When the omicron variant of COVID-19 emerged in South Africa late last year, it took only weeks to overtake delta, the variant that previously dominated. Then the original version of omicron was replaced by one subvariant, and then another. The latest subvariants, BA.4 and BA.5, are now quickly spreading in the U.S.
The virus is evolving so quickly that when Moderna recently announced preliminary results from the trial of its newest COVID-19 vaccine—the first designed to target both the original virus and omicron—the vaccine was already somewhat outdated since it wasn’t designed to stymie the newest subvariants. And when the Food and Drug Administration (FDA) meets at the end of June to discuss whether the vaccine should be modified before the likely rollout of more booster shots in the fall, it will have to make decisions without knowing how the virus will continue to change.