With no robust system to identify genetic variations of the coronavirus, experts warn that the United States is woefully ill-equipped to track a dangerous new mutant, leaving health officials blind as they try to combat the grave threat.

The variant, which is now surging in Britain and burdening its hospitals with new cases, is rare for now in the United States. But it has the potential to explode in the next few weeks, putting new pressures on American hospitals, some of which are already near the breaking point.

WASHINGTON — Federal officials and drugmakers, faced with a slower-than-expected rollout of the coronavirus vaccine, are racing to find ways to expand the supply, looking at lowering the required dosage and extracting more doses from the supplies they have.

Just weeks into the vaccine program, scientists at the National Institutes of Health and the drugmaker Moderna are analyzing data to see if they can double the supply of the company’s coronavirus vaccine by cutting doses in half. The study, though long planned, is increasingly urgent in the face of looming shortages as the country tries to fight off a surging pandemic.