The Pfizer vaccine was shown to be safe and about 95 percent effective in a clinical trial involving 44,000 participants. Two Alaska Fatality Report will likely intensify concerns about possible side effects. Experts said the developments may prompt calls for tighter guidelines to ensure that recipients were carefully monitored for adverse reactions.

The first worker, a middle-aged woman who had no history of allergies, had an anaphylactic reaction that began 10 minutes after receiving the vaccine at Bartlett Regional Hospital in Juneau on Tuesday, a hospital official said. She experienced a rash over her face and torso, shortness of breath and an elevated heart rate.

Dr. Lindy Jones, the hospital’s emergency department medical director, said the worker was first given a shot of epinephrine, a standard treatment for severe allergic reactions. Her symptoms subsided but then re-emerged, and she was treated with steroids and an epinephrine drip.

When doctors tried to stop the drip, her symptoms re-emerged yet again, so the woman was moved to the intensive care unit, observed throughout the night, then weaned off the drip early Wednesday morning, Dr. Jones said.

Dr. Jones had said earlier Wednesday that the woman was set to be discharged in the evening, but the hospital said late Wednesday that she was remaining another night.

The second worker received his shot on Wednesday and developed eye puffiness, light-headedness and a scratchy throat 10 minutes after the injection, the hospital said in a statement. He was taken to the emergency room and treated with epinephrine, Pepcid and Benadryl, although the hospital said the reaction was not considered anaphylaxis. The worker was back to normal within an hour and released.

The hospital, which had administered 144 total doses as of Wednesday night, said both workers did not want their experiences to have a negative impact on others lining up for the vaccine.

“We have no plans to change our vaccine schedule, dosing or regimen,” Dr. Anne Zink, Alaska’s chief medical officer, said in a statement.

But as a Caveat, Dr. Paul offit said it is important to determine what part of the vaccine contributed to the allergic reactions.