Jan. 22 (UPI) -- Ten of the more than 4 million people in the United States who received the Moderna COVID-19 vaccine through Jan. 10 experienced a potentially life-threatening side effect, according to data released Friday by the U.S. Centers for Disease Control and Prevention.
The side effect, anaphylaxis, is a severe allergic reaction that can occur within seconds or minutes of exposure to an allergen.
Symptoms of anaphylaxis include a skin rash, nausea, vomiting, difficulty breathing and shock. In most cases, it can be treated quickly with the "epi pen."
Nearly 1,300 given the shot as of that date reported side effects as a result. All but 53 of these were considered minor, non-allergic reactions to the vaccine, such as swelling at the injection site, the CDC said.
That figure includes the 10 cases of anaphylaxis, as well as 43 other allergic reactions that include itchy skin, rash, itchy sensations in the mouth and throat, sensations of throat closure and respiratory symptoms such as shortness of breath, according to the agency.
The 10 cases of anaphylaxis all occurred in women who received the shot, half of whom had a history of having a reaction to a vaccine and all but one of whom had medication allergies, the CDC said.
The women ranged from age 31 to 63, and all but one began to experience the symptoms of anaphylaxis fewer than 15 minutes after receiving the shot, the agency said.
All 10 were treated with the epi pen, which contains the drug epinephrine, and all are believed to have recovered fully, according to the agency.
The CDC is not discouraging vaccination for people with a history of anaphylaxis, but advises them to "be observed for 30 minutes" after receiving the shot, according to Dr. Nancy Messonnier, director of CDC's National Center for Immunization and Respiratory Diseases.
All COVID-19 vaccine recipients should be observed for at least 15 minutes after getting the shot.
Vaccine facilities are also urged to be prepared to treat patients for anaphylaxis and have epi pens available in case they are needed.
People who experience an immediate reaction such as anaphylaxis after the first dose of the vaccine should not get the second, the CDC said.
Earlier this month, the CDC reported that 29 people who had received one of the two FDA-approved COVID-19 vaccines -- from Pfizer-BioNTech and Moderna -- had experienced the reaction. Those figures were through Dec. 23.
The cause of the reaction in response to the vaccines remains unknown, although both products use similar medical technologies and require two doses for maximum effectiveness.
Through Thursday, 17.5 million people in the United States had received at least one dose of the two vaccines, with 9.8 given the Pfizer-BioNTech version and 7.7 given the Moderna version, the CDC said.