Only about 50 percent of Americans are fully vaccinated against the coronavirus — a number that barely changed at all in July. As rates remain stagnant, many of those 50 percent are grappling with the same question the Biden administration is facing: How do we persuade our fellow citizens to get vaccinated?

That question has roiled federal agencies, state universities and the National Football League in just the past week. On Wednesday, Buffalo Bills wide receiver Cole Beasley delivered a statement explaining that he hadn’t gotten vaccinated in part because he feels that “information is being withheld from players” and “we don’t know enough” about the vaccines.

Beasley isn’t alone. According to the Kaiser Family Foundation Vaccine Monitor, two leading reasons people aren’t getting vaccinated are the newness of the vaccine and the possibility of unknown side effects. And nearly half of unvaccinated Americans are more worried about vaccine side effects than about contracting covid-19.

Most public health efforts to persuade the vaccine-reluctant have focused on pointing out covid-19’s known lethality and other dangers — making the case that those outweigh the potential unknowns about the vaccines’ long-term effects.

My research on how anxiety influences politics suggests that this may be a mistake.

Anxiety shapes political behavior in ways fear does not

Psychologically, fear and anxiety are related but crucially distinct concepts. Fear takes an immediate object; anxiety does not. That is, when we worry about shark attacks at the beach, it’s anxiety. When we see a dorsal fin, it’s fear. Anxiety, in essence, is fear plus uncertainty — the “unknown unknown” that can never be fully resolved. And that uncertainty matters — a lot.

Considerable research in neuroscience and psychology has made clear just how much uncertainty destabilizes the human mind. This comes as little surprise to anyone who has waited in limbo for potentially grave news — about a missing loved one, a final-exam grade, the results of a major medical test. Our brains in some ways prefer even bad news over uncertainty. In a 1966 experiment, psychologists found that receiving a very minor electrical shock at unpredictable intervals was much more distressing for participants than receiving a significantly more painful shock that came after a warning bell.

My research shows that the pressure to convert anxiety into fear — to impose order on an uncertain and threatening world — has major implications for U.S. politics and foreign policy. For instance, the U.S. response to some of the unprecedented threats of modern history — such the sudden advent of nuclear competition under President Harry S. Truman, or the 9/11 attacks — was centrally guided by how foreign policy experts dealt with uncertainty-driven anxiety, as I explore in my dissertation.

Uncertainty affects the public, too. In a recent survey experiment, political scientist Christopher Gelpi and I found evidence that public support for the war on terrorism seems to be driven in part by the need to manage anxiety about unrelated threats — including covid-19. When people were reassured about covid-19, they were less likely to be concerned about terrorism in general or to support related policies.

Political psychology reveals just how broadly uncertainty and anxiety can shape politics. For instance, people who struggle to handle uncertainty are much more likely to support baseless ideologies such as QAnon. And people inclined toward those baseless ideas are more likely to underestimate the risk of covid-19 and less likely to follow public health guidance.

Anxiety isn’t all bad. It can sometimes spur us to seek new information — making us less beholden to partisan assumptions and more willing to listen to experts. But there can be a downside. In their 2015 book “Anxious Politics,” political scientists Bethany Albertson and Shana Gadarian point out that anxiety can be readily exploited by political demagogues who “offer bodily protection while destroying the body politic” — especially when public trust in institutions and experts is weak.

Uncertainty is a big part of why people hesitate to get vaccinated

Most arguments in favor of vaccination have sought to leverage fear — the known and very real dangers of contracting covid-19 — against anxiety — the highly unknowable long-term side effects of the vaccines. That makes a certain amount of sense, especially for those who can tolerate uncertainty — such as that around a new vaccine — much better than others.

But for those who are still waiting, it’s probably a different story. And while misinformation clearly increases some Americans’ reluctance to get vaccinated, correcting such misinformation can only go so far. There will always be some unknowns around any new drug, even one that has now had 185 million “trials” in the United States alone. And uncertainty is a powerful thing.

But uncertainty can cut both ways

To counter these effects, public health authorities — and anyone who has struggled to persuade friends and family — might consider using uncertainty and anxiety to make a case for vaccination. Because while there are some unknowns about the coronavirus vaccines, there are even more unknowns about covid-19.

Scientists and physicians have no idea, for instance, what the long-term impact of coronavirus infections will be, especially for younger patients. A number of studies raise serious concerns about the virus’s lasting damage to cardiac and lung tissue and lingering neurological symptoms. Further, researchers don’t yet know how the coronavirus will affect children over the long run, especially with early reports that pediatric hospitalizations seem to be increasing.

And as long as low vaccination rates allow the virus to keep circulating, no one can predict how it might mutate into new and more dangerous variants — as it already has done.

Framed this way, health officials can make clear that there is at least as much uncertainty about the long-term effects of covid-19 as about a vaccine — and much more alarming uncertainty, at that. The research on political anxiety suggests that this argument may resonate powerfully with many who have held out thus far.

Christopher Ray (@HegemonySnicket) is a PhD candidate studying international relations and political psychology at Ohio State University.