Getting COVID-19 when you’re vaccinated isn’t the same as getting COVID-19 when you’re unvaccinated.
By Katherine J. Wu
A new dichotomy has begun dogging the pandemic discourse. With the rise of the über-transmissible Delta variant, experts are saying you’re either going to get vaccinated, or going to get the coronavirus.
For some people—a decent number of us, actually—it’s going to be both.
Coronavirus infections are happening among vaccinated people. They’re going to keep happening as long as the virus is with us, and we’re nowhere close to beating it. When a virus has so thoroughly infiltrated the human population, post-vaccination infections become an arithmetic inevitability. As much as we’d like to think otherwise, being vaccinated does not mean being done with SARS-CoV-2.
Post-vaccination infections, or breakthroughs, might occasionally turn symptomatic, but they aren’t shameful or aberrant. They also aren’t proof that the shots are failing. These cases are, on average, gentler and less symptomatic; faster-resolving, with less virus lingering—and, it appears, less likely to pass the pathogen on. The immunity offered by vaccines works in iterations and gradations, not absolutes. It does not make a person completely impervious to infection. It also does not evaporate when a few microbes breach a body’s barriers. A breakthrough, despite what it might seem, does not cause our defenses to crumble or even break; it does not erase the protection that’s already been built. Rather than setting up fragile and penetrable shields, vaccines reinforce the defenses we already have,so that we can encounter the virus safely and potentially build further upon that protection.
To understand the anatomy of a breakthrough case, it’s helpful to think of the human body as a castle. Deepta Bhattacharya, an immunologist at the University of Arizona, compares immunization to reinforcing such a stronghold against assault.
Without vaccination, the castle’s defenders have no idea an attack is coming. They might have stationed a few aggressive guard dogs outside, but these mutts aren’t terribly discerning: They’re the system’s innate defenders, fast-acting and brutal, but short-lived and woefully imprecise. They’ll sink their teeth into anything they don’t recognize, and are easily duped by stealthier invaders. If only quarrelsome canines stand between the virus and the castle’s treasures, that’s a pretty flimsy first line of defense. But it’s essentially the situation that many uninoculated people are in. Other fighters, who operate with more precision and punch—the body’s adaptive cells—will eventually be roused. Without prior warning, though, they’ll come out in full force only after a weeks–long delay, by which time the virus may have run roughshod over everything it can. At that point, the fight may, quite literally, be at a fever pitch, fueling worsening symptoms.
Vaccination completely rewrites the beginning, middle, and end of this story. COVID-19 shots act as confidential informants, who pass around intel on the pathogen within the castle walls. With that info, defensive cells can patrol the building’s borders, keeping an eye out for a now-familiar foe. When the virus attempts to force its way in, it will hit “backup layer after backup layer” of defense, Bhattacharya told me.
Prepped by a vaccine, immune reinforcements will be marshaled to the fore much faster—within days of an invasion, sometimes much less. Adaptive cells called B cells, which produce antibodies, and T cells, which kill virus-infected cells, will have had time to study the pathogen’s features, and sharpen their weapons against it. While the guard dogs are pouncing, archers trained to recognize the virus will be shooting it down; the few microbes that make their way deeper inside will be gutted by sword-wielding assassins lurking in the shadows. “Each stage it has to get past takes a bigger chunk out” of the virus, Bhattacharya said. Even if a couple particles eke past every hurdle, their ranks are fewer, weaker, and less damaging.
In the best-case scenario, the virus might even be instantly sniped at by immune cells and antibodies, still amped up from the vaccine’s recent visit, preventing any infection from being established at all. But expecting this of our shots every time isn’t reasonable (and, in fact, wasn’t the goal set for any COVID-19 vaccine). Some people’s immune cells might have slow reflexes and keep their weapons holstered for too long; that will be especially true among the elderly and immunocompromised—their fighters will still rally, just to a lesser extent…