Table 2.
Risk of SARS-CoV-2 infection for individuals with natural immunity compared with individuals with no immunity
|
Natural immunity (n=1 019 553) |
No immunity (n=1 019 553) |
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=2 039 106) | 31 272 | 17·9 | 54 368 | 34·2 | 0·54 (0·53–0·55) | 0·52 (0·52–0·53) | |
| 3–6 months (n=1 477 887) | 1814 | 1·4 | 33 014 | 29·3 | 0·05 (0·05–0·05) | 0·04 (0·04–0·05) | |
| 6–9 months (n=783 767) | 700 | 0·7 | 7588 | 8·9 | 0·08 (0·08–0·09) | 0·08 (0·07–0·09) | |
| ≥9 months (n=303 236) | 304 | 0·6 | 4198 | 8·5 | 0·07 (0·06–0·08) | 0·07 (0·06–0·08) | |
| ≥3 months (n=1 477 887) | 2818 | 1·7 | 44 800 | 31·2 | 0·06 (0·05–0·06) | 0·05 (0·05–0·05) | |
| Events after ≥3 months follow-up, by sex | |||||||
| Male (n=722 657) | 1151 | 1·4 | 22 790 | 32·9 | 0·05 (0·04–0·05) | 0·04 (0·04–0·04) | |
| Female (n=755 230) | 1667 | 2·0 | 22 010 | 29·6 | 0·07 (0·06–0·07) | 0·06 (0·06–0·07) | |
| Events after ≥3 months follow-up, by age | |||||||
| <50 years (n=1 102 189) | 2070 | 1·6 | 37 775 | 35·3 | 0·05 (0·05–0·06) | 0·04 (0·04–0·05) | |
| 50–64 years (n=274 315) | 547 | 2·0 | 6139 | 23·4 | 0·08 (0·08–0·09) | 0·08 (0·07–0·09) | |
| 65–79 years (n=74 090) | 103 | 1·5 | 563 | 7·8 | 0·20 (0·16–0·25) | 0·18 (0·15–0·23) | |
| ≥80 years (n=27 305) | 98 | 4·3 | 323 | 8·4 | 0·55 (0·44–0·70) | 0·42 (0·33–0·53) | |
| Events after ≥3 months follow-up in those receiving homemaker service (N=19 324)† | 104 | 4·3 | 258 | 12·9 | 0·33 (0·26–0·41) | 0·32 (0·25–0·40) | |
| Events after ≥3 months follow-up in those with any comorbidity (n=441 752)† | 974 | 2·1 | 11 551 | 26·9 | 0·08 (0·07–0·08) | 0·07 (0·07–0·08) | |
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 613 days (mean 164 days [SD 100]). IR=incidence rate.
*
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.