More than two-thirds of the 15 million coronavirus vaccines shipped within the United States have so far gone unused.
As a result, the governors of New York and Florida are vowing to penalise hospitals failing to dispense shots quickly enough.
In New York, hospitals must administer vaccines within a week of receiving them or face a fine and a reduction in future supplies, Governor Andrew Cuomo said on Monday, before announcing the state's first known case of a new, more infectious virus variant detected in Britain.
"I don't want the vaccine in a fridge or a freezer, I want it in somebody's arm," he said.
"If you're not performing this function, it does raise questions about the operating efficiency of the hospital."
New York hospitals on the whole have dispensed fewer than half their allocated doses to date but performance varied from one group of hospitals to another, Cuomo said.
The NYC Health + Hospitals system, the city's main public hospital network, has only administered 31 per cent of its allotment, compared with 99 per cent for a few private hospitals in the state.
In Florida, where officials have put senior citizens ahead of many essential workers for getting the vaccine, Governor Ron DeSantis announced a policy allocating more doses to hospitals dispensing them fastest.
"Hospitals that do not do a good job of getting the vaccine out will have their allocations transferred to hospitals that are doing a good job at getting the vaccine out," DeSantis said at a briefing.
"We do not want vaccine to just be idle at some hospital system," he added.
Florida will also deploy an additional 1000 nurses and keep state-run vaccination sites open seven days.
Cuomo's announcement the more contagious COVID variant known as B.1.1.7 had been confirmed in a man in his 60s living in a town north of Albany gave new urgency to the state's efforts to accelerate vaccinations.
At least three other US cases of the so-called UK variant have been documented since last week, one each in Florida, California and Colorado.
None of the four patients has a recent travel history, meaning the variant was likely spreading person-to-person within each of the communities where it turned up.
Neither the UK variant, nor a similarly more contagious strain first found in South Africa, is believed any more lethal than the original form of the virus.
Scientists say newly developed vaccines should be equally effective against both.
But medical experts worry the emergence of a more communicable variant could accelerate a months-long surge of infections and hospitalisations already straining US healthcare systems to their limits.
The US death toll has climbed to well over 350,000 out of more than 20 million known infections to date, with the fatality rate averaging 2600-plus lives every 24 hours over the past week.
The staggering human toll, together with an upending of daily social life and a stifling of economic activity, has made the slower-than-expected uptake of available vaccines all the more vexing to authorities.
Some of the problem has been attributed to widespread distrust of immunisations, even among some healthcare workers, owing in part to the record speed with which vaccines were developed and approved.
But some US officials also have cited a lack of adequate planning and logistical glitches.