There are now 2 approved Covid-19 vaccines; Pfizer and Moderna. They are both mRNA vaccines and work similarly. The agent suspicious for the few but serious allergic reactions in Pfizer vaccine is polyethylene glycol (PEG) used to hold the nanoparticle messenger RNA. This is polyether compound derived from petroleum and has many applications in industrial manufacturing to medicine. Skin rash to Vaseline, Aquaphor, or products with petroleum. Check make-up, lotion, eye drop ingredients if you have had a skin rash or eye reaction to a thick-petroleum like product: redness with dry-scaly areas, and or swelling. Also, any reaction to polyethylene suture material will be a sign of an allergy to this product. Tell your doctor and/or pharmacist who will be helping you get the vaccine. During the FDA hearings for the Moderna vaccine, which I watched, Moderna says PEG is not in their vaccine, but I am investigating this information. Stay tuned.