The desperately awaited vaccination drive against the coronavirus in the US is running into resistance from an unlikely quarter: surprising numbers of healthcare workers who have seen first-hand the death and misery inflicted by COVID-19 are refusing shots.
It is happening in nursing homes and, to a lesser degree, in hospitals, with employees expressing what experts say are unfounded fears of side effects from vaccines that were developed at record speed.
More than three weeks into the campaign, some places are registering as much as 80 per cent of the staff holding back.
"I don't think anyone wants to be a guinea pig," said Dr Stephen Noble, a 42-year-old cardiothoracic surgeon in Portland, Oregon, who is postponing getting vaccinated.
"At the end of the day, as a man of science, I just want to see what the data show. And give me the full data."
Alarmed by the phenomenon, some administrators have dangled everything from free breakfasts at Waffle House to a raffle for a car to get employees to roll up their sleeves.
Some states have threatened to let other people cut ahead of healthcare workers in the line for shots.
"It's far too low. It's alarmingly low," said Neil Pruitt, CEO of PruittHealth, which runs about 100 long-term care homes in the country's south, where fewer than three in 10 workers offered the vaccine so far have accepted it.
Many medical facilities in US states from Florida to Washington have boasted of near-universal acceptance of the shots and workers have proudly plastered pictures of themselves on social media receiving the vaccine.
Elsewhere, though, the drive has stumbled.
While the federal government has released no data on how many people offered the vaccines have taken them, glimpses of resistance have emerged around the country.
In Illinois, a big divide has opened at state-run veterans homes between residents and staff.
The discrepancy was worst at the veterans home in Manteno, where 90 per cent of residents were vaccinated but only 18 per cent of the staff members.
In rural Ashland, Alabama, about 90 of 200 workers at Clay County Hospital have yet to agree to get vaccinated, even with the place so overrun with COVID-19 patients that oxygen is running low and beds have been added to the intensive care unit, divided by plastic sheeting.
The push-back comes amid the most lethal phase in the outbreak yet, with the death toll at more than 350,000, and it could hinder the government's effort to vaccinate somewhere between 70 per cent and 85 per cent of the US population to achieve "herd immunity".
Administrators and public health officials have expressed hope that more health workers will opt to be vaccinated as they see their colleagues take the shots without problems.