TABLE 3.

Seroprevalence of antibodies against SARS‐CoV‐2 spike protein Receptor Binding Domain (RBD) by COVID‐19 vaccination status and evidence of prior SARS‐CoV‐2 infection. ^a

	Total b	No. (column %) seropositive a	No. (column %) seronegative	P‐value c
Number of COVID‐19 vaccine doses d				<0.01
Unvaccinated	267	172 (13)	95 (78)
2 doses	613	595 (45)	18 (15)
3 doses	561	552 (42)	9 (7)
Confirmed or possible prior SARS‐CoV‐2 infection e				<0.01
Unvaccinated	148	138 (17)	10 (71)
2 doses	252	251 (31)	1 (7)
3 doses	429	426 (52)	3 (21)
No evidence of prior SARS‐CoV‐2 infection f				<0.01
Unvaccinated	119	34 (7)	85 (79)
2 doses	361	344 (68)	17 (16)
3 doses	132	126 (25)	6 (6)

Note: RBD, SARS‐CoV‐2 protein receptor binding domain.

^a Seropositive for SARS‐CoV‐2 Spike Protein RBD.

^b Excludes 136 participants with indeterminate serostatus for RBD (n = 7) or NP (n = 129) antibody. Twenty‐two participants with indeterminate serostatus were unvaccinated, 34 received two doses of vaccine, and 80 received three doses of vaccine.

^c P‐value for Chi‐square test comparing proportion seropositive to seronegative.

^d Vaccination status based on the 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.

^e 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.

^f Participants NP antibody seronegative without EHR‐documented or self‐reported positive COVID‐19 test >90 days before onset of current illness.