Rare Allergic Reactions to mRNA-Based COVID-19 Vaccines: A Study at Stanford University

Strategic Insights -

Allergic reactions to the new mRNA-based COVID-19 vaccines are rare and typically mild, and should not deter people from becoming vaccinated, according to research from the Stanford University School of Medicine. The study analyzed 22 potential allergic reactions to the first 39,000 doses of Pfizer and Moderna COVID-19 vaccines given to health care providers at Stanford soon after the vaccines received emergency use authorization from the Food and Drug Administration. The study's findings suggest that most of the allergic reactions were caused by an indirect activation of allergy pathways, making them easier to mitigate than many allergic responses.

Key Takeaways:

  • The study found that estimated rates of severe vaccine-related anaphylaxis are 4.7 and 2.5 cases per million doses for the Pfizer and Moderna vaccines, respectively.
  • The study analyzed 22 potential allergic reactions to the first 39,000 doses of Pfizer and Moderna COVID-19 vaccines given to health care providers at Stanford.
  • Most of the allergic reactions (15 out of 22) had physician-documented histories of prior allergic reactions, including allergies to antibiotics, foods, and nonantibiotic medications.
  • Follow-up laboratory testing found that skin-prick tests did not detect allergic reactions to the inert ingredients in the vaccines, and that only one recipient's skin reacted to the whole COVID-19 vaccine.
  • Blood tests showed that the vaccine recipients did not have significant levels of IgE antibodies against the vaccine ingredients, and that all 11 subjects had high levels of IgG antibodies against PEG, a stabilizer used in both the Pfizer and Moderna vaccines.
  • The data suggest that reactions to the COVID-19 vaccines were generally not the most severe form of allergic reaction, which is good news in terms of vaccine safety.
  • Most reactions were to PEG rather than the vaccine's active ingredients, making it likely that vaccine manufacturers can reformulate the vaccines with different stabilizers that are less likely to cause allergies.
  • The study suggests that allergic reactions to the mRNA-based COVID-19 vaccines are unlikely to be caused by the mRNA itself, and that reformulating the vaccines could reduce the risk of allergic reactions.
  • The study's findings are consistent with the notion that the inert ingredients in the vaccines are responsible for the allergic reactions.

Statistics:

  • 22 potential allergic reactions were identified among the 39,000 doses of Pfizer and Moderna COVID-19 vaccines given to health care providers at Stanford.
  • 17 of the 22 recipients had reactions that met diagnostic criteria for an allergic reaction.
  • 15 out of 22 recipients had physician-documented histories of prior allergic reactions.
  • 11 out of 22 recipients underwent follow-up laboratory testing, which found that skin-prick tests did not detect allergic reactions to the inert ingredients in the vaccines.
  • 10 out of 11 subjects had high levels of IgG antibodies against PEG, a stabilizer used in both the Pfizer and Moderna vaccines.
  • Estimated rates of severe vaccine-related anaphylaxis are 4.7 and 2.5 cases per million doses for the Pfizer and Moderna vaccines, respectively.

Sources:

  • [1] Nadeau, K. et al. (2021). "Allergic reactions to mRNA-based COVID-19 vaccines." JAMA Network Open, 4(9), e2124582.
  • [2] Stanford University School of Medicine. (2021). "Stanford researchers find most allergic reactions to mRNA-based COVID-19 vaccines are minor."
  • [3] NewsRx. (2021). "Rare allergic reactions to mRNA-based COVID-19 vaccines: A study at Stanford University."