MINOT, ND. – With the United States’ COVID vaccine program rolling out at a quicker pace, an increasing number of us are getting our shots against the virus. According to the latest data from the Centers for Disease Control and Prevention (CDC), as of Mar. 28, more than 51 million people in the U.S. had been fully vaccinated against COVID and more than 93 million had received at least one dose of the vaccine. Of course, that also means more people are experiencing the side effects that are expected to come along with the shot. Most of these are mild and pass quickly, but experts are warning patients to be aware of rare—but potentially more serious—reactions, particularly swelling in three specific areas after their COVID vaccine. To learn what you should be on the lookout for, read on, and for more on the latest vaccine news, check out The Only Medication You Should Take Before Your COVID Vaccine, Experts Say.

While COVID vaccine side effects may make you feel a little below par, most can be dealt with by simply resting up, staying hydrated, and using mild over-the-counter pain relievers. However, in a very small number of cases, an allergic reaction to the vaccine may take place.

The Mayo Clinic’s advice warns patients to be on alert for a “continuous shortness of breath or wheezing,” “redness, swelling or itchiness in areas of the body other than the limb in which the vaccine was given,” and particularly, “swelling of the lips, eyes or tongue.” In severe cases, where treatment with epinephrine or hospitalization is required, this is known as anaphylaxis.“You’ll likely be monitored for 15 minutes after getting a COVID-19 vaccine to see if you have an immediate reaction,” warns the CDC. And for more rare, but less alarming reactions to the vaccine, check out The Strange New COVID Vaccine Side Effect That’s Confusing Even Doctors.

If you experience this kind of severe allergic reaction, the CDC says that you should contact your doctor and not get a second shot of that vaccine. “If the reaction was after an mRNA COVID-19 vaccine (either Pfizer-BioNTech or Moderna), you should not get a second shot of either of these vaccines,” the agency says.

“An immediate allergic reaction happens within 4 hours of getting vaccinated and may include symptoms such as hives, swelling, and wheezing (respiratory distress),” the CDC notes. “Your doctor may refer you to a specialist in allergies and immunology to provide more care or advice.” And for more on the latest news about the vaccine, check out This One Side Effect Signals a “Very Robust” Vaccine Response, Doctor Says.