The omicron wave is finally on the decline in the U.S. Workers are returning to offices again, hospital wards are emptying, and states have lifted mask mandates. But a new strain, BA.2, has spread widely in Europe and is growing in prevalence in the U.S. And Pfizer Inc. and Moderna Inc. have now asked U.S. regulators to clear an additional Covid-19 booster as protection provided by the first three shots fades.
While the vaccines at first were remarkably good at preventing Covid infections, successive mutations and the passage of time have rendered the shots less effective. The boosters people received late last year did help ward off some Covid infections during the most recent surge, but those may not end up being the final shots for those who want to stay ahead of this virus. “It is clear that we are going to have to develop a strategy for fourth, and possibly continuing, shots,” says Arnold Monto, an epidemiologist and influenza expert at the University of Michigan who believed this during the spread of the delta variant. The emergence of omicron, he says, “only strengthens my view.”
That’s where the knowns end. Figuring out which variants future boosters should target, when the shots might be needed, and who should take them is a murky work in progress. Answers to basic questions such as how long protection from existing shots lasts and how many further variants of Covid will arise remain elusive. Future variants may not end up being better at evading the immune system, which could make additional shots unnecessary for most people. Or more harmful mutations may emerge, making the urgent development of variant-specific vaccines the better course of action.
