Supplementary Table 2.

Determinants of quantitative serology response – results by center

Characteristics	Bologna		Brescia		Verona
	Mean (SD) antibody level (ln(Ab)/SD)	RR (95% CI)	Mean (SD) antibody level (ln(Ab)/SD)	RR (95% CI)	Mean (SD) antibody level (ln(Ab)/SD)	RR (95% CI)
Sex
Men	6.84 (0.91)	1 (Ref)	6.50 (1.06)	1 (Ref)	6.33 (1.46)	1 (Ref)
Women	6.94 (0.87)	1.14 (0.66-1.95)	6.54 (0.98)	1.08 (1.03-1.13)	6.36 (1.41)	1.07 (1.01-1.12)
Age
10-yr increase	-	0.80 (0.78-0.82)		0.88 (0.87-0.90)	-	0.81 (0.79-0.82)
Job Title
Administration	6.79 (0.73)	1 (Ref)	6.38 (0.97)	1 (Ref)	5.98 (1.62)	1 (Ref)
Physician	6.94 (0.93)	0.85 (0.75-0.98)	6.55 (0.97)	1.01 (0.94-1.08)	6.44 (1.28)	1.06 (0.96-1.17)
Nurse	6.91 (0.91)	0.90 (0.79-1.03)	6.59 (0.99)	0.97 (0.91-1.04)	6.41 (1.45)	1.05 (0.96-1.16)
Technician	6.94 (0.75)	0.97 (0.82-1.15)	6.56 (0.99)	1.05 (0.96-1.14)	6.15 (1.34)	1.04 (0.93-1.17)
Other HCW	6.87 (0.86)	0.94 (0.82-1.07)	6.47 (1.07)	0.95 (0.89-1.02)	6.33 (1.58)	1.06 (0.96-1.17)
Previous COVID-19 infection
No	6.84 (0.86)	1 (Ref)	6.19 (0.79)	1 (Ref)	6.08 (1.18)	1 (Ref)
Yes	7.67 (0.81)	2.53 (2.31-2.78)	7.66 (0.76)	4.26 (4.07-4.45)	8.64 (1.22)	6.63 (6.17-7.13)
Time since vaccination
10-14-day interval	-	0.97 (0.94-0.99)	-	1.01 (0.90- 1.12)	-	NA
Pre-vaccination serology level
1 SD increase	-	NA	-	1.19 † (1.16-1.22)	-	1.18 † (1.15-1.21)
Time between serology tests
30-day interval	-	NA	-	1.03 † (0.98-1.08)	-	1.04 † (1.02-1.05)

CI, confidence interval; RR, relative risk for increase of 1 SD ln(Ab), adjusted for sex, age, job title and previous infection, as appropriate; Ref, reference category; NA, not available; † Additionally adjusted for pre-vaccination serology level and time between serology tests, as appropriate