Britain has reported several cases of anaphylaxis among people who have received the Pfizer vaccine. In the U.S., 12 cases have been reported since the vaccine rollout began earlier this month, according to the CDC. Most followed receipt of the Pfizer vaccine, but a Boston doctor with a shellfish allergy developed a severe allergic reaction after receiving the Moderna vaccine. If and when other Covid vaccines are authorized for use, health authorities will be watching closely to see whether anaphylaxis is linked to all Covid vaccines, or merely those like the Pfizer and Moderna vaccines which are made using messenger RNA.
Allergies are the result of autoimmune disorders. A single change to an amino acid translated by mRNA is how these recessive conditions come about.