The COVID-19 vaccine developed by Moderna and the National Institutes of Health caused very few cases of severe allergic reactions during the first three weeks of its administration across the country, according to a new report from the Centers for Disease Control and Prevention.
Among 4,041,396 doses administered over 21 days, a total of 10 cases of anaphylaxis were confirmed by CDC investigators. Another four cases of possible anaphylaxis are still being investigated.
No deaths were associated with the vaccine.
“Based on this early monitoring, anaphylaxis after receiving the Modern COVID-19 vaccine appears to be a rare event,” wrote the researchers on Friday in the CDC’s Weekly Morbidity and Mortality Report.
The authors calculated that there were 2.5 cases of anaphylaxis for every 1 million doses of Moderna vaccine administered. A similar study of the COVID-19 vaccine developed by Pfizer and BioNTech reported that there were 11.1 cases of anaphylaxis for every 1 million doses of that vaccine during the first 10 days of administration.
Anaphylaxis is a serious allergic reaction that can be fatal if not treated immediately. It can be triggered by a vaccine or by exposure to certain foods, medications, insect bites or latex. The usual treatment is an injection of epinephrine, which relaxes the muscles that prevent air from reaching the lungs.
The 10 cases were reported to the Vaccine Adverse Event Notification System, which the CDC maintains with the Food and Drug Administration to track safety issues that arise after vaccines are released to the public. They were spread across the country and involved different batches of vaccine.
A total of 1,266 adverse events linked to the Moderna vaccine were severe enough to be reported over the three-week period. It is a rate of 0.03%.
For comparison, the Pfizer-BioNTech vaccine had an adverse event rate of 0.2% during the first 10 days.
Here’s what the CDC researchers learned about the 10 cases of anaphylaxis:
• Patients were aged between 31 and 63, with a median of 47 years.
• All 10 patients were women. Even considering the fact that women represented more than 60% of all people who received the Modern vaccine, this distortion is notable. In general, 80% of anaphylaxis cases reported to VAERS involve women, the researchers noted.
• The average time it took for anaphylactic reactions to start was 7.5 minutes after giving the vaccine.
• Nine of the patients started experiencing symptoms within 15 minutes, including one who experienced the first symptom just 1 minute after receiving the injection. The tenth patient showed no sign of a problem until 45 minutes passed.
• Four patients were seen in an emergency room of a hospital and were then sent home.
• The remaining six patients were admitted to a hospital. Five of them ended up in an intensive care unit and four of them had to have a plastic tube stuck in their windpipe to help them breathe.
• Nine out of 10 patients had a history of allergies, including six who had previously experienced an allergic reaction to medications.
• Five patients had experienced anaphylaxis before, although none of the cases were triggered by a vaccine.
The CDC authors confirmed 43 other cases of other allergic reactions, 60% of which were considered “not serious”. Patients experienced skin rashes or itchy skin, an itchy sensation in the mouth and throat, a feeling that their throats were closing and respiratory symptoms.
Half of these patients had symptoms within 15 minutes after receiving the vaccine, and 73% of them had symptoms within half an hour.
In 60% of cases, patients had a history of allergic reactions, usually to medications or food.
The 43 patients were between 22 and 96 years old, and 91% of them were women.
The FDA granted emergency use authorization for the Moderna vaccine on December 18. The Pfizer-BioNTech vaccine was authorized for emergency use a week earlier.
The CDC advises that anyone who has an “immediate allergic reaction” to a first dose of Moderna vaccine or Pfizer-BioNTech vaccine should not receive a second dose. In addition, patients should be asked about previous allergic reactions before receiving any of the vaccines, says the agency.
Vaccination sites are advised to monitor people for up to 30 minutes after receiving their injections and to have epinephrine on hand to treat anyone who has a negative reaction to any of the vaccines.