“The perception magnifies what’s actually going on biologically,” Dr. Pulliam said. “It’s just that there are more people who are eligible for reinfection.”
The Omicron variant was different enough from Delta, and Delta from earlier versions of the virus, that some reinfections were to be expected. But now, Omicron seems to be evolving new forms that penetrate immune defenses with relatively few changes to its genetic code.
“This is actually for me a bit of a surprise,” said Alex Sigal, a virologist at the Africa Health Research Institute. “I thought we’ll need a kind of brand-new variant to escape from this one. But in fact, it seems like you don’t.”
An infection with Omicron produces a weaker immune response, which seems to wane quickly, compared with infections with previous variants. Although the newer versions of the variant are closely related, they vary enough from an immune perspective that infection with one doesn’t leave much protection against the others — and certainly not after three or four months.
Still, the good news is that most people who are reinfected with new versions of Omicron will not become seriously ill. At least at the moment, the virus has not hit upon a way to fully sidestep the immune system.
“That’s probably as good as it gets for now,” Dr. Sigal said. “The big danger might come when the variant will be completely different.”
Each infection may bring with it the possibility of long Covid, the constellation of symptoms that can persist for months or years. It’s too early to know how often an Omicron infection leads to long Covid, especially in vaccinated people.