Table 1. Demographic Characteristics of the Study Cohort (Person-Days) Stratified by Prior SARS-CoV-2 Infection and Vaccination Status.
| Variable | No. (%) | |||||
|---|---|---|---|---|---|---|
| No prior SARS-CoV-2 infection (13 360 044 person-days of observation) | Prior SARS-CoV-2 infection (7 655 912 person-days of observation)a | |||||
| Unvaccinated person-days at risk | Partially vaccinated person-days at riskb | Fully vaccinated person-days at riskc | Unvaccinated person-days at risk | Partially vaccinated person-days at riskb | Fully vaccinated person-days at riskc | |
| Total person-days at risk | 12 532 687 (100) | 519 177 (100) | 308 180 (100) | 7 208 375 (100) | 446 247 (100) | 1290 (100) |
| Sex | ||||||
| Female | 6 169 824 (49.2) | 256 348 (49.4) | 147 530 (47.9) | 3 518 229 (48.8) | 219 704 (49.2) | 742 (57.5) |
| Male | 6 362 863 (50.8) | 262 829 (50.6) | 160 650 (52.1) | 3 690 146 (51.2) | 226 543 (50.8) | 548 (42.5) |
| Age distribution, y | ||||||
| 1 | 2 366 119 (18.9) | 58 068 (11.2) | 26 020 (8.4) | 1 456 023 (20.2) | 41 467 (9.3) | 96 (7.4) |
| 2 | 3 500 080 (27.9) | 119 581 (23.0) | 63 922 (20.7) | 2 010 471 (27.9) | 104 421 (23.4) | 347 (26.9) |
| 3 | 3 874 142 (30.9) | 176 482 (34.0) | 101 962 (33.1) | 2 099 851 (29.1) | 144 256 (32.3) | 528 (40.9) |
| 4 | 2 792 346 (22.3) | 165 046 (31.8) | 116 276 (37.7) | 1 642 030 (22.8) | 156 103 (35.0) | 319 (24.7) |
| Ethnicity | ||||||
| Chinese | 8 213 824 (65.5) | 356 068 (68.6) | 224 567 (72.9) | 4 654 521 (64.6) | 282 032 (63.2) | 992 (76.9) |
| Indian | 1 140 756 (9.1) | 36 615 (7.1) | 20 271 (6.6) | 552 636 (7.7) | 29 126 (6.5) | 0 (0.0) |
| Malay | 2 624 369 (20.9) | 106 157 (20.4) | 50 872 (16.5) | 1 803 338 (25.0) | 122 788 (27.5) | 256 (19.8) |
| Otherd | 553 738 (4.4) | 20 337 (3.9) | 12 470 (4.0) | 197 880 (2.7) | 12 301 (2.8) | 42 (3.3) |
| Housing type | ||||||
| 1-3 Room public housing | 7 765 136 (62.0) | 313 009 (60.3) | 184 567 (59.9) | 4 744 535 (65.8) | 289 807 (64.9) | 706 (54.7) |
| 4-5 Room public housing | 2 065 845 (16.5) | 85 003 (16.4) | 47 159 (15.3) | 1 338 389 (18.6) | 86 955 (19.5) | 323 (25.0) |
| Private housing | 2 701 706 (21.6) | 121 165 (23.3) | 76 454 (24.8) | 1 125 451 (15.6) | 69 485 (15.6) | 261 (20.2) |
| Time since last vaccination dose | ||||||
| Mean time since last dose, median (IQR), d | NA | 37 (19-61) | 41 (23-63) | NA | 62 (34-95) | 46 (25-66) |
| ≤5 wk | NA | 246 824 (47.5) | 131 265 (42.6) | NA | 119 317 (26.7) | 485 (37.6) |
| >5 wk | NA | 272 353 (52.5) | 176 915 (57.4) | NA | 326 930 (73.3) | 805 (62.4) |
| Comorbidities | ||||||
| None | 12 317 576 (98.3) | 509 404 (98.1) | 301 786 (97.9) | 7 049 235 (97.8) | 437 582 (98.1) | 1121 (86.9) |
| ≥1 Pediatric CCCe | 215 111 (1.7) | 9773 (1.9) | 6394 (2.1) | 159 140 (2.2) | 8665 (1.9) | 169 (13.1) |
| Immunocompromised statusf | ||||||
| No | 12 531 298 (100) | 519 079 (100) | 307 980 (99.9) | 7 206 095 (100) | 446 105 (100.0) | 1239 (96.0) |
| Yes | 1389 (0) | 98 (0) | 200 (0.1) | 2280 (0) | 142 (0) | 51 (4.0) |
Abbreviations: CCC, complex chronic condition; ICD-10, International Statistical Classification of Diseases and Related Health Problems, Tenth Revision; mRNA, messenger RNA; NA, not applicable.
Prior SARS-CoV-2 infection was defined as either positive polymerase chain reaction or rapid antigen test result in national records before study onset.
Partial vaccination was defined as having received at least 1 dose of mRNA vaccines but not having completed a full vaccination regimen.
Full vaccination was defined as having a primary vaccination series of 2 doses of mRNA-1273 (Moderna), or 3 doses of BNT162b2 (Pfizer-BioNTech) vaccine, at a recommended interval of 8 weeks apart, with 7 or more days having elapsed since the final dose.
Includes individuals of other ethnicities or mixed ethnicities.
Comorbidity was defined as the presence of a pediatric CCC, using ICD-10 diagnosis codes for cardiovascular, respiratory, kidney, gastrointestinal, neurologic, metabolic, congenital, and hematologic/immunologic conditions and malignancies.
Immunocompromised status was defined as the presence of solid malignancy, hematologic malignancy, rheumatologic or inflammatory disorders, other immunodeficiency, or organ or stem-cell transplant.