The US Centers for Disease Control and Prevention says it has identified 21 cases of anaphylaxis, or a strong allergic reaction, among some 1.9 million people who were vaccinated against the coronavirus.
In a report on COVID-19 released on Wednesday, the CDC says about 1.9 million people had received the vaccine developed by US company Pfizer and its German partner BioNTech as of December 23.
It noted that 62 percent of them are women, 34 percent are male, and the rest are unknown.
The report also says 17 of the 21 patients had a documented history of allergies or allergic reactions.
It added that their median age was 40, and 90 percent of them are women. They usually developed symptoms in 2 to 150 minutes and 70 percent of them had an onset of symptoms within 15 minutes. It says 20 of the 21 patients have fully recovered.
A senior CDC official says that anaphylaxis caused by a coronavirus vaccine is a rare outcome. The official also says the CDC will continue to monitor the health of the vaccinated people for a certain period in case there are severe allergic reactions.
The CDC is urging people not to get a shot if they are allergic to the components of a vaccine.