A few days later, Moderna said it was okay to resume using that batch. Last month, the U.S. Food and Drug Administration said it was investigating severe allergic reactions to Pfizer's vaccine "in multiple states." Those reactions were reported by healthcare workers after receiving their first injection, and were believed to have resulted from an allergy to polyethylene glycol, or PEG, a compound used in the Pfizer and Moderna COVID vaccines. So far, in the U.S. only the Pfizer-BioNTech and Moderna vaccines, both of which use mRNA technology, have received emergency use authorization. By the FDA's own definition, the vaccines are considered experimental. Children's Health Defense urges anyone who suffers any reaction to any vaccine to report it following these steps.