Table II.

Comparison of reported U.S. cases of mRNA vaccine anaphylaxis using different anaphylaxis rating criteria

Anaphylaxis definition	Certainty	Pfizer-BioNTech December 14–23, 2020	Moderna December 21, 2020– January 10, 2021	Non-COVID-19 vaccines 2009-2011, United States
BCC (as reported)	Levels 1-3	21 cases in 1,893,360 doses 11.1/million (95% CI 6.9-17.0)	10 cases in 4,041,396 doses 2.5/million (95% CI 1.2-4.6)	33 cases in 25,173,965 doses 1.3/million (95% CI 0.9-1.8)
BCC (reassessed)	Levels 1-3	15 cases 7.9/million (95% CI 4.4-13.1)	5 cases 1.2/million (95% CI 0.4-2.9)	31 cases 1.2/million (95% CI 0.8-1.8)
NIAID	Probable	4 cases 2.1/million (95% CI 0.6-5.4)	3 cases 1.5/million (95% CI 0.2-2.2)	18 cases 0.7/million (95% CI 0.4-1.1)
	Possible	Up to 8 cases 4.2/million (95% CI 1.8-8.3)	Up to 6 cases 1.5/million (95% CI 0.5-3.2)	Up to 31 cases 1.2/million (95% CI 0.8-1.8)
WAO	Probable	10 cases 5.3/million (95% CI 2.5-9.7)	4 cases 1.0/million (95% CI 0.3-2.5)	25 cases 1.0 /million (95% CI 0.6-1.5)
	Possible	Up to 12 cases 6.3/million (95% CI 3.2-11.1)	Up to 7 cases 1.7/million (95% CI 0.7-3.6)	Up to 31 cases 1.2/million (95% CI 0.8-1.8)

NIAID, National Institute of Allergy and Infectious Disease; WAO, World Allergy Organization.

Reprinted with permission from Hourihane JOB, Byrne AM, Blumchen K, Turner PJ, Greenhawt M. Ascertainment bias in anaphylaxis safety data of COVID-19 vaccines. J Allergy Clin Immunol Pract 2021;9:2562-6.⁸⁴