This is, in some ways, a mea culpa.
For the past year or so, I’ve been reporting on the COVID-19 vaccines, a job that’s required me to convey, again and again, how inoculations work to boost immunity and why. The shots are new, and immunology is complex. So I, like so many others in journalism and science, turned to analogies to help make the ideas of disease prevention and public health tangible. Vaccines, as I’ve written, protect us a lot like umbrellas block out the rain, sunscreens shield us from burns and cancers, and castle guards fend off raids.
Analogies, metaphors, similes, and the like are evocative and memorable. They transform the abstract into the concrete. And they very often work, especially when used to depict a virus or an infection, which are almost entirely unseen. But a lot of the ideas we link to COVID-19 vaccines—including plenty I’ve used—don’t totally hit the mark. Too many focus on vaccines’ individual perks. And they end up skating over one of the greatest benefits of immunization: a boost in wellness at the community level, by cutting down on transmission and, by extension, illness for everyone else. For immunization to truly pack a punch, Amanda Simanek, a social epidemiologist at the University of Wisconsin at Milwaukee, told me, “we all have to do it.”
Unfortunately, communal benefit is harder to define, harder to quantify, and harder to describe than individual protection, because “it’s not the way Americans are used to thinking about things,” Neil Lewis, a behavioral scientist and communications expert at Cornell, told me. That’s in part because communal risk isn’t characteristic of the health perils people in wealthy countries are accustomed to facing: heart disease, stroke, diabetes, cancer. Maybe that’s part of why we gravitate toward individual-focused comparisons. Slipping into a pandemic-compatible, population-based frame of mind is a big shift. In the age of COVID-19, “there’s been a lot of focus on the individual,” Lewis told me. That’s pretty at odds “with how infection works.”
Analogy aside, this is how a vaccine does its job: Each inoculation contains a harmless mimic of a pathogen that immune cells memorize. Vaccines “ready the immune system” so the body isn’t caught unaware when the real thing comes along, Jennifer Gommerman, an immunologist at the University of Toronto, told me. After vaccination, immune cells are faster and more efficient; they can vanquish viruses before serious illness sets in. That’s vaccination’s big objective. But vaccines also curb the number of infectious particles that exit the body to infect someone else. When this pattern gets repeated over and over, viruses start to run out of viable hosts—making it harder for them to spread, and reducing the burden of disease for everyone. Months of evidence show all of this is true of the COVID-19 vaccines.
Immunizations also work best when their limits aren’t being constantly tested. To be fair, a lot of analogies describe this dynamic quite well. Post-vaccine infections and illnesses will depend, to some degree, on the physiology of the individual, in the same way that sunscreen won’t have as much staying power on a person who’s extremely fair-skinned. But they will be more likely to happen in people exposed to gobs of virus, in the same way that folks carrying umbrellas will still probably get wet in a hurricane. Those events will also be more frequent with certain viral variants, in the same way that even well-armored castles might fall to a particularly powerful invader.
Neither sunshine nor rain nor war, however, is truly infectious, not in the way a virus is, and this very important dimension is where personal-risk analogies start to tank. One person’s decision to eschew a seat belt, airbag, or life jacket rarely affects someone else’s fate. This language is very much in keeping with the United States’ pandemic response, which, as my colleague Ed Yong has written, prioritized individualism, exceptionalism, and free will. We turn to individualistic analogies because they are culturally salient. But they can end up being an “extreme mismatch,” Lewis told me: At heart, public health is a collective endeavor, from which no one is exempt.
I’ve seen attempts to course-correct. Twitter is rife with accusations that remaining unvaccinated is akin to drunk driving, smoking, or harming children. But these comparisons, while hinting at communal risk, can backfire. “We know that shaming of any kind just doesn’t work,” Cora Scott, the director of public information and civic engagement for the city of Springfield, Missouri, told me. Cast as enemies, people “shut down and stop listening,” Lewis said. Analogies like these also misportray the unvaccinated, many of whom haven’t been able to access their shots, or are still ineligible, or haven’t been given accurate information about the vaccine and the seriousness of COVID-19.
Scott, who leads vaccine outreach efforts in her community, told me she’s been favoring a different analogy: casting the spread of infection as fire, and humans as the kindling that the flames need to persist. I’ve tried this one myself, and vaccines fit in nicely, too. They’re sprays of flame retardant that can waylay fire on the move, while also shielding vegetation from the worst of the burn. The more trees are protected, the sooner the fire has nowhere left to go.
Another option: thwarting bugs with insecticides, given that curbing an infestation in one apartment slashes the chances that it will move next door. Michael D. L. Johnson, an immunologist at the University of Arizona, offers a vivid alternative—installing a toilet in lieu of defecating in a bucket “and smearing it over your front lawn,” which would make the neighbors very unhappy and potentially seriously sick.
The point isn’t really to converge on the perfect vaccine analogy. I’m not sure one exists; no single comparison can speak to all questions, concerns, and enthusiasms about vaccination. Analogies can also falter against fear and distrust. Many of the people who are holding out on getting their shots are worried about the dangers the vaccines could pose to them as individuals. Here, experts bring in other outreach and communication strategies, including fielding individual questions, reducing barriers to access, sharing stories from within a community, and tapping local leaders as trustworthy sources. Johnson has also been working to equip friends, colleagues, and family members with the skills to detect and avoid misinformation. “I want them to be able to vet the science for themselves,” he told me.
Maybe the ideal analogy remains elusive for another reason: Nothing really is quite like a vaccine. Vaccines leverage the body’s natural capability to stave off pathogens, and stymie the serious symptoms of disease. They make bodies inhospitable to infectious threats, by buttressing the immune system’s in-house tactics. They accomplish that simply, often through just one or two brief injections that teach immune cells the nature of a particular threat, sometimes conferring protection that lasts a lifetime. They do all of this without exposing someone to an actual virus, and reduce the chances that someone else will be exposed. On an individual level, vaccines “make the immune system smart,” Gommerman told me. On a population level, they make it possible to safely coexist with a virus.
Most people don’t have to think about the many shots they received as children, because those immunizations successfully tamed a threat. When vaccines work, people stop noticing them. And that makes vaccines, quite frankly, better than any fire preventative, umbrella, sunscreen, airbag, seat belt, insecticide, or military-grade weapon I can think of. All figurative comparisons fall short in some way because vaccines are, literally, one of the best tools for protection that we have ever invented.