In December, the FDA approved two COVID vaccines (Pfizer/BioNTech and Moderna) for Emergency Use Authorization and they are now being distributed across the country. There have been a small number of allergic reactions reported upon initial rollout both in the United States and in the U.K. Aleena Banerji, MD, clinical director, Allergy and Clinical Immunology at Massachusetts General Hospital, Kim Blumenthal, MD, MSc, quality and safety officer for Allergy at Massachusetts General Hospital, Rebecca Saff, MD, PhD, training program director of Allergy and Clinical Immunology at Massachusetts General Hospital, and Anna Wolfson, MD, director of Quality Assurance and Improvement of Allergic and Clinical Immunology at Massachusetts General Hospital, and colleagues in the Allergy & Clinical Immunology departments at Mass General and Brigham and Women’s Hospital offer guidance and answers to common questions regarding these initial reports of allergic reaction.

What is the concern regarding allergic reactions to the COVID-19 vaccines?

On December 9, 2020, it was reported that two patients in the U.K. had an allergic reaction after getting the COVID-19 vaccine. As of December 28, 2020, at least 10 allergic reactions to the Pfizer/BioNTech and two allergic reactions to Moderna vaccines have been reported. Very little information about the cause of these reactions are known, but to date all patients have recovered. While we still need more information to understand the risk of allergic reactions to the COVID-19 vaccine, currently the concern is low due to the small number of reactions reported among the individuals who have been vaccinated.

Which patients should speak to a physician before receiving the vaccine?

In the vaccine trials, only patients with a history of severe adverse reaction associated with a vaccine or severe allergic reaction to any component of the vaccine were excluded.  

We suggest allergy/immunology consultation if you have the following issues:

  1. Prior history of vaccine allergy with reactions such as itching, rash, hives, swelling/angioedema, wheezing, shortness of breath, chest tightness, or anaphylaxis
  2. History of allergy to polyethylene glycol (PEG) or polysorbate, with reactions such as itching, rash, hives, swelling/angioedema, wheezing, shortness of breath, chest tightness or anaphylaxis
  3. Idiopathic anaphylaxis (anaphylaxis with unknown cause)
  4. Other anaphylaxis history (such as to an injectable medication)

Do I have to avoid the COVID-19 vaccine if I have a food or drug allergy?

No, increased rates of reaction to the COVID-19 vaccine in patients with food, drug, latex venom allergy from the clinical trial data have not been reported. Patients with allergic conditions, such as food, drug, latex, venom or other allergic disorders, were not excluded. Patients with a history an anaphylaxis history of an unrelated medication or food are advised to be observed for 30 minutes after vaccination. 

What is polyethylene glycol and what common products contain polyethylene glycol?

Polyethylene glycol (PEG) is a common, water-soluble ingredient in a wide variety of commercial products including some vaccines and more than 1,000 FDA approved medications.  It is the primary ingredient in commonly used colonoscopy preparations (Golytely) or constipation treatment (Miralax) as well as in IV medications such as PEGylated medications.  It is also in ultrasound gel and depot steroid injections such as methylprednisolone acetate. Reactions to PEG are rare but anaphylaxis has been reported. PEG is the main component allergists suspect may be causing the rare anaphylaxis cases to the Pfizer/BioNTech and Moderna vaccines.

Will the COVID-19 vaccines be safe and effective?

Yes. In the U.S. the FDA reviews data from development of the vaccine and clinical trial data before approving the vaccine for use. Both vaccines that received Emergency Use Authorization from the FDA have been shown in clinical studies to be more than 94% effective. As people receive the vaccine, the FDA continues to closely monitor its safety and effectiveness.

What is a vaccine allergy? 

Similar to medications or antibiotics, people can be allergic to vaccines. However, allergic reactions to vaccines are rare. Allergic reactions to vaccines most often start within minutes following the vaccination and are characterized by the same symptoms as allergic reactions to foods or medications. This can include skin symptoms (urticaria, swelling, itching), respiratory symptoms (cough, difficulty breathing, wheezing) or more severe symptoms like a reduction in blood pressure or anaphylaxis.

Sometimes vaccines can cause local reactions that begin in the hours following vaccination or even the next day. The site of vaccination (usually the arm) can become inflamed, red and painful. The reaction can last several days. Although these reactions can be quite worrisome, they are not felt to be an allergic reaction. There is generally no risk of an allergic reaction with any subsequent vaccinations people may receive. Consultation with an allergist is not necessary.

What are common causes of a vaccine allergy?

Different components of vaccines including gelatin, egg and excipients can cause vaccine allergy.  Some people may be allergic to the rubber stopper on the vial or syringe rather than the vaccine itself. However, most manufacturers have moved away from latex rubber stoppers and now use synthetic rubber-like materials. Overall, allergic reactions to these components remain very rare.

What might happen if I have a reaction to the COVID vaccine?

If an allergic reaction occurs, depending on the symptoms that occur, a person can be treated immediately with antihistamines or epinephrine (if severe symptoms). It is important that the person suffering from the allergic reaction be referred to an allergist for further evaluation. Most of the time, allergy skin testing can confirm the allergy to the vaccine, and the resulting information can be very helpful for future vaccination. Testing in this case will include skin testing to the common inactive ingredients in the mRNA vaccines (PEG and polysorbates). In general, most patients allergic to one vaccine can receive other vaccinations without problems.

If I have a reaction to the first dose can I have the second dose?

If you have an allergic reaction with the first dose, we suggest allergy evaluation before the second dose. If you have a large local reaction with symptoms of pain, burning or swelling at the site of injection, this usually does not require allergy evaluation before the second dose. Other reactions may require a longer observation period or skin testing assessment.

Should I worry about local skin reactions to the vaccine that may develop several days after receiving the first dose?

Local injection site pain, itching, redness and swelling can occur and is not felt to be an allergic reaction. Delayed reactions with pain, redness and swelling at the injection site have been seen up to 7 to 10 days after vaccination. These delayed reactions are also not allergic reactions and do not impact the ability of the patient to receive the second dose of vaccine. In fact, these delayed reactions are a sign that your immune system is working well.

Are reactions and/or potential for allergic reactions worse after the second dose?

Based on what we know so far from the clinical trial data and personal experience, most individuals will have mild, short-term side effects after getting a COVID-19 vaccine including fever, fatigue, headache, muscle pain and joint pain and this may be worse after the second dose. The current COVID-19 vaccines are different from other vaccinations with the need for a second dose within 3 to 4 weeks. We do not have data to answer this question yet but we are working to understand this exact issue. We hope to have more information as more individuals receive the second injection.

Can individuals receiving the vaccine take Tylenol / Ibuprofen without causing reaction or it interfering with the production of antibodies?

Acetaminophen, like Tylenol, and NSAIDs, like Ibuprofen, are very effective in managing post-vaccine adverse effects including fever, muscle aches and local injection site pain. However, there are data showing meloxicam can decrease antibody responses in mice. The CDC does not recommend pre-vaccine administration of acetaminophen or NSAIDs.

I would like to volunteer for a trial. Can you tell me where to find more information?

A full list of trials can be found on the National Institute of Allergy and Infectious Diseases website

Where can I learn more about how vaccines work?

If you want to learn more about vaccines and the COVID-19 vaccine, Galit Alter, PhD, MGH Research Scholar at Mass General Research Institute offers additional information on the science behind vaccines in the videos below:


Date originally posted: 01/05/2021
Date updated: 01/14/2021