Which brings us to one of the most important unknowns about Omicron: To what extent will an Omicron infection confer immunity against other strains?

Here is the best-case scenario—keeping in mind that we don’t have nearly enough data yet: Omicron infections tend to be milder than Delta infections. The case fatality rate and infection fatality rate for Omicron are significantly lower than for Delta. Omicron winds up conferring some protection against Delta and other strains of COVID. And Omicron’s heightened infectiousness allows it to outcompete Delta and replace Delta as the dominant strain of COVID. In this scenario—in the long run—Omicron could wind up saving lives on balance by replacing Delta with a less deadly but more infectious version of COVID. A significant percentage of those who wouldn’t have survived Delta will survive Omicron and then have some protection against Delta and future variants. It is even possible to imagine a scenario in which Omicron could be the means by which COVID moves from pandemic to endemic—by quickly ensuring that almost everybody in the world is at least partially “immunized.”

The enormous uncertainties surrounding immunity and reinfection make it impossible to know how likely this optimistic scenario is. But a few scientists and public health experts have been willing to discuss that possibility, with the requisite hedging and caveats. Here’s Monica Gandhi of UCSF in New York magazine: “Omicron could still be really bad—we don’t know yet—but in the best case scenario it would hasten the time when we’re all immune and the pandemic essentially comes to an end.” And the new German health minister, Karl Lauterbach, speculated a few weeks ago that Omicron may be a “Christmas gift” if it makes the pandemic end sooner.