates. Taken together, verbal descriptions of risks associated with COVID-19 vaccines may increase risk perceptions in adults. Individuals who are heavily influenced by social media may have heightened risk perceptions, regardless of the communication format.

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