Table 1. General characteristics of breakthrough cases and unvaccinated cases.

Characteristics			Breakthrough cases (n = 869)	Unvaccinated cases (n = 139)	χ2	P value
Age, yr
	Mean ± SD		7.72 ± 1.86	8.82 ± 2.04	6.33a	< 0.001
	Age group, No. (%)				50.58	< 0.001
		1–3	15 (1.7)	2 (1.4)
		4–6	210 (24.2)	14 (10.1)
		7–9	487 (56.0)	62 (44.6)
		10–12	157 (18.1)	61 (43.9)
Sex, No. (%)					0.4972	0.481
	Male		478 (55.0)	72 (51.8)
	Female		391 (45.0)	67 (48.2)
Reporting source, No. (%)					4.1068	0.128
	Kindergarten		131 (15.1)	13 (9.4)
	Elementary school		724 (83.3)	122 (87.8)
	Unknown		14 (1.6)	4 (1.6)

SD = standard deviation.

^at-value.