Katherine Wu in The Atlantic:
Vaccines don’t last forever. This is by design: Like many of the microbes they mimic, the contents of the shots stick around only as long as it takes the body to eliminate them, a tenure on the order of days, perhaps a few weeks.
What does have staying power, though, is the immunological impression that vaccines leave behind. Defensive cells study decoy pathogens even as they purge them; the recollections that they form can last for years or decades after an injection. The learned response becomes a reflex, ingrained and automatic, a “robust immune memory” that far outlives the shot itself, Ali Ellebedy, an immunologist at Washington University in St. Louis, told me. That’s what happens with the COVID-19 vaccines, and Ellebedy and others told me they expect the memory to remain with us for a while yet, staving off severe disease and death from the virus at extraordinary rates.
That prediction might sound incompatible with recent reports of the “declining” effectiveness of COVID-19 vaccines, and the “waning” of immunity. According to the White House, we’ll all need boosters very, very soon to fortify our crumbling defenses. The past few weeks of news have made it seem as though we’re doomed to chase SARS-CoV-2 with shot after shot after shot, as if vaccine protections were slipping through our fingers like so much sand.