ANALYSIS: Post-immunization casesare very rare and but also very expected.

Don’t Be Surprised When Vaccinated People Get Infected Post-immunization cases, sometimes called “breakthroughs,” are very rare and very expected. Katherine J. Wu The Atlantic

It’s hard to know when exactly the first cases appeared. But certainly by January’s end, a slow trickle of post-vaccination infections had begun in the United States. They arose in the West, making headlines in Oregon; they sprouted in the Midwest and the South. Some of the latest reports have come out of Florida, Texas, and Hawaii. These breakthrough cases—discovered in people more than two weeks after they received their final COVID-19 shot—will continue to grow in number, everywhere. And that’s absolutely no cause for concern.

Breakthrough infections, which occur when fully vaccinated people are infected by the pathogen that their shots were designed to protect against, are an entirely expected part of any vaccination process. They’re the data points that keep vaccines from reaching 100 percent efficacy in trials; they’re simple proof that no inoculation is a perfect preventative. And so far, the ones found after COVID-19 vaccination seem to be unextraordinary.

Since mid-December, when the rollout of the newly authorized vaccines began, nearly 40 million Americans have received the jabs they need for full immunization. A vanishingly small percentage of those people have gone on to test positive for the coronavirus. The post-shot sicknesses documented so far seem to be mostly mild, reaffirming the idea that inoculations are powerful weapons against serious disease, hospitalization, and death. This smattering of cases is a hazy portent of our future: Coronavirus infections will continue to occur, even as the masses join the ranks of the inoculated. The goal of vaccination isn’t eradication, but a détente in which humans and viruses coexist, with the risk of disease at a tolerable low.

When breakthrough cases do arise, it’s not always clear why. The trio of vaccines now circulating in the United States were all designed around the original coronavirus variant, and seem to be a bit less effective against some newer versions of the virus. These troublesome variants have yet to render any of our current vaccines obsolete. But “the more variants there are, the more concern you have for breakthrough cases,” Saad Omer, a vaccine expert at Yale, told me. The circumstances of exposure to any version of the coronavirus will also make a difference. If vaccinated people are spending time with groups of unvaccinated people in places where the virus is running rampant, that still raises their chance of getting sick. Large doses of the virus can overwhelm the sturdiest of immune defenses, if given the chance.

The human side of the equation matters, too. Immunity is not a monolith, and the degree of defense roused by an infection or a vaccine will differ from person to person, even between identical twins. Some people might have underlying conditions that hamstring their immune system’s response to vaccination; others might simply, by chance, churn out fewer or less potent antibodies and T cells that can nip a coronavirus infection in the bud. ...