Secondary attack rate (SAR) and risk for transmission by index cases reported during the Omicron epidemic in Shanghai from 1 March to 1 June 2022
| Characteristics* | Secondary cases/total close contacts (N/N) | SAR (95% CI) | Crude OR (95% CI) | Adjusted OR (95% CI)† |
| Sex of index cases | ||||
| Male | 45 163/244 240 | 18.49 (18.38 to 18.61) | 1 (Reference) | 1 (Reference) |
| Female | 37 304/206 530 | 18.06 (17.92 to 18.19) | 0.95 (0.92 to 0.97) | 0.93 (0.91 to 0.96) |
| Occupation of index cases | ||||
| Medical workers | 14 356/84 128 | 17.06 (16.84 to 17.31) | 1 (Reference) | 1 (Reference) |
| Students | 8777/48 549 | 18.08 (17.70 to 18.42) | 1.59 (1.40 to 1.81) | 1.39 (1.19 to 1.63) |
| Building workers | 5292/28 213 | 18.76 (18.21 to 19.20) | 1.77 (1.57 to 1.99) | 1.59 (1.41 to 1.79) |
| Taxi and bus drivers | 5679/27 822 | 20.41 (19.91 to 20.89) | 1.80 (1.50 to 2.17) | 1.60 (1.32 to 1.92) |
| Preschoolers | 830/5268 | 15.76 (14.79 to 16.90) | 2.16 (1.88 to 2.48) | 1.61 (1.33 to 1.96) |
| Retired | 1542/7605 | 20.28 (19.31 to 21.31) | 2.13 (1.89 to 2.39) | 1.63 (1.44 to 1.84) |
| Food market workers | 465/2250 | 20.67 (18.73 to 22.53) | 1.81 (1.59 to 2.05) | 1.66 (1.46 to 1.89) |
| Unemployed | 3038/22 646 | 13.42 (12.97 to 13.89) | 1.79 (1.59 to 2.02) | 1.69 (1.50 to 1.90) |
| Public service staff | 18 739/87 467 | 21.42 (21.13 to 21.67) | 1.96 (1.73 to 2.22) | 1.85 (1.64 to 2.10) |
| Delivery workers | 1341/9410 | 14.25 (13.55 to 15.01) | 2.09 (1.66 to 2.63) | 1.90 (1.51 to 2.40) |
| Others | 19 791/112 868 | 17.53 (17.31 to 17.73) | 1.62 (1.44 to 1.82) | 1.55 (1.38 to 1.74) |
| Severe/critical | ||||
| No | 82 411/450 482 | 18.29 (18.29 to 18.30) | 1 (Reference) | 1 (Reference) |
| Yes | 56/288 | 19.44 (14.80 to 25.23) | 1.28 (0.84 to 1.95) | 0.96 (0.64 to 1.46) |
| Self-reported symptoms | ||||
| No | 60 745/336 937 | 18.03 (17.96 to 18.10) | 1 (Reference) | 1 (Reference) |
| Yes | 21 722/113 833 | 19.08 (18.88 to 19.30) | 1.14 (1.11 to 1.18) | 1.17 (1.13 to 1.21) |
| Comorbidities | ||||
| No | 57 319/322 979 | 17.75 (17.67 to 17.83) | 1 (Reference) | 1 (Reference) |
| Yes | 25 148/127 791 | 19.68 (19.48 to 19.87) | 1.13 (1.10 to 1.16) | 0.93 (0.90 to 0.96) |
| Vaccination status of index cases | ||||
| No vaccination | 13 928/72 273 | 19.27 (18.96 to 19.55) | 1 (Reference) | 1 (Reference) |
| Partial vaccination | 1853/10 908 | 16.99 (16.16 to 17.70) | 0.93 (0.85 to 1.01) | 1.06 (0.97 to 1.16) |
| Full vaccination | 29 178/161 216 | 18.10 (17.93 to 18.26) | 0.88 (0.85 to 0.91) | 0.97 (0.93 to 1.01) |
| Booster vaccination | 37 444/206 039 | 18.17 (18.04 to 18.31) | 0.89 (0.86 to 0.92) | 0.96 (0.92 to 1.00) |
| Time from positive test to isolation | ||||
| 0 days | 1395/10 790 | 12.93 (12.30 to 13.56) | 1 (Reference) | 1 (Reference) |
| 1 days | 13667/91 274 | 14.97 (14.76 to 15.20) | 1.14 (1.04 to 1.26) | 1.17 (1.06 to 1.29) |
| 2 days | 36 539/184 589 | 19.79 (19.64 to 19.94) | 1.30 (1.18 to 1.42) | 1.35 (1.22 to 1.48) |
| 3 days | 10 860/48 953 | 22.18 (21.82 to 22.54) | 1.41 (1.28 to 1.56) | 1.50 (1.36 to 1.66) |
| 4 days | 3476/15 950 | 21.79 (21.12 to 22.55) | 1.38 (1.24 to 1.54) | 1.47 (1.32 to 1.64) |
| 5+ days | 2589/12 910 | 20.05 (19.34 to 20.89) | 1.42 (1.26 to 1.59) | 1.46 (1.30 to 1.64) |
*'Unknown’ of each characteristic was excluded from the analysis.
†Adjusted for age group, sex, occupation, comorbidities and vaccination status of index cases and close contacts; and for clinical severity, self-reported symptoms and time from positive test to isolation of index cases.