Britain’s medical regulator announced that people with a history of significant allergic reactions should not have the Pfizer-BioNTech COVID-19 vaccine.

The United Kingdom's Medicines and Healthcare Products Regulatory Agency (MHRA), which is responsible for ensuring that medicines and medical devices work and are acceptably safe, said the advice applies to those who have had reactions to medicines, food, or vaccines.

The advice comes after two U.K. National Health Service (NHS) workers had allergic reactions on Tuesday.

“Any person with a history of anaphylaxis to a vaccine, medicine or food should not receive the Pfizer-BioNTech vaccine,” MHRA Chief Executive June Raine said in a statement.

“Most people will not get anaphylaxis and the benefits in protecting people against COVID-19 outweigh the risks... You can be completely confident that this vaccine has met the MHRA’s robust standards of safety, quality, and effectiveness.”

Anaphylaxis is a serious and life-threatening allergic reaction that is triggered by the overreaction of the body’s immune system.

The two staff members, who both had a history of allergic reactions, experienced symptoms of anaphylaxis after receiving the vaccine.

In the wake of the incident, MHRA also advised that vaccines "should only be carried out in facilities where resuscitation measures are available."

In a statement, Pfizer said it had been advised by the UK regulator of "two yellow card reports that may be associated with allergic reactions" due to the administration of the vaccine.

"As a precautionary measure, the MHRA has issued temporary guidance to the NHS while it conducts an investigation in order to fully understand each case and its causes. Pfizer and BioNTech are supporting the MHRA in the investigation," the statement said.

The United Kingdom became the first country to grant emergency use authorization of the vaccine developed by BioNTech, a German biotechnology company, and Pfizer, an American pharmaceutical corporation   A 90-year-old woman, Margaret Keenan, was the world’s first person to receive a vaccination to prevent the deadly disease.

On the other hand, the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) continue to assess the findings.

The FDA is poised to give a go-ahead for the emergency use of the BioNTech-Pfizer vaccine by week’s end.

Meanwhile, Canada Health earlier announced its decision authorizing the use of the Pfizer-BioNTech COVID-19 vaccine after a thorough and independent review.

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