Table 3.

Risk of COVID-19 hospitalisation for individuals with natural immunity compared with individuals with no immunity

		Natural immunity (n=1 018 636)		No immunity (n=1 018 636)		Hazard ratio (95% CI)
		Number of events	IR per 100 000 person-days	Number of events	IR per 100 000 person-days	Adjusted for age and baseline date	Fully adjusted*
Follow-up time in total cohort
	14 days to 3 months (n=2 037 272)	3065	3·6	1030	1·3	3·21 (2·98–3·45)	3·02 (2·80–3·26)
	3–6 months (n=1 546 582)	77	0·06	632	0·53	0·12 (0·09–0·15)	0·11 (0·09–0·14)
	6–9 months (n=773 806)	28	0·03	190	0·21	0·18 (0·12–0·26)	0·15 (0·10–0·22)
	≥9 months (N=260 984)	25	0·06	124	0·27	0·28 (0·18–0·42)	0·22 (0·15–0·34)
	≥3 months (n=1 546 582)	130	0·08	946	0·63	0·14 (0·12–0·17)	0·13 (0·11–0·16)
Events after ≥3 months follow-up, by sex
	Male (n=756 942)	80	0·10	548	0·75	0·15 (0·12–0·19)	0·14 (0·11–0·17)
	Female (n=789 640)	50	0·06	398	0·51	0·13 (0·10–0·18)	0·12 (0·09–0·16)
Events after ≥3 months follow-up, by age
	<50 years (N=1 160 812)	27	0·02	420	0·37	0·06 (0·04–0·09)	0·06 (0·04–0·09)
	50–64 years (n=283 569)	46	0·17	338	1·3	0·13 (0·10–0·18)	0·12 (0·09–0·17)
	65–79 years (n=74 643)	43	0·65	92	1·3	0·50 (0·35–0·71)	0·43 (0·29–0·63)
	≥80 years (n=27 558)	14	0·62	96	2·5	0·25 (0·14–0·45)	0·17 (0·10–0·31)
Events after ≥3 months follow-up in those receiving homemaker service (n=19 626)†		27	1·0	77	3·5	0·26 (0·16–0·43)	0·22 (0·13–0·36)
Events after ≥3 months follow-up in those with any comorbidity (n=459 097)†		87	0·19	615	1·2	0·18 (0·17–0·93)	0·16 (0·13–0·20)

In each matched pair, the baseline date for both individuals was set as the date of the first documented previous infection in the individual with natural immunity. Outcome events were traced from 14 days after baseline until a maximum follow-up of 588 days (mean 165 days [SD 95]).

^*Adjusted for age, baseline date, sex, marital status, homemaker service, place of birth, education, and comorbidities according to table 1.

^†Comparison is with the total population. IR=incidence rate.