The FDA said it was closely monitoring the situation and working with disease control centers to investigate what triggered the reactions. As it investigates, the FDA works with Pfizer to update fact sheets and suggest information to reflect evolving information. The FDA said the current demand underscores the need for vaccine facilities to be able to treat any serious allergic reactions immediately.

Developed by pharmaceutical giant Fischer and German company Biotech, the vaccine has undergone months of rigorous safety reviews in randomized clinical trials involving tens of thousands of people. But the three cases of anaphylaxis – a rapid allergic reaction that can be quickly reversed with medication – are a complication for officials who expect the vaccine to gain public acceptance.

They are also a biochemical secret. No one knows which component of the vaccine induced anaphylactic reactions.

“Data aggregate now continues to support immunizations under Pfizer [emergency use authorization] These cases underscore the need for caution in the early stages of the vaccination campaign, without new restrictions, ”FDA vaccine expert Doreen Fink said at the start of a one-day meeting of the FDA Advisory Council, which is examining a similar vaccine developed by Modena that is set for urgent approval in the coming days.

“We learned about these cases through well-established security surveillance systems designed to work closely with the FDA CDC to further investigate cases in the US and to communicate our findings in a timely manner,” Fink said.

Fink said the data do not suggest that new regulations are needed to use the Pfizer-biotech vaccine. Unlike traditional vaccines, these do not contain preservatives and do not contain ingredients that are grown in chicken eggs.

Two cases involving health care workers with a history of severe allergic reactions occurred last week in the United Kingdom. After treatment, they fully recovered.

The third incident took place Tuesday at Bartlett Regional Hospital in Junau, Alaska. A health care worker who has no previous history of severe allergic reactions may experience shortness of breath, rapid heartbeat, and skin rash. The first symptoms started 10 minutes after receiving the vaccine.

The worker was treated overnight. By the next morning, she was stable, not on medication. She was hospitalized for a second night under hospital observation. “She is still encouraging colleagues to get the vaccine,” the statement said.

Anaphylaxis has been reported since the first and the nationwide distribution of vaccines began on Thursday afternoon.

Another official at Bartlett Regional Hospital, who received the vaccine, said in a statement from the city of Junau that “ten minutes after the vaccine was injected, he suffered eye fractures, mild headaches, and sore throats.” He was given a standard treatment with epinephrine, pepsid and benadryl. “Within an hour he was completely normal and released,” the statement said.

The hospital said the case was not considered anaphylaxis.

Vaccination specialist and pediatrician Paul Office at Children’s Hospital in Philadelphia said Wednesday that 1 in 1 million of all vaccines can cause severe allergies. Guidelines for this new vaccine should be monitored for at least 15 minutes after injection to determine if they have a reaction, or 30 minutes if they have a history of severe allergic reactions.

Mild side effects such as fever, headache, fatigue, and pain at the injection site have also been reported by volunteers in randomized trials, especially after the second dose, among young people with stronger and more reactive immunity. Those side effects will disappear in a day or two, which is not considered a cause for concern.

The vaccine has three components that could theoretically cause rare reactions, Modena’s chief medical officer Tal Sax said in a hearing Thursday. The National Institute of Health called an expert committee on Wednesday to discuss the possibilities.

He noted that many of the components of the modern vaccine – which are not linked to anaphylactic reactions in randomized trials – are proprietary and different from the components in the Pfizer-biotech vaccine.

“It simply came to our notice then [lipid nanoparticle] Here mRNA is distributed; So they should be similar. . . I don’t think that’s a factor that could be the culprit here, “said Sachs. “As mentioned, we will look very carefully and continue to work with colleagues to understand the system here.”

Modena executive Jacqueline Miller said Thursday that even one case of anaphylactic event has been reported, after checking a database from previous uses of the same vaccine technology in trials for eight other vaccines with 1,700 people. Shot given. The longest time delay is not directly related to the shot.

Irregular trials of Pfizer-Biotech and Modern Corona virus vaccines did not produce cases of anaphylaxis, but those trials did not allow anyone with a known allergy to any components of the vaccine to participate.

States and jurisdictions continue to deliver 2.9 million Pfizer dose allocations in the first week, and provide immunizations every day. States regularly provide data on vaccine coverage to the CDC, and the CDC is awaiting first data reports from states on vaccine administration, which began Monday.

According to the Department of Health and Human Services, more than 15 million doses were dispensed as of Thursday morning, but they were not needed.

Lori McGinley and Lena H. Sun also contributed to this report.