Key Takeaways

  • Among 52,805 health care employees who received mRNA COVID-19 vaccines, 2% experienced allergic reactions, and anaphylaxis occurred at a rate of 2.47 per 10,000 individuals.
  • All vaccine recipients who experienced anaphylaxis recovered without going into anaphylactic shock or requiring a breathing tube.

It is critical to have accurate information on allergic reactions to these vaccines, not only for our current situation, but also because this new vaccine platform is so important for future pandemic responses.

Kimberly Blumenthal, MD, MSc
Division of Rheumatology, Allergy and Immunology, Massachusetts General Hospital

BOSTON – Almost immediately after the first mRNA-based COVID-19 vaccines were authorized for emergency use and were administered to individuals outside of clinical trials, reports of anaphylaxis—a life-threatening whole-body allergic reaction—raised widespread concerns among experts and the public. Now, real world data on vaccinations among employees at Mass General Brigham provide reassurances of the rarity of such serious reactions, and the ability to recover from them. The findings are published in the Journal of the American Medical Association.

“The COVID-19 mRNA vaccines are the first vaccines of their kind, and they have remarkable efficacy and safety across all populations. It is critical to have accurate information on allergic reactions to these vaccines, not only for our current situation, but also because this new vaccine platform is so important for future pandemic responses,” says lead author Kimberly Blumenthal, MD, MSc, co-director of the Clinical Epidemiology Program within Massachusetts General Hospital’s Division of Rheumatology, Allergy and Immunology.

With this in mind, Blumenthal and her colleagues decided to carefully document all allergic reactions, including anaphylaxis, once they began employee vaccinations at Mass General Brigham. The team analyzed employee surveys to estimate the incidence of allergic reactions after mRNA vaccines and used multiple surveillance methods to identify the true incidence of anaphylaxis.

Among 52,805 employees (including an estimated 4,000 with significant allergies to foods and medications) who were surveyed after they received their first dose of an mRNA COVID-19 vaccine, 2% experienced allergic reactions, and anaphylaxis occurred at a rate of 2.47 per 10,000 individuals. “To put this in perspective, this is largely comparable to anaphylactic reactions from common antibiotics,” says Blumenthal.  

The investigators noted that although the incidence of anaphylaxis was higher than that estimated by the Centers for Disease Control and Prevention—which put the rate at 0.025 to 0.11 per 10,000 vaccinations—it is still exceedingly low and should provide reassurances, especially for individuals with a history of food or drug allergies. “The only allergy exclusion for vaccination was a prior episode of anaphylaxis to an inactive ingredient in the vaccine, called polyethylene glycol, or a cross-reactive inactive ingredient called polysorbate,” says co-senior author Paige Wickner, MD, MPH, medical director of the Department of Quality and Safety at Brigham and Women’s Hospital. “Another important aspect of our study is that all of our anaphylaxis cases recovered—no one had anaphylactic shock or required a breathing tube, even temporarily.”

The other co-senior author is Adam B. Landman, MD, of the Department of Emergency Medicine at the Brigham. The other authors are Lacey B. Robinson, MD, MPH, and Aleena Banerji, MD, of MGH’s Division of Rheumatology, Allergy and Immunology; Carlos A. Camargo, Jr., MD, DrPH, of MGH’s Department of Emergency Medicine; and Erica S. Shenoy, MD, PhD, of MGH’s Division of Infectious Diseases.

About the Massachusetts General Hospital
Massachusetts General Hospital, founded in 1811, is the original and largest teaching hospital of Harvard Medical School. The Mass General Research Institute conducts the largest hospital-based research program in the nation, with annual research operations of more than $1 billion and comprises more than 9,500 researchers working across more than 30 institutes, centers and departments. In August 2020, Mass General was named #6 in the U.S. News & World Report list of "America’s Best Hospitals."

About Brigham and Women’s Hospital
Brigham Health, a global leader in creating a healthier world, consists of Brigham and Women's Hospital, Brigham and Women’s Faulkner Hospital, the Brigham and Women’s Physicians Organization and many related facilities and programs. With more than 1,000 inpatient beds, approximately 60,000 inpatient stays and 1.7 million outpatient encounters annually, Brigham Health’s 1,200 physicians provide expert care in virtually every medical and surgical specialty to patients locally, regionally and around the world. An international leader in basic, clinical and translational research, Brigham Health has nearly 5,000 scientists, including physician-investigators, renowned biomedical researchers and faculty supported by over $700 million in funding. The Brigham’s medical preeminence dates back to 1832, and now, with 19,000 employees, that rich history is the foundation for its commitment to research, innovation, and community. Boston-based Brigham and Women’s Hospital is a teaching affiliate of Harvard Medical School and dedicated to educating and training the next generation of health care professionals. For more information, resources, and to follow us on social media, please visit

About Mass General Brigham
Mass General Brigham is an integrated academic healthcare system, uniting great minds to solve the hardest problems in medicine for our communities and the world. Mass General Brigham connects a full continuum of care across a system of academic medical centers, community and specialty hospitals, a health insurance plan, physician networks, community health centers, home care, and long-term care services. Mass General Brigham is a non-profit organization committed to patient care, research, teaching, and service to the community. In addition, Mass General Brigham is one of the nation’s leading biomedical research organizations, with several Harvard Medical School teaching hospitals. For more information, please visit