Omicron is setting the stage for a regularly mandated, test-and-vaccinate regime for Covid.

(Originally published Dec. 30 in “What in the World“) As Omicron continues its rampage through Europe and the U.S., it’s becoming clear that vaccination is a temporary state requiring continual renewal with boosters, up to three a year. This is a politically inconvenient realization, since most citizens were hopeful that crossing the vaccination Rubicon was a singular rite of passage out of government restrictions. So be prepared for a booster backlash as we move toward either regular booster requirements or, perhaps more intelligently, regular required tests of antibody levels.

Complicating political support for boosters is the fact that, even as infections continue to skyrocket, global deaths are falling. Many remain hopeful that this means Omicron is less lethal than previous strains, but it also seems to be to some extent due to combined levels of immunity among the people it’s infecting. Here’s an illustration:

Covid infections are racing upward in all four of these countries: Denmark, France, the United Kingdom and the United States. And of these, Denmark and the U.K. have the highest residual herd immunity, meaning the combined total of vaccinations, boosters and people who’ve had Covid-19. So in these two, deaths have been declining (despite a recent spike in Denmark, which hopefully doesn’t augur a tipping point).

But France and the U.S. have lower residual immunity, France largely because fewer people have had boosters, and the U.S. because it lags in terms of both vaccinations and boosters. France arguably is still dominated by Delta, so that might explain its rising mortality rate if Omicron is truly a less lethal strain. But Omicron is already more prevalent in the U.S., where deaths are rising, than in Denmark, where they’re falling. That supports the idea that herd immunity is to some extent working to reduce Omicron’s lethality.

Indeed, the above graph of fatality rates corresponds neatly to aggregate levels of immunity, the highest in the U.K. and the lowest in the U.S., but rising in all as more people get shots amid Omicron’s spread.