If you had a first-dose reaction, you might still be able to get a second dose. Among people who had a possible allergic reaction to a first dose of COVID-19 vaccine, most of those who received a second dose have tolerated the second dose well. Early in the vaccine rollout, there was a concern that people with polyethylene glycol (PEG) allergy might react to the COVID-19 mRNA vaccines. More recent data shows that many people who have reacted to other PEG-containing medications have not reacted to the mRNA vaccines.