Table 3.

IRR and protective immunity of previous SARS-CoV-2 infection against medically attended symptomatic omicron BA.4, BA.5, and XBB reinfection, stratified by time from first infection

		Omicron BA.4 or BA.5					Omicron XBB
		Person-days at risk	Number of cases	Incidence per million person-days	IRR* (95% CI)	Protective immunity† (95% CI)	Person-days at risk	Number of cases	Incidence per million person-days	IRR* (95% CI)	Protective immunity† (95% CI)
SARS-CoV-2-naive		53 076 623	3298	62·1	1·00 (reference value)	Reference	24 498 337	36 510	1490	1·00 (reference value)	Reference
Pre-omicron
	3 to <12 months	1 708 251	98	57·4	0·86 (0·70 to 1·06)	14 (−6 to 30)	594 500	1107	1862	1·35 (1·26 to 1·43)	..
	≥12 months	1 693 303	63	37·2	1·03 (0·80 to 1·33)	..	972 008	1631	1678	1·34 (1·27 to 1·41)	..
Omicron BA.1
	3 to <8 months	2 102 381	90	42·8	0·35 (0·28 to 0·43)	65 (57 to 72)	194 201	223	1148	0·60 (0·53 to 0·68)	40 (32 to 47)
	≥8 months	4 527 852	73	16·1	0·51 (0·41 to 0·65)	49 (35 to 59)	2 882 732	3077	1067	0·73 (0·70 to 0·76)	27 (24 to 30)
Omicron BA.2
	3 to <6 months	4 791 699	45	9·4	0·13 (0·10 to 0·18)	87 (82 to 90)	2 033 272	850	418	0·26 (0·25 to 0·28)	74 (72 to 75)
	6 to <7 months	2 893 593	56	19·4	0·20 (0·16 to 0·26)	80 (74 to 84)	928 954	617	664	0·42 (0·39 to 0·45)	58 (55 to 61)
	7 to <8 months	5 372 227	61	11·4	0·26 (0·20 to 0·34)	74 (66 to 80)	2 819 806	2236	793	0·51 (0·48 to 0·53)	49 (47 to 52)
	≥8 months	614 795	0	0	..	..	607 465	502	826	0·63 (0·57 to 0·68)	37 (32 to 43)

IRR=incidence rate ratio.

^*Adjusted for age, sex, ethnicity, housing type, calendar date, vaccination status, and days since last vaccine dose.

^†Negative protective immunity estimates are not presented.