Silver linings were few and far between in 2020, but the rapid development of multiple COVID-19 vaccines this past year has given us reason for optimism in 2021. Three of the leading vaccine candidates—those from Pfizer and BioNTech, Moderna, and Oxford and AstraZeneca—demonstrated remarkably high efficacy in Phase III clinical trials, preventing 70 percent to 95 percent of infections, and have been granted emergency authorization by the U.S. Food and Drug Administration.
Critically, we now have a reliable way to stem the pandemic (or at least one that doesn’t rely on facial coverings and social distancing). But whether the vaccines live up to their promise will depend on whether people decide to get vaccinated. And there is reason to worry that Americans will resist.
When deciding whether to get vaccines in general, Americans are highly concerned about side effects. Indeed, this concern is one of the most common reasons people report for delaying or refusing vaccination. Even minor side effects, such as swelling and pain at injection sites, often deter people from vaccination. This is especially true of parents, who are loath to inflict pain on their children. For the COVID-19 vaccine in particular, fear of side effects is, according to a poll in September 2020, the most common reported reason for potential refusal.
Regrettably, evidence suggests that the top COVID-19 vaccine candidates are accompanied by high rates of side effects. For example, in the Pfizer/BioNTech Phase I trial, participants reported markedly high rates of side effects after their second vaccine dose, including fatigue (75 percent), headache (67 percent), chills (33 percent), muscle pain (25 percent), fever (17 percent), and joint pain (17 percent). Early data from Pfizer’s Phase III trial showed lower—but still significant—side effect rates of up to 38 percent.
Vaccines protect us from infection by stimulating the creation of antibodies to a specific germ. Side effects like fever, chills, fatigue, and muscle pain are a sign of reactogenicity—that is, a physical manifestation of a successful immune response.
The high incidence of these COVID-19 vaccine side effects is, from a medical standpoint, not a cause for concern. Actually, side effects often signal that the vaccines are working. Vaccines protect us from infection by stimulating the creation of antibodies to a specific germ. Side effects like fever, chills, fatigue, and muscle pain are a sign of reactogenicity—that is, a physical manifestation of a successful immune response.
From a practical standpoint, the unpleasantness of transient and innocuous side effects is dwarfed by the benefits of preventing infection, especially for a disease as serious as COVID-19. Why, then, might these side effects wield such undue influence over our decisions to get the COVID-19 vaccine? Behavioral science can point us towards several reasons.
First, in light of the uncertainty surrounding the outcomes of COVID-19 (not everyone who gets it suffers—a substantial proportion of those infected, 40 percent, experience mild or no symptoms), individuals may exhibit optimism bias, a tendency to adopt an overly optimistic view about oneself and one’s likelihood of experiencing negative events. Indeed, many Americans grossly underestimate their susceptibility to infection and their body’s ability to fight the virus. When faced with the decision of whether or not to get the COVID-19 vaccine, individuals could feel the near-certainty of unpleasant side effects outweighs the possibility of preventing COVID-19.
Second, in the absence of a clear understanding of reactogenicity, people could mistakenly believe that these side effects are a sign that the vaccines are unsafe. A majority of Americans are already concerned that the COVID-19 vaccine approval process is moving too fast without fully establishing safety and effectiveness. (In truth, the vaccines are based on decades of research that affirms the safety of the mRNA-style vaccines, and the approval process upheld the high standards required by the field of medicine.) Moreover, side effects that mimic the symptoms of COVID-19 (fatigue, chills, fever, muscle and joint pain) could bolster the pervasive belief that vaccines can cause, rather than prevent, disease. The strengthening of these false beliefs could be exacerbated by the human tendency to pay attention to evidence in support of—and disregard evidence in conflict with—their prior beliefs, a phenomenon known as confirmation bias.
While common side effects of the COVID-19 vaccine may not pose a direct threat to public health, when examined through the lens of behavioral science, they could have drastic consequences on vaccine acceptance.
Thus, while common side effects of the COVID-19 vaccine may not pose a direct threat to public health, when examined through the lens of behavioral science, they could have drastic consequences on vaccine acceptance. How, then, should we promote uptake of a COVID-19 vaccine that has frequent and unpleasant side effects? There are several evidence-based approaches that health practitioners, scientists, and informed members of the general public can take to encourage vaccine acceptance among those concerned about vaccine side effects.
Explain that side effects are a positive sign that the vaccine is working as anticipated.
Informing patients about reactogenicity could help people to view side effects as an encouraging signal that their body is getting prepared to fight off infection. Side effects could then be considered a form of positive feedback which reduces uncertainty over whether vaccine is actually working. Linking the discomfort of side effects to a prosocial outcome (e.g., reducing the risk that you could transmit COVID-19 to more vulnerable populations) could also trigger the “martyrdom effect,” where the prospect of suffering for the prosocial cause can ascribe greater meaning to prosocial contributions, increasing willingness to contribute.
Make your explanation of reactogenicity straightforward and compelling.
People are more likely to perceive information as true if it is easy to understand and aligns with existing beliefs or values. Thus, providing an uncomplicated explanation of reactogenicity which reflects an individual’s values (e.g. to make one’s body stronger and more resilient, to protect one’s family and friends, etc.) could increase the likelihood that one could adopt this explanation. Importantly, making the explanation of reactogenicity more cognitively “digestible” could also make it easier to adopt and recall in the face of dangerous vaccine myths.
Avoid direct attempts to ‘debunk’ vaccine myths.
Efforts to debunk myths can backfire. For instance, in a 2015 study assessing the effects of messaging countering the myth that the flu vaccine causes the flu, researchers found that, while the corrective information reduced belief in the myth, it also significantly reduced intent to vaccinate among those highly concerned about side effects. Why? Merely hearing a piece of misinformation, even within a statement attempting to dispel it, could increase people’s familiarity with the myth and cause them to recall it as if it were true. Instead of redressing these myths, focus instead on the real reason for side effects: reactogenicity—the physical signs of a successful immune response.
In the coming year, increasing COVID-19 vaccine acceptance will be crucial. With rapidly rising case rates and failed efforts to reduce risky behaviors amid pandemic fatigue, a COVID-19 vaccine may be our only lifeboat out of the pandemic, but only if a substantial proportion of people choose to get the vaccine. Behavioral science provides key insights into how frequent vaccine side effects could sink this lifeboat. It also points to ways we might be able to keep it afloat.