The CDC guidelines now say that anyone who has previously suffered an immediate allergic reaction of any severity to any ingredient of Pfizer or Moderna's vaccines should not be vaccinated unless they have been cleared by doctors.
One ingredient that is being carefully examined is called polyethylene glycol. It's a compound that's used to stabilize and transport bubble for the messenger RNA in the vaccines.
It has never been used in a vaccine before, but it is an ingredient in many drugs. The CDC also said anyone with an allergy to polysorbate should not get the shots. It's an ingredient used to stabilize some drugs, foods and cosmetics.
Polysorbate is not an ingredient in the vaccines, but people who are sensitive to it may also be sensitive to polyethylene glycol.
Experts said people with serious allergies to foods or medications can get vaccinated. But they should be observed for 30 minutes afterward, instead of just 15. They also need to get the shot in a facility that can immediately treat an allergic reaction.
The CDC said anyone who suffers a severe allergic reaction to the first dose of the COVID-19 vaccine should not receive a second dose.
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