Table 3.

Risk factors  for antibody positivity in students participating rounds 1 (a) and 2 (b) of secondary school surveillance for SARS-CoV-2, England.

OR = odds ratio; IQR = Interquartile Range; CI = confidence interval.

a)
	Antibody positive	Univariable analysis		Multivariable analysis adjusted for clustering by school (p = 1.0)
		N = 893		N = 719
Factor	n/N (%)	OR (95% CI)	P value	OR (95% CI)	P value
Sex
Female	63/532 (11.8)	REF		REF	0.86
Male	51/355 (14.4)	1.25 (0.84–1.86)	0.27	1.05 (0.63–1.73)
Non–binary/Missing	0/6 (0.0)
Year Group
Years 7–9	56/475 (11.8)	REF	0.013	REF	0.0031
Years 10–11	43/241 (17.8)	1.62 (1.06–2.50)		2.31 (1.37–3.88)
6th form/College	15/177 (8.5)	0.69 (0.38–1.26)		0.97 (0.46–2.02)
Ethnicity
White	63/567 (11.1)	REF	0.01	REF	0.15
Black	10/41 (24.4)	2.58 (1.21–5.51)		1.99 (0.73–5.46)
Asian	24/164 (14.6)	1.37 (0.83–2.27)		1.38 (0.73–2.61)
Mixed	7/73 (9.6)	0.85 (0.37–1.93)		1.04 (0.42–2.55)
Other	10/37 (27.0)	2.96 (1.37–6.41)		2.74 (1.15–6.54)
Missing	0/11 (0.0)
School area
Derbyshire	15/205 (7.3)	0.93 (0.42–2.04)	0.0042	0.85 (0.31–2.33)	0.012
East London	35/215 (16.3)	2.28 (1.14–4.56)		2.39 (0.97–5.93)
Greater Manchester	9/80 (11.3)	1.49 (0.60–3.70)		2.03 (0.71–5.85)
Hertfordshire	15/98 (15.3)	2.12 (0.95–4.75)		2.63 (0.97–7.10)
West London	28/142 (19.7)	2.89 (1.40–5.93)		3.33 (1.39–7.99)
Birmingham	12/153 (7.8)	REF		REF
Additional children in household
per additional child		0.75 (0.58–0.97)	0.027	0.77 (0.59–1.00)	0.048
median size (IQR)	1 (0–2)
Additional household members
per additional member		0.98 (0.86–1.11)	0.72
median size (IQR)	3 (3–4)
Parental occupation
Neither healthcare or key worker	71/570 (12.5)	REF	0.77
Key worker	31/245 (12.7)	1.02 (0.65–1.60)
Healthcare worker	12/78 (15.4)	1.28 (0.66–2.48)
School Capacity
per 1 increase in students per year		1.00 (0.99–1.00)	0.18
median (IQR)*	1215 (793–1500)
% FSM
per % increase in FSM		1.00 (0.98–1.02)	0.68
median (IQR) *	17.6 (9.2–20.7)
b)
	Antibody positive	Univariable analysis		Multivariable analysis adjusted for clustering by school (p = 1.0)
		N = 893		N = 878
Factor	n/N (%)	OR (95% CI)	P value	OR (95% CI)	P value
Sex
Female	62/550 (11.3)	REF		REF	0.26
Male	55/339 (16.2)	1.52 (1.03–2.25)	0.035	1.31 (0.82–2.08)
Non–binary/Missing	0/4 (0.0)
Year Group
Years 7–9	62/464 (13.4)	REF	0.0031	REF	0.18
Years 10–11	42/233 (18.0)	1.43 (0.93–2.19)		1.29 (0.82–2.04)
6th form–College	13/196 (6.6)	0.46 (0.25–0.86)		0.64 (0.31–1.32)
Ethnicity
White	72/591 (12.2)	REF	0.14	REF	0.053
Black	11/41 (26.8)	2.64 (1.27–5.50)		3.35 (1.52–7.38)
Asian	19/147 (12.9)	1.07 (0.62–1.84)		1.12 (0.61–2.05)
Mixed	10/72 (13.9)	1.16 (0.57–2.37)		1.32 (0.63–2.80)
Other	5/31 (16.1)	1.39 (0.52–3.72)		1.48 (0.53–4.12)
Missing	0/11 (0.0)
School area
Derbyshire	26/205 (12.7)	1.16 (0.60–2.25)	0.0071	1.20 (0.55–2.60)	0.60
East London	22/207 (10.6)	0.95 (0.48–1.88)		1.25 (0.54–2.93)
Greater Manchester	22/79 (27.8)	3.09 (1.51–6.32)		1.93 (0.86–4.34)
Hertfordshire	10/75 (13.3)	1.23 (0.53–2.86)		1.73 (0.57–5.19)
West London	21/183 (11.5)	1.04 (0.52–2.07)		1.45 (0.56–3.74)
West Midlands	16/144 (11.1)	REF		REF
Additional children in household
per additional child		0.94 (0.74–1.19)	0.57
median size (IQR)	1 (0–2)
Additional household members
per additional member		1.02 (0.87–1.18)	0.84
median size (IQR)	3 (3–4)
Parental occupation
Neither healthcare or key worker	79/576 (13.7)	REF	0.53
Key worker	32/249 (12.9)	0.93 (0.60–1.44)
Healthcare worker	6/68 (8.8)	0.61 (0.25–1.45)
School Capacity
Per 10 student increase		1.01 (1.00–1.01)	0.049	1.00 (0.99–1.01)	0.79
Median size (IQR) *	1215 (793–1380)
Average students year
per 1 increase in students per year		1.00 (1.00–1.00)	0.83
median (IQR) *	192 (160–300)
% FSM
per % increase in FSM		1.03 (1.01–1.06)	0.001	1.01 (0.98–1.04)	0.60
median (IQR) *	17.5 (9.2–20.7)
Number of positive cases in school
per 1 additional case		1.01 (1.01–1.02)	<0.001	1.01 (1.00–1.03)	0.027
median (IQR) *	35 (15–56)

based on included students and not school