Numbers can be powerful. Many of us can’t resist the urge to buy a lottery ticket when we hear that the jackpot is more than half a billion dollars (even though our chance of winning is miniscule). We count down the number of days before our next vacation, the end of school, or some other important life moment. And we decide whether to make a purchase based, at least in part, on the numbers related to an item (e.g., cost, size, quantity, etc.). But how often do you use numbers when speaking to your patients? Generally, we are told to avoid numbers when talking with patients and families:

“Too many numbers are overwhelming.”

“People don’t understand numbers.”

“Science and math are boring. You need to appeal to a person’s emotion.”

Indeed, each of these statements can be true in certain situations or with some individuals or audiences, but does that mean we should avoid the use of numbers altogether?

Numeric vs. verbal side effects descriptions

A recent study published in Vaccine by Shoots-Reinhard and colleagues suggests that we should consider the use of numbers, at least when talking about vaccine side effects (Shoots-Reinhard B, Lawrence ER, Schulkin J, Peters E. “Excluding numeric side-effect information produces lower vaccine intentions.” Vaccine. 2022 Jul 29; 40(31):4262-4269). In an online survey of about 600 people, Shoots-Reinhard and colleagues described the side effects of a hypothetical vaccine in four ways: verbal-only descriptions (very rare, uncommon, common, very common), numeric-only descriptions (presented as percentages), both verbal and numeric descriptions, or no frequency-related information (list of side effects only).

The authors found that “providing numeric information about vaccine side effects increased likelihoods of getting vaccinated compared to not providing it” (p. 4266), and provision of both types of information had the greatest effect on intent to receive the vaccine among hesitant individuals. Likewise, offering both verbal and numeric descriptions increased perceptions of side effects as being of a less serious nature, including reducing concerns about rare but severe side effects.

To evaluate side effect frequency estimations, participants were also asked to recall the likelihood of three side effects of varying frequency. Those who were exposed to numeric information were less likely to overestimate frequencies compared with those who did not have exposure to numeric data. In considering the role of numbers, the authors suggested that “The benefits of numeric information appear due to them playing an overlooked educational role, correcting the near ubiquitous overestimation of the likelihood of side effects” (p. 4267).

While this study had limitations and needs to be expanded, it provides an important context for consideration. Indeed, one effective anti-vaccine strategy involves touting the number of reports about a particular condition submitted to the Vaccine Adverse Events Reporting System (VAERS) as proof that vaccines are the cause. Of course, this is maddening to those who understand that VAERS data do not offer a controlled study, and therefore cannot demonstrate a causal relationship between a possible side effect and vaccination. However, this fact does not stop people from being frightened by the numbers.

Transparent vs. vague messaging

Interestingly, Petersen and colleagues looked at transparent versus vague messaging related to COVID-19 vaccine acceptance, and while at first glance their findings may seem at odds with those of Shoot-Reinhard, on closer examination they are not so different.

Petersen and colleagues completed two surveys, one prior to and one after release of COVID-19 vaccines (Petersen MB, Bor A, Jorgensen F, Lindholt MF. “Transparent communication about negative features of COVID-19 vaccines decreases acceptance but increases trust.” Proc Natl Acad Sci U S A. 2021 July 20;118(29):e2024597118.) The authors evaluated transparent messaging that was positive, negative or neutral (e.g., side effects better, worse or similar to those caused by influenza vaccine, respectively). In the second study, they also compared this messaging with vague messaging (e.g., “acceptable side effect” rates). Subjects were evaluated for their individual tendencies toward vaccine skepticism, based on their positions related to uncertainty, conspiratorial thinking, threats afforded by the COVID-19 pandemic (real and symbolic), and political ideology.

While the studies indicated that transparent negative communication increased skepticism in the short term, particularly among those who distrust authorities, they found that transparent positive and neutral communication increased vaccine support. Further, when the authors compared transparent communication to vague communication, they found that, like transparent negative communication, vague communication also decreased vaccine support; however, it also increased endorsement of conspiracy beliefs, whereas transparent negative communication did not influence conspiracy beliefs. Additionally, vague communication eroded trust in health authorities.

In concluding, the authors stated (p. 7of 8):

Overall, these results underscore that transparency itself cannot reduce immediate vaccine skepticism but transparency is nonetheless of key importance for sustaining long-term trust and avoiding the spread of conspiracy beliefs. Furthermore, while there are clear short-term costs to transparent negative communication, there are no benefits to the alternative of reassuring the public about vaccine safety and effectiveness using vague communication, which leads to both short-term vaccine skepticism and long-term distrust of authorities.


In sum, these studies suggest that we pay a price for being vague, and while we don’t want to overwhelm families with “the numbers,” opportunities exist to provide more specific information, and when we do, we may not only increase their vaccine acceptance but also their trust in us.

Did you know?

The VEC’s free mobile app, Vaccines on the Go, offers side effect rates with verbal and numerical descriptions for routinely recommended and travel vaccines across the lifespan. It is available for Apple and Android phones. Bonus: You can send us your questions through the app!

Materials in this section are updated as new information and vaccines become available. The Vaccine Education Center staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family's personal health. You should not use it to replace any relationship with a physician or other qualified healthcare professional. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult your physician or, in serious cases, seek immediate assistance from emergency personnel.