Table 1. Crude and adjusted risk factors for infection among contacts in the Delta-dominant period in a study of SARS-CoV-2 secondary attack rates in vaccinated and unvaccinated household contacts during replacement of Delta with Omicron variant, Spain*.

Variable	No. patients†	Crude OR			Adjusted OR‡
		OR (95% CI)	p value		OR (95% CI)	p value
Vaccination status, contacts
Vaccinated	88/167	Referent			Referent
Unvaccinated	58/84	2.00 (1.2–3.5)	0.01		5.42 (1.6–18.6)	0.007
1 dose	8/17	Referent			Referent
2 doses	77/146	1.25 (0.5–3.4)	0.7		1.26 (0.4–3.8)	0.7
3 doses	3/4	3.37 (0.3–39.3)	0.3		2.12 (0.2–27.2)	0.5
Time since vaccination, wk
1–13	11/31	Referent			Referent
14–20	20/50	1.21 (0.5–3.1)	0.7		0.98 (0.4–2.7)	0.9
21–25	32/54	2.64 (1.1–6.6)	0.04		1.74 (0.6–5.0)	0.3
>25	25/31	7.58 (2.4–24.1)	0.001		4.17 (1.1–15.3)	0.03
Missing data	0/1
Pooled		1.96 (1.4–2.8)	<0.001		1.63 (1.1–2.4)	0.01
Age of contacts, y
0–12	45/70	Referent			Referent
13–18	7/18	0.35 (0.1–1.0)	0.06		1.50 (0.3–6.8)	0.6
19–35	14/32	0.43 (0.2–1.0)	0.05		1.62 (0.4–6.4)	0.5
36–45	24/46	0.61 (0.3–1.3)	0.2		2.68 (0.7–10.1)	0.1
>45	53/81	1.05 (0.5–2.1)	0.9		4.45 (1.1–18.3)	0.04
Missing data	3/4	1.7 (0.2–16.9)	0.5
Pooled		1.03 (0.9–1.2)	0.7		1.48 (1.1–1.9)	0.003
Vaccination status, index patients
Vaccinated	114/180	Referent			Referent
Unvaccinated	32/71	0.48 (0.3–0.8)	0.009		0.30 (0.1–0.8)	0.02
Age of index patients, y
0–12	21/48	Referent			Referent
13–18	4/6	2.57 (0.4–15.4)	0.3		0.54 (0.1–4.6)	0.6
19–35	20/38	1.43 (0.6–3.4)	0.4		0.40 (0.1–1.4)	0.1
36–45	46/69	2.57 (1.2–5.5)	0.02		0.71 (0.2–2.3)	0.6
>45	55/90	2.02 (1.0–4.1)	0.05		0.57 (0.2–1.9)	0.4
Pooled		1.20 (1.0–1.4)	0.03		0.94 (0.7–1.2)	0.6
Number of housemates
<2	70/104	Referent			Referent
>2	58/116	0.52 (0.3–0.9)	0.01		0.63 (0.3–1.2)	0.1
Sex
M	79/132	Referent			Referent
F	67/118	1.13 (0.7–1.9)	0.6		1.03 (0.6–1.8)	0.9
Missing data	0/1

*OR, odds ratio. †Values are number infected/total number of patients in each strata. ‡Adjusted analysis only included participants who had all data available.