TABLE 5.

Adjusted ^a vaccine effectiveness against COVID‐19 by SARS‐CoV‐2 variant stratified by prior infection status. ^b

	Vaccination c	Total	SARS‐CoV‐2 positive	% positive	Adjusted a VE [95% CI]
Overall
No prior infection	Unvaccinated	135	60	44	Referent
	2 doses	389	129	33	17 [−40, 51]
	3 doses	207	57	28	53 [10, 76]
With prior infection	Unvaccinated	154	45	29	Referent
	2 doses	258	57	22	42 [−1, 66]
	3 doses	434	107	25	55 [21, 74]
Delta variant
No prior infection	Unvaccinated	43	14	33	Referent
	2 doses	189	20	11	70 [11, 90]
	3 doses	31	1	3	NE d
With prior infection	Unvaccinated	37	5	14	Referent
	2 doses	83	8	10	23 [−225, 82]
	3 doses	33	1	3	NE d
Omicron variant
No prior infection	Unvaccinated	74	38	51	Referent
	2 doses	157	93	59	−53 [−205, 23]
	3 doses	162	53	33	23 [−72, 65]
With prior infection	Unvaccinated	109	38	35	Referent
	2 doses	158	47	30	45 [−4, 70]
	3 doses	371	104	28	57 [20, 76]

Abbreviations: CI, confidence interval; NE, not estimates; VE, vaccine effectiveness.

^a Models adjusted for age, sex, race/ethnicity, site, illness onset week, self‐reported chronic medical condition, and high‐risk SARS‐CoV‐2 exposure.

^b Includes seropositive nucleocapsid protein (NP) antibody assay, electronic medical record documented positive SARS‐CoV‐2 molecular or antigen test, or participant self‐report of positive SARS‐CoV‐2 positive laboratory test >90 days before onset of current illness.

^c Vaccination status based on number of doses documented in electronic medical record received ≥14 days before illness onset for the second dose or ≥7 days before illness onset for the third dose.

^d Adjusted vaccine effectiveness not estimated due to too few cases.