The governing body of vaccines in the UK has urged people who have a history of "significant" allergic reactions not to have the Pfizer/BioNtech COVID-19 vaccine.
The Medicines and Healthcare products Regulatory Agency (MHRA) made the decision after two NHS nurses experienced anaphylactoid reactions after receiving the jab on Tuesday - the first day of the UK's mass vaccination programme.
An anaphylactoid reaction is a severe allergic reaction that can cause difficulty breathing, face and tongue swelling, as well as light-headedness, among other symptoms. The staff members reacted shortly after the vaccine was administered.
Both nurses were said to have a history of reacting to vaccines in this way and carried adrenaline auto-injectors (injections which are to be administered in the event of an anaphylactic shock).
The two staff members are "recovering well" according to Professor Stephen Powis, national medical director for the NHS.
“As is common with new vaccines, the MHRA has advised on a precautionary basis that people with a significant history of allergic reactions do not receive this vaccination after two people with a history of significant allergic reactions responded adversely yesterday," said Powis.
The NHS has issued new advice about the Pfizer vaccine, which states: "Any person with a history of a significant allergic reaction to a vaccine, medicine or food (such as previous history of anaphylactoid reaction or those who have been advised to carry an adrenaline autoinjector) should not receive the Pfizer BioNtech vaccine.
"Resuscitation facilities should be available at all times for all vaccinations. Vaccination should only be carried out in facilities where resuscitation measures are available."
NHS England has said they "are seeking further information and will issue further advice following investigation."
While most people can expect to feel some discomfort at the injection site and possible mild flu-like symptoms after a vaccination, it is very rare to experience a severe allergic reaction, according to authorities.
As a new medicine to the UK, the vaccine is being monitored for any side effects and any suspected adverse reactions are being reported to the NHS via the Yellow Card scheme.
The UK became the first country to authorise the Pfizer/BioNtech vaccine for emergency use. It has secured 40 million doses, which can vaccinate 20 million people as two separate injections are needed for the jabs to work.
The British government will only immunise people over 16, with around 55 million people in the UK over this age bracket.