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Study finds no danger of second COVID shot in those with allergic reactions to first dose

Study supports the safety of second dose of Pfizer-BioNTech or Moderna vaccine in patients who reported immediate and potentially allergic reactions after the first dose.

DALLAS – August 2, 2021 – People who had a potentially allergic reaction to their first messenger RNA COVID-19 vaccination can safely receive their second shot, according to a study of patients conducted at several medical centers, including UT Southwestern.

Results of the study, involving more than 159 patients who were perceived to have had allergic reactions to their first shot of Moderna or Pfizer-BioNTech vaccine and then received their second shot, are detailed in a research letter published in JAMA Internal Medicine. Twenty percent reported immediate and potentially allergic symptoms, but the symptoms resolved on their own or with antihistamines.

The findings should give the public even greater confidence in the COVID-19 vaccines, said David Khan, M.D., Professor of Internal Medicine in the Division of Allergy and Immunology, and Program Director of UT Southwestern’s Allergy and Immunology Fellowship Program.

“Most of the other reports involve a handful of patients. This carries greater weight because it is the largest series that has been published and benefits from data from multiple institutions,” said Dr. Khan, who oversaw UT Southwestern’s participation in the study, which included researchers at Massachusetts General Hospital and Brigham and Women’s Hospital, Vanderbilt University Medical Center, and Yale School of Medicine.

“This multisite U.S. study supports the safety of Pfizer-BioNTech or Moderna vaccine second- dose administration in patients who report immediate and potentially allergic reactions after the first dose. Although mild symptoms were reported in 20% of patients with second-dose administration, all patients who received a second dose safely completed their vaccination series and could use mRNA COVID-19 vaccines in the future when indicated. Second-dose tolerance following reactions to the first dose argues that either many of these initial reactions are not all truly allergic reactions, or supports an allergic, but non-immunoglobulin E–mediated mechanism in which symptoms can typically be abated with premedications.”

  • S. Krantz, J.H. Kwah, C.A. Stone, et al. Safety Evaluation of the Second Dose of Messenger RNA COVID-19 Vaccines in Patients With Immediate Reactions to the First Dose. JAMA Internal Medicine. Published online July 26, 2021.

About UT Southwestern Medical Center

UT Southwestern, one of the nation’s premier academic medical centers, integrates pioneering biomedical research with exceptional clinical care and education. The institution’s faculty has received six Nobel Prizes, and includes 25 members of the National Academy of Sciences, 16 members of the National Academy of Medicine, and 13 Howard Hughes Medical Institute Investigators. The full-time faculty of more than 2,800 is responsible for groundbreaking medical advances and is committed to translating science-driven research quickly to new clinical treatments. UT Southwestern physicians provide care in about 80 specialties to more than 117,000 hospitalized patients, more than 360,000 emergency room cases, and oversee nearly 3 million outpatient visits a year.