Table 3.

Model-based estimates of secondary attack rates and odds ratios reflecting covariate effects on susceptibility and infectivity

		Mean incubation period: 5 days		Mean incubation period: 7 days
		Maximum infectious period: 13 days	Maximum infectious period: 22 days*	Maximum infectious period: 13 days	Maximum infectious period: 22 days
Secondary attack rate
Overall		10·4% (10·1–10·7)	15·6% (15·2–16·0)	12·3% (11·9–12·6)	17·1% (16·7–17·5)
Odds of household transmission
Household size (vs two people)
	3–4	0·60 (0·57–0·63)	0·59 (0·56–0·62)	0·59 (0·56–0·62)	0·58 (0·55–0·61)
	5–6	0·41 (0·38–0·43)	0·40 (0·37–0·42)	0·39 (0·37–0·42)	0·39 (0·36–0·41)
	>6	0·32 (0·29–0·36)	0·31 (0·28–0·35)	0·31 (0·28–0·35)	0·30 (0·27–0·34)
Epidemic phase (vs Jan 24–Feb 10)
	Before Jan 24	0·74 (0·69–0·79)	0·72 (0·68–0·77)	0·79 (0·74–0·84)	0·77 (0·73–0·82)
	After Feb 10	0·86 (0·77–0·96)	0·86 (0·77–0·95)	0·63 (0·56–0·70)	0·62 (0·56–0·69)
Odds of infection for an exposed household contact (susceptibility)
Age group, years (vs ≥60)
	0–1	0·34 (0·23–0·51)	0·34 (0·23–0·51)	0·34 (0·23–0·51)	0·34 (0·23–0·51)
	2–5	0·16 (0·13–0·19)	0·16 (0·13–0·20)	0·16 (0·13–0·19)	0·16 (0·13–0·19)
	6–12	0·22 (0·19–0·26)	0·22 (0·19–0·26)	0·22 (0·19–0·26)	0·22 (0·19–0·26)
	13–19	0·27 (0·23–0·31)	0·27 (0·23–0·31)	0·27 (0·23–0·31)	0·27 (0·23–0·31)
	20–39	0·50 (0·48–0·53)	0·51 (0·48–0·54)	0·50 (0·48–0·53)	0·50 (0·48–0·53)
	40–59	0·69 (0·65–0·72)	0·69 (0·66–0·72)	0·68 (0·65–0·72)	0·69 (0·65–0·72)
Female sex (vs male)		1·11 (1·06–1·16)	1·11 (1·07–1·16)	1·11 (1·06–1·16)	1·11 (1·06–1·16)
Odds of onwards transmission for an infective case (infectivity)
Age group, years (vs ≥60)
	<20	1·65 (1·32–2·05)	1·58 (1·28–1·95)	1·41 (1·13–1·77)	1·38 (1·11–1·72)
	20–39	1·12 (1·02–1·22)	1·10 (1·02–1·20)	1·08 (0·99–1·17)	1·07 (0·99–1·16)
	40–59	1·02 (0·95–1·09)	1·02 (0·95–1·09)	1·02 (0·95–1·08)	1·02 (0·96–1·09)
Female sex (vs male)		0·97 (0·91–1·04)	0·98 (0·92–1·04)	0·97 (0·91–1·03)	0·97 (0·91–1·03)
Disease severity: severe or critical (vs mild or moderate)		0·91 (0·84–0·98)	0·92 (0·85–0·98)	0·94 (0·88–1·01)	0·94 (0·88–1·00)
Diagnosis: clinical (vs RT-PCR)		0·75 (0·70–0·80)	0·75 (0·70–0·80)	0·73 (0·69–0·78)	0·74 (0·69–0·78)
Asymptomatic infection (vs symptomatic)
	Up to Feb 1	0·88 (0·36–2·14)	0·42 (0·17–1·04)	0·61 (0·28–1·33)	0·29 (0·13–0·65)
	From Feb 2	0·53 (0·38–0·76)	0·21 (0·14–0·31)	0·39 (0·27–0·56)	0·16 (0·11–0·24)
Before symptom onset (vs after symptom onset)		0·76 (0·68–0·85)	1·42 (1·30–1·55)	1·46 (1·31–1·63)	2·92 (2·67–3·19)

Data are secondary attack rate (95% CI) or odds ratio (95% CI). Overall secondary attack rates, regardless of characteristics of the infector, infectee, or household, were estimated with a separate model with fewer covariates than the model used to estimate odds ratios (appendix p 30), as some covariates will change the interpretation of the secondary attack rate. Estimates of baseline daily transmission probabilities within households and from an external source, as well as estimates of daily transmission probabilities between different age groups within households, are shown in the appendix (pp 32–33).

^*Primary analysis.