TABLE 1.

Monthly incidence rates of COVID‐19 hospitalization among unvaccinated children by age group and by circulating SARS‐CoV‐2 variant. Kaiser Permanente Northern California, March 1, 2020 through December 31, 2022.

		Incidence a of hospitalization by SARS‐CoV‐2 circulating time period
	All period: March 1, 2020 to Dec. 31, 2022	Pre‐delta period: March 1, 2020 to June 19, 2021		Delta period: June 20, 2020 to Dec. 20, 2021		Omicron period: Dec. 21, 2021 to Dec. 31, 2022
	N = 423	N = 105		N = 85		N = 233
Age category	n (%)	n (%)	Incidence rate	n (%)	Incidence rate	n (%)	Incidence rate
<6 months	103 (24.3)	24 (22.9)	7.0	18 (21.2)	13.3	61 (26.2)	22.4
6–11 months	40 (9.5)	4 (3.8)	1.2	6 (7.1)	5.1	30 (12.9)	12.7
1 ‐ < 5 years	139 (32.9)	21 (20.0)	0.8	19 (22.4)	1.8	99 (42.5)	5.2
5 ‐ < 12 years	80 (18.9)	29 (27.6)	0.6	24 (28.2)	1.3	27 (11.6)	1.4
12 ‐ < 18 years	61 (14.4)	27 (25.7)	0.6	18 (21.2)	2.7	16 (6.9)	1.6

^a Incidence per 100,000 person‐months.