India is in the throes of a devastating surge in COVID-19 cases. The wave of infections, propelled by a new variant of the coronavirus, could spill into the United States. Indeed, the Indian variant—“lineage” is the scientific term—is already here.

With most states reopening and governors and mayors relaxing mask mandates as pandemic fatigue sets in, realistically just one thing can spare Americans from another spike in cases, experts say.

The country must double down on its successful vaccination campaign. Getting tens of millions more jabs in arms in the coming weeks could block the new lineage’s transmission pathways—and stop it cold.