Table 2.

Protection against reinfection with SARS-CoV-2 by sex, age group, and time since first infection, in the alternative cohort analysis

		Number of infections during follow-up		Infection rate*		Adjusted rate ratio (95% CI)†	Estimated protection (95% CI)	p value‡
		Exposed individuals	Unexposed individuals	Exposed individuals	Unexposed individuals
Overall		138	53 991	5·64	30·94	0·212 (0·179–0·251)	78·8% (74·9–82·1)	..
Sex
	Female	78	30 225	5·68	30·87	0·209 (0·167–0·261)	79·1% (73·9–83·3)	0·84
	Male	60	23 766	5·59	31·03	0·216 (0·168–0·279)	78·4% (72·1–83·2)	..
Age group, years
	0–34	49	26 829	5·92	38·13	0·173 (0·131–0·229)	82·7% (77·1–86·9)	<0·0001
	35–49	32	12 071	5·16	31·92	0·199 (0·141–0·282)	80·1% (71·8–85·9)	..
	50–64	26	10 111	4·25	27·42	0·187 (0·127–0·274)	81·3% (72·6–87·3)	..
	≥65	31	4980	8·01	16·92	0·529 (0·372–0·753)	47·1% (24·7–62·8)	..
Time in follow-up, months
	3–6	84	37 357	5·57	27·28	0·207 (0·167–0·256)	79·3% (74·4–83·3)	0·67
	≥7	54	16 634	2·66	14·48	0·223 (0·171–0·291)	77·7% (70·9–82·9)	..

^*Rate of infection per 100 000 person-days of follow-up.

^†Adjusted for sex, age group, test frequency, and start month of follow-up.

^‡p value from likelihood ratio tests comparing models with and without interaction terms to capture evidence of effect heterogeneity across subgroups.