After having Pfizer-COVID-19 BioNTech's vaccine, a health worker in Alaska experienced an extreme allergic reaction and is now hospitalized but healthy, a study said Wednesday.

The New York Times announced that the individual was fired on Tuesday, and Pfizer stated that the company had been working to investigate the incident with local authorities.

Two health workers had similar allergic reactions in Britain, prompting the government there to tell individuals if they had a history of serious allergies to stop getting the shot.

The US regulator released an emergency approval with the warning that people who had known allergies to ingredients within the vaccine should avoid it.

"We do not yet have all the details of the Alaska report on potential serious allergic reactions, but we are actively working to evaluate them with the local health authorities," said a spokesman for Pfizer.

"We will monitor all reports suggesting serious allergic reactions following vaccination closely and if necessary, update the labeling language."

Pfizer clinical trial volunteers of 44,000 individuals were disqualified if they had a history of allergic reactions to COVID-19 vaccines or vaccine components.

Overall, no significant safety risks were found in the study, but regulators and the company continue to check for adverse effects after vaccination.

The US is vaccinating some three million people with the vaccine this week and aims to meet a total of 20 million people this month if it approves another vaccine developed by Moderna.