Table 2

Table 2
Adjusted cumulative incidence risk ratios for severe SARS-CoV-2 within 28 days since reinfection, Italy, 24 August 2021–6 February 2022 (n = 206,013^a)
		Non-severe reinfection (203,874)		Severe reinfection (2,139)		Cumulative Incidence per 100,000	IRR adjusted (95% CI)	p value
		n	%	n	%	Cumulative Incidence per 100,000	IRR adjusted (95% CI)	p value
Epidemic phase^b	Delta	5,685	3	345	16	5,721	Reference
	Transition	36,111	18	404	19	1,106	0.47 (0.39–0.57)	< 0.001
	Omicron	162,078	79	1,390	65	850	0.37 (0.3–0.46)	< 0.001
Severity first diagnosis	No	195,921	96	1,584	74	802	Reference
Severity first diagnosis	Yes	7,953	4	555	26	6,523	2.86 (2.55–3.22)	< 0.001
Vaccination status	At least one dose	131,424	64	1,545	72	1,162	Reference
Vaccination status	Unvaccinated	72,450	36	594	28	813	1.07 (0.96–1.19)	0.243
Sex	Male	93,239	46	963	45	1,022	Reference
Sex	Female	110,635	54	1,176	55	1,052	0.95 (0.86–1.05)	0.285
Age group (years)	0–19	41,597	20	124	6	297	0.55 (0.44–0.68)	< 0.001
	20–39	69,717	34	378	18	539	0.98 (0.84–1.15)	0.768
	40–59	70,516	35	399	19	563	Reference
	60–79	16,513	8	643	30	3,748	5.45 (4.72–6.28)	< 0.001
	≥ 80	5,531	3	595	28	9,713	13.09 (11.21–15.29)	< 0.001
Healthcare worker	No	193,551	95	2,050	96	1,048	Reference
Healthcare worker	Yes	10,323	5	89	4	855	1.03 (0.82–1.29)	0.800
Nationality	Italian	185,573	91	1,903	89	1,015	Reference
Nationality	Non-Italian	18,301	9	236	11	1,273	1.68 (1.45–1.96)	< 0.001
^aSee Figure 1 and the Supplement, section 1 for the inclusion criteria. The number of reinfection depends on the study period. To estimate the risk of any reinfection we considered a study period that ranged from 24 August 2021 to 6 March 2022. In order to account for the disease progression within 28 days since reinfection, the study period for the estimation of the risk of SARS-CoV-2 reinfection leading to hospitalisation or death (severe reinfection) was censored on 6 February 2022. From 24 August 2021 to 6 March 2022, 249,121 reinfections were notified, whereas 206,013 is the number of reinfections notified from 24 August 2021 to 6 February 2022. ^b Epidemic phases: Delta: 24 Aug–5 Dec 2021; transition: 6 Dec 2021–2 Jan 2022; Omicron: 3 Jan–6 Feb 2022.