Supplies of COVID-19 vaccines in the US are under pressure from growing demand, as previously inoculated Americans returned for their required second shots and millions of newly eligible people scrambled to get their first.
The supply gaps, coming as the US vaccination effort enters its second month, prompted some healthcare systems to suspend appointments for first-time vaccine seekers.
"As eligibility increases, you just increase demand, but we're not able to increase supply," Northwell Health spokesman Joe Kemp told Reuters.
Northwell, New York's largest healthcare provider, offers appointments only as it gets more vaccine, and only after allocating doses to people scheduled for their second shots, Kemp said.
Both approved vaccines, one from Pfizer Inc and BioNTech and the other from Moderna Inc, require a booster three to four weeks after the first shot to maximise their effectiveness against the coronavirus.
While healthcare workers and nursing home residents and staff got first priority, eligibility for the vaccines has since widened, with some states opening it to healthy people aged 65 and up and people of any age with pre-existing conditions.
Besides New York, signs of vaccine supply strains appeared in Vermont, Michigan, South Carolina, New Jersey and Oregon.
In Oregon, Governor Kate Brown said vaccinations for seniors and educators would be delayed, while Vermont Governor Phil Scott said the state would focus exclusively on its over-75 population because of "unpredictable" federal supplies.
"Rather than over-promising a limited supply to a broad population that we know we can't vaccinate all at once, we believe our strategy will get shots in arms faster and more efficiently, with less loss of life," Scott said on Twitter.
New York's Mount Sinai Hospital said on Friday that it cancelled vaccination appointments through Tuesday because of "sudden changes in vaccine supply."
An official at NYU Langone Health, another healthcare giant, said it has indefinitely suspended new appointments because it had received no confirmation that it would get more vaccine.
New York City Mayor Bill de Blasio was among three dozen big city mayors who asked the incoming Biden administration last week to send COVID-19 vaccine shipments directly to them, bypassing state governments.
Adding to the inter-governmental tension was a squabble in which several governors accused the Trump administration on Friday of deceptively pledging to distribute millions of COVID-19 vaccine doses from a stockpile that the US health secretary has since acknowledged does not exist.
Since the onset of the pandemic, 23.4 million Americans have been infected with the coronavirus, 392,153 of whom died, according to a Reuters tally.
Australian Associated Press