It is vitally important – to the informed consent process, public trust and public health policy – to study, understand and transparently explain vaccine adverse events. And, despite what you may have heard from anti-vaccine advocates like RFK Jr., this is happening. Indeed, few, in any, biomedical interventions are as thoroughly studied and systematically monitored as vaccines.
Despite this reality, there has been a rise in attention and concern about vaccine safety. This has contributed to a deadly increase in vaccine hesitancy and has been largely driven by misinformation from social media influencers, podcasters, anti-vaccine organizations and, perhaps most worrisome, politicians. Indeed, in both Canada and the U.S., the topic of vaccine safety has become highly partisan. It has emerged as a major talking point in political circles with some legislators going so far as to seek the banning of certain vaccine technologies, and even the discussion and promotion of COVID vaccines by public health officials.
But even with all this public discourse and politicizing about vaccine safety, an important factor relevant to this topic is rarely noted: all this noise may be contributing to the perception that adverse events are occurring. Indeed, we seem to be in the middle of an accelerating vaccine concern vortex. The more we talk about vaccine safety, the more people believe it is an issue, the more people are likely to believe they have experienced a vaccine safety event which, in turn, leads to yet more discussion and more concern.
A growing body of evidence has connected perceived adverse reactions to vaccines to nonpharmaceutical (that is, psychological) causes (i.e., a nocebo effect, which occurs when someone expects a negative outcome from a treatment or situation, triggering worse health.) For example, a 2022 systematic review and meta-analysis of the adverse events reported in the placebo arm of COVID vaccine trials found that nocebo responses accounted for remarkable 76 per cent of the systemic adverse events (such as headache or fatigue, as opposed to a local issue, like a sore arm). And, as highlighted in a 2024 study, a positive view of vaccines can lead to a better vaccine experience. Specifically, the researchers concluded “people with a more positive vaccine mindset reported fewer side effects, less same-day vaccine-related anxiety, and improved affective outcomes after vaccination.”
In addition, prior hesitancy and concern about the COVID vaccine has been shown, again in numerous studies, to be associated with adverse reactions. For example, a 2024 Danish study of more than 85,000 found that “participants with specific COVID-19 vaccine concern had higher odds of reporting one or more systemic AEs following vaccination compared with those who had no specific COVID-19 vaccine concern.” A 2024 German study on COVID vaccination experiences concluded that “expectations of low benefit and high adverse effects” were associated with vaccination adverse events. And a 2022 study showed that “a quantifiable and meaningful portion of COVID-19 vaccine side-effects is predicted by vaccine hesitancy.”
How health interventions are represented in the popular press, and in pop culture more broadly (e.g., on popular podcasts and social media) plays an important role in this context. Numerous studies have shown that media coverage can impact how individuals react to biomedical intervention. A 2022 study, for example, found that positive media attention of cannabis-based therapies “may shape placebo responses” as a pain therapy. In other words, widespread media coverage suggesting that cannabis helps with pain increased the perception, via the placebo effect, that cannabis helped with pain.
Other research has found that media coverage can also increase the nocebo response. A 2019 study looked at adverse events reporting before and after media coverage of an antidepressant controversy and found that “media reports of side effects appear to cause a strong nocebo response by increasing both the overall rate of side effect reporting and an increase in the specific side effects mentioned in the media coverage.” And, no surprise, research has also concluded that media coverage of the COVID vaccine side effects resulted in a “media-induced nocebo response” due to “elevated symptom experience from anxiety, and consequently greater reporting of the symptoms in line with the media coverage.”
Thus, the media we consume can play a role in our vaccine behaviour and perceptions. It also seems likely to amplify pre-exiting beliefs. Those who are most concerned about vaccine safety and are vaccine hesitant are more likely to get their news and information from social media, low-quality online sources and from media outlets that often push vaccine misinformation.
And this leads us to a particularly interesting and challenging association: political identity is linked to the reporting of adverse events. A 2024 study of over 600,000 COVID vaccine adverse events found that the more a jurisdiction voted Republican, “the more likely their vaccine recipients or their clinicians are to report COVID-19 vaccine AEs.” While this may seem surprising, it makes sense. As vaccines become more and more about politics, particular political communities will hear messaging that aligns with their position on vaccines. Numerous studies have found that those who identify with the political right are more likely to have less confidence in the COVID vaccines and less likely to think they have benefit.
There are many psychological forces that likely contribute to the sway of vaccine rhetoric, including, inter alia, the illusory truth effect (the more we hear about something, even if it is false, the more likely we are to believe it), the negativity bias (we remember and respond to the scary and rage inducing stuff) and the power of anecdotes (one scary story can overwhelm a large body of evidence on safety and efficacy). Also, widely circulated concerns about vaccine safety may heighten the impact of the illusion of causality – that is, mistakenly believing one event (getting a vaccine) caused a particular outcome (an adverse health event).
All these psychological, political and echo-chamber enhanced tendencies will make it difficult to counter the harms done by the vaccine safety concern vortex. Indeed, worry about safety and adverse events seems likely to have not only played into the agenda of more extreme anti-vaccine individuals, but may have also influenced perceptions more broadly – such as in the context of the low uptake of COVID boosters and the preference to get the flu and COVID vaccines separately, despite the fact that simultaneous administration has been found to be safe, efficient and not associated with increased adverse events.
To repeat, studying vaccine adverse events is critically important. As with all health interventions, there are risks associated with vaccines. Understanding more about them will make vaccines even safer and help to build trust and confidence. And while serious adverse events are rare, they do occur. We need to respectfully listen to and not minimize the experiences of those who feel they’ve had an adverse event. Indeed, from the perspective of the patient, both the placebo and nocebo effect are very real. How people experience vaccination should not be dismissed or mocked.
But it is also important to understand the complex forces that shape how individuals and communities perceive and react to vaccines and rhetoric about vaccine safety. How we talk about vaccines matters. It impacts public health policy, public perceptions, adverse event reporting and vaccination experiences.
Given the dominant role the nocebo effect seems to play in this context, we need to build on the existing research on communication strategies – such as fostering more positive expectations – that may counter its effect. We must also vigorously counter the misinformation and political spin that helps to fuel the accelerating vaccine concern vortex.
