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(NEXSTAR) — A small population of people are allergic to the ingredients in the three available COVID-19 vaccines, but according to Dr. Anthony Fauci, an ongoing study seeks to weigh the costs and benefits of the vaccine for those with allergies.

During an “Ask Me Anything” stint on Twitter, Fauci responded to a question asking, “Are there any alternative meds in the works for people who cannot take the current vaccines due to anaphylaxis dangers?”

Fauci said the National Institute for Allergies and Infectious Diseases “has started a study to gather information to help doctors advise people who are highly allergic or have a mast cell disorder about the risks and benefits of receiving the mRNA COVID-19 vaccines.”

According to the Centers for Disease Control and Prevention, an immediate allergic reaction typically occurs within four hours of vaccination, and may include symptoms such as hives, swelling and respiratory distress.

The CDC says if you have had a severe allergic reaction or immediate allergic reaction, even if it was not severe, to any ingredient in an mRNA COVID-19 vaccines, that you should not receive the vaccine.

The agency recommends talking to your doctor about which vaccine is safe for you, if you are allergic to the ingredients in one.

You can find more information about vaccines and allergies on the CDC website.