“This kind of thing is pretty rampant,” Jha said. “I have personally heard stories like this from dozens of physician friends in a variety of different states. Hundreds, if not thousands, of doses are getting tossed across the country every day. It’s unbelievable.”

Jha said the ER doctor whose story he laid out in a Twitter threadthis week asked to not be identified, but his story, seen by thousands of people, resonated with other medical professionals frustrated by rules and regulations that they say are making it harder to get more Americans vaccinated.

Why is this happening? Covid-19 vaccines have a short shelf life once they are thawed out for use, Jha said. And because of federal and state mandates, hospitals and other health care providers would rather risk a dose going bad than give it to somebody who isn't scheduled to get a shot.

At the same time, states like Massachusetts now have rules requiring hospitals to report the number of vaccine doses that have been discarded, Jha said.

“The problem is that hospitals that do report this get pilloried in the press for wasting vaccines,” Jha said. “So, many hospitals are not reporting and this is happening across the country.”

While there doesn’t appear to be any solid numbers yet of how many of the Covid-19 vaccines have been discarded in the United States since the rollout began last month, the World Health Organization warned in 2005 that up to 50 percent of the vaccines released globally each year end up in the dumpster because of supply chain problems, such as not having enough freezer space or transportation issues.

For Heather Suri, a registered nurse in Virginia, the race to vaccinate Americans against COVID-19 has thrown up some unprecedented obstacles.

The vaccines themselves are delicate and require a fair bit of focus over time. Consider Moderna’s instructions for preparing its doses: Select the number of shots that will be given. Thaw the vials for 2.5 hours in a refrigerator set between 36 and 46 degrees. Then rest them at room temperature for 15 minutes. Do not refreeze. Swirl gently between each withdrawal. Do not shake. Inspect each vial for particulate matter or discoloration. Store any unused vaccine in refrigeration.

And then there’s this: Once open, a vial is good for only six hours. As vaccines go, that’s not very long. Some flu vaccine keeps almost a month.

“This is very different, administering this vaccine. The process, it takes a whole lot longer than any mass vaccination event that I’ve been involved with,” said Suri, a member of the Loudoun Medical Reserve Corps who joined her first clinic Dec. 28, to vaccinate first responders.

Of the first two COVID-19 vaccines on the market, Moderna’s is considered more user-friendly. Pfizer-BioNTech’s shot must be stored in specialized freezers at 94 degrees below zero. Once out of deep freeze, it lasts just five days, compared with 30 days for Moderna’s.

One thing the shots have in common: They last a paltry six hours once the first dose is removed from a vial. That short shelf life raises the stakes for the largest vaccination effort in U.S. history by forcing clinicians to anticipate the exact number of doses they’ll need each day. If they don’t get it right, precious stores of vaccine may go to waste.

During one recent clinic over several hours, Suri estimated she gave “maybe 25” shots, many fewer than the number of flu shots she’s given during similar clinics over the years.

With COVID-19, she said, “the vaccine itself slows things down.”