Table 4. Negative binomial regression of the association between the number of secondary cases (outcome) and intervention promptness indicators (mediators).

	Entire period(n=1884)		Before Alpha variant (n=827)
	IRR*	95% CI	IRR*	95% CI
Tracing delay	1.01	0.99–1.04	1.03	0.99–1.07
Known source of infection of the index case	0.75	0.63–0.91	0.73	0.55–0.96
Index case symptomatic	1.21	0.96–1.53	1.30	0.93–1.82

^*Adjusted for the type of school, type of index case, and class size.