For a more complete understanding of allergic reactions to new vaccines – their frequency and severity – the research team reviewed the medical records of healthcare workers who received 38,895 doses of mRNA-based COVID-19 vaccines at Stanford Medicine between December 18, 2020 and January 26, 2021. Vaccinations included 31,635 doses of Pfizer vaccine and 7,260 doses of Moderna vaccine.
Researchers searched the medical records of vaccine recipients for treatment of allergic reactions and identified vaccine-related reactions. Twenty-two recipients, including 20 women, had possible allergic reactions, that is, specific symptoms starting within three hours of receiving the injections. The researchers looked for the following symptoms in the medical records of the recipients: hives; swelling of the mouth, lips, tongue or throat; shortness of breath, wheezing, or chest tightness; or changes in blood pressure or loss of consciousness. Only 17 of the 22 recipients presented reactions that met the diagnostic criteria for an allergic reaction. Three recipients received epinephrine, usually given for stronger anaphylaxis. All 22 have fully recovered.
Of the 22 recipients, 15 had a history of allergic reactions documented by a physician, including 10 to antibiotics, nine to food and eight to non-antibiotic medications. (Some recipients had more than one type of allergy.)
What is important is what we did not find, as much as what we found.
The researchers performed follow-up lab tests on 11 people to determine what type of allergic reaction they had, as well as what triggered their allergy: was it one of the inert sugar or fat ingredients in the bubble, or something else in the vaccine?
Study participants underwent skin tests, in which a clinician injected small amounts of potential allergens – lipids, sugars (polyethylene glycol or polysorbates) or the whole vaccine – into the skin. The skin test detects allergic reactions mediated by a form of antibody known as immunoglobin E or IgE; these reactions are usually associated with the most severe allergies.
None of the recipients responded to skin tests to inert vaccine ingredients, and the skin of a single recipient responded to the entire COVID-19 vaccine. Follow-up blood tests showed that vaccine recipients did not have significant levels of IgE antibodies against vaccine ingredients.
Since skin tests did not explain the mechanism of the allergic reactions of the recipients, the investigators performed another type of diagnostic test. Vaccinees provided blood samples for testing for allergic activation of immune cells called basophils. Blood samples from 10 of the 11 participants showed a reaction to the inert ingredient polyethylene glycol (PEG), which is used in both Pfizer and Moderna vaccines. Additionally, all 11 recipients exhibited basophil activation in response to whole mRNA vaccine when mixed with their own basophils.
All 11 subjects had elevated levels of IgG antibodies against PEG in their blood; IgG antibodies help activate basophils under certain conditions, and this finding suggests that individuals were likely sensitive to PEG before receiving their vaccines.
“What is important is what we didn’t find, as much as what we found,” said Nadeau. “It does not appear that the mRNA itself causes the allergic reactions.”
Additionally, the data suggests that reactions to COVID-19 vaccines were generally not the most serious form of allergic reaction, which is good news in terms of vaccine safety, she said. Allergic reactions mediated by IgG and basophils can be managed with antihistamines, fluids, corticosteroids and close monitoring, which means that many people who have had a reaction to their first dose of the vaccine can safely receive a second dose under medical supervision.
PEG is widely used as a stabilizer in household products, cosmetics and medicines, with women being more likely to be exposed to large amounts of the substance, which may be why more vaccine allergies have been observed. in women. (Repeated exposures to a substance can sometimes sensitize the immune system and cause allergies.) Since most reactions involved PEG rather than the active ingredients of the vaccine, it is likely that vaccine manufacturers could reformulate vaccines with different stabilizers less likely to cause allergies. , says Nadeau.
The other authors of the study at Stanford are research assistants Theo Snow, Alexandra Lee, Mihir Shah, Eric Smith, Evan Do and Iris Chang; Andra Blomkalns, MD, professor of emergency medicine; Brooke Betts, PharmD, clinical pharmacist; medical student Anthony Buzzanco; graduate student Joseph Gonzalez; Sharon Chinthrajah, MD, associate professor of medicine and pediatrics; laboratory director Diane Dunham; Grace Lee, MD, professor of pediatrics; Ruth O’Hara, MD, PhD, Dean of Research and Professor of Psychiatry and Behavioral Sciences; Helen Park, PharmD, clinical pharmacist with the Palo Alto Veterans Health Care System; Lisa Schilling, RN, MPH, vice president of quality, safety and clinical efficacy and quality manager at Stanford Health Care; Sayantani Sindher, MD, clinical associate professor of medicine and pediatrics; Deepak Sisodiya, PharmD, executive director of pharmaceutical services at Stanford Health Care; Mindy Tsai, DMSc, Principal Investigator in Pathology; and Stephen Galli, MD, professor of pathology and microbiology and immunology.
Nadeau is a fellow of the Stanford Institute for Immunology, Transplantation and Infection; principal researcher at the Stanford Woods Institute for the Environment; member of the Stanford Center for Innovation and Global Health; and member of the Bill Lane Center for the American West at Stanford. Nadeau and Galli are members of Stanford Bio-X. Nadeau, O’Hara and Galli are members of the Stanford Cardiovascular Institute. Nadeau and O’Hara are members of the Wu Tsai Neurosciences Institute at Stanford. O’Hara, Nadeau, Chinthrajah, Grace Lee, Sindher, and Galli are members of the Stanford Maternal and Child Health Research Institute. Galli is a fellow of the Stanford Cancer Institute.
Researchers at the Swiss Institute for Allergy and Asthma Research at the University of Zurich; the Department of the National Heart and Lung Institute at Imperial College London; and the Center in Allergic Mechanisms of Asthma, London, also contributed to this research.
The research was supported by the Centers for Cooperative Research on Asthma and Allergic Diseases (grant U19AI104209), the National Institutes of Health (grant R01AI140134), the National Institute of Allergy and Infectious Disease SARS Vaccine study (grant UM1AI10956508), the Parker Foundation, the Crown Foundation and the Sunshine Foundation.