Allergic Reactions to Vaccines: What to Know About COVID, Flu, Shingles, and More
Key takeaways:
Allergic reactions to vaccines are rare. They occur in about 1 in 1 million people.
Your immune system can react to any part of the vaccine, from egg protein to stabilizers. This can happen right away or several hours later.
Anaphylaxis is the most serious type of allergic reaction. It causes difficulty breathing and a feeling like your throat is closing. Call 911 if you’re experiencing these symptoms.
Vaccines are crucial to protecting yourself and those around you from serious diseases. In the past, people often got sick — or died — from illnesses that people today have never seen thanks to vaccines. And many current vaccines target common viruses that antibiotics can’t treat.
Vaccines are safer than many media stories lead people to believe. The main risk that everyone should know about is an allergic reaction. The rate of true allergic reactions is rare — about 1 in 1 million. But because some allergic reactions can be life-threatening, it’s important that everyone knows about them.
Why do vaccines cause allergic reactions?
Your body can have an allergic reaction to any part of a vaccine. Contrary to popular belief, the part of the bacteria or virus in the vaccine is not what most people have an allergy to. The most common components of vaccines that cause reactions include:
Preservatives
Cultures from eggs and yeast
Stabilizers and other proteins
There are different types of allergic reactions, or “hypersensitivity” reactions, to vaccines. These occur when a part of your immune system gets activated by a specific ingredient in the vaccine.
This reaction can happen immediately, or it can be delayed. This is why healthcare providers ask you to wait 15 to 30 minutes after you get a vaccine. The most serious reactions happen within minutes. But reactions can occur up to 96 hours (4 days) after the vaccine is administered.
It may seem like allergic reactions to vaccines are becoming more common, especially with the COVID-19 vaccine. In reality, the rate of reactions hasn’t changed. It’s just that more vaccines are available, and more people are getting vaccinated.
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What are the signs of an allergic reaction to a vaccine?
Allergic reactions to vaccines are different from the expected side effects that can occur. And there’s a range of possible allergic reactions. Some are more annoying than harmful. Relatively mild reactions can include a rash or hives. Other reactions can be more severe or life-threatening. Let’s take a closer look.
Nonallergic reactions
Since a vaccine essentially introduces your body to a weakened or killed version of the bacteria or virus, you may feel mild symptoms as your immune system responds. This includes:
Soreness
Fatigue
Low-grade fevers
Redness in the skin where the shot was given
These are signs that your immune system is reacting normally to the shot. These are not considered allergic reactions. Over-the-counter medications like acetaminophen (Tylenol) and ibuprofen (Motrin) can help with symptoms.
Mild allergic reaction
Some allergic reactions to vaccines are mild. These are not life-threatening. Symptoms include:
Rash or hives
Nasal congestion
Cough
Abdominal pain
Vomiting or diarrhea
Joint pain
Some of these symptoms can also occur alongside more serious reactions. But there are a few extra symptoms to look out for with a severe allergic reaction.
Anaphylaxis
Anaphylaxis is the most serious type of allergic reaction. Anaphylaxis is a severe immune response to something that’s not actually an infection. It can start with symptoms like hives and throat tightness. But it can quickly worsen and include:
Lip or tongue swelling (angioedema)
Facial swelling
Feeling like you can’t breath
Wheezing, severe coughing, or shortness of breath
Dangerously low blood pressure, which can cause you to pass out, or feel like you’re going to pass out
These symptoms are a sign of a medical emergency. If you or someone is experiencing anaphylaxis to a vaccine, call 911 right away. Epinephrine, steroids, and antihistamines can be given to treat the symptoms and reverse the shock from anaphylaxis.
Even though it sounds scary, remember that true anaphylactic reactions to vaccines occur in about 1 in 1 million people. This means that the benefits of vaccines far outweigh the risks for most people.
Which vaccines are most likely to cause allergic reactions?
Any vaccine can cause an allergic reaction, but some vaccines are more common or talked about.
Allergic reactions to the COVID vaccine
The wide use of messenger RNA (mRNA) vaccines is new with COVID. Examples include the Pfizer-BioNTech and Moderna vaccines, which use mRNA technology. Experts are still learning about these vaccines, even though the technology has been in development for at least 10 years.
Based on a group of people who received the vaccine in December 2020, it looks like there might be as many as 11 serious reactions for every 1 million doses of vaccine given. The CDC has guidelines to follow if you have an allergic reaction after your COVID vaccine.
Allergic reactions to the shingles vaccine
The shingles vaccine — Shingrix — is as safe as any other vaccine. Because Shingrix can cause a very strong immune reaction, mild (nonallergic) symptoms are more common. Usually these symptoms last about 2 days and go away on their own. If you have more serious symptoms, or your symptoms don’t improve after a few days, contact your provider.
Allergic reactions to the flu vaccine
The influenza vaccine uses an egg embryo for development; so the final vaccine does have some egg protein in it. But this doesn’t mean that people with egg allergies need to avoid vaccines. Most people can still get the influenza vaccine safely, even if they have a severe egg allergy.
The only vaccine with enough egg to be more of a concern is the one for yellow fever, a mosquito-borne infection that mainly occurs in South America and Africa. If you do have an egg allergy, tell your provider before getting the vaccine so appropriate precautions can be taken. Your provider may watch you closer after you get the vaccine, or give you allergy medications as a preventive measure.
What to do if you are having an allergic reaction to a vaccine
If you’re having any symptoms that could be anaphylaxis — like difficulty breathing or swelling in the face and mouth — call 911 for immediate help. If you aren’t sure, it’s better to be safe than wait to see if the symptoms get worse.
If you think you’re having a more mild allergic reaction, without any difficulty breathing, you may not need immediate medical attention. But you should still contact your provider to let them know about your symptoms. You may need specific allergy testing to see if you have an allergy to a specific part of the vaccine.
The bottom line
Vaccines are safe and can be lifesaving. The biggest risk associated with vaccines is a severe allergic reaction. But these serious reactions are rare. If you experience any swelling around your mouth or difficulty breathing after a vaccine, call 911 as soon as possible. If you’re concerned you may be at greater risk for an allergic reaction to a vaccine, don’t hesitate to talk with your provider about your concerns.
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References
Centers for Disease Control and Prevention. (2022). COVID-19: Allergic reactions.
Centers for Disease Control and Prevention. (2023). Vaccines and preventable diseases: What everyone should know.
Chung, E. H. (2014). Vaccine allergies. Clinical and Experimental Vaccine Research.
James, J. M., et al. (1998). Safe administration of influenza vaccine to patients with egg allergy. The Journal of Pediatrics.
Kelso, J. M., et al. (2012). Adverse reactions to vaccines practice parameter 2012 update. The Journal of Allergy and Clinical Immunology.
Reber, L. L., et al. (2017). The pathophysiology of anaphylaxis. The Journal of Allergy and Clinical Immunology.
Shimabukuro, T., et al. (2021). Allergic reactions including anaphylaxis after receipt of the first dose of Pfizer-BioNTech COVID-19 vaccine. JAMA.
Wood, R. A., et al. (2008). An algorithm for treatment of patients with hypersensitivity reactions after vaccines. Pediatrics.
World Health Organization. (2023). Yellow fever.
