Table 1. Characteristics of Omicron and Delta Cases and SARS-CoV-2–Negative Controlsa.
| Characteristic | SARS-CoV-2–negative controls (n = 114 087)b | Omicron cases (n = 16 087)b | Standardized differencec,d | Delta cases (n = 4261)b | Standardized differencec,e |
|---|---|---|---|---|---|
| Age, mean (SD), y | 42.0 (16.5) | 36.0 (14.1) | 0.39 | 44.2 (16.8) | 0.13 |
| Age group, y | |||||
| 18-29 | 30 947 (27.1) | 6813 (42.4) | 0.32 | 960 (22.5) | 0.11 |
| 30-39 | 28 387 (24.9) | 3467 (21.6) | 0.08 | 941 (22.1) | 0.07 |
| 40-49 | 19 007 (16.7) | 2821 (17.5) | 0.02 | 851 (20.0) | 0.09 |
| 50-59 | 16 695 (14.6) | 1922 (11.9) | 0.08 | 679 (15.9) | 0.04 |
| 60-69 | 11 109 (9.7) | 723 (4.5) | 0.21 | 450 (10.6) | 0.03 |
| 70-79 | 5386 (4.7) | 233 (1.4) | 0.19 | 269 (6.3) | 0.07 |
| ≥80 | 2556 (2.2) | 108 (0.7) | 0.13 | 111 (2.6) | 0.02 |
| Sex | |||||
| Female | 67 884 (59.5) | 8249 (51.3) | 0.17 | 2199 (51.6) | 0.16 |
| Male | 46 203 (40.5) | 7838 (48.7) | 0.17 | 2062 (48.4) | 0.16 |
| Any comorbidityf | 49 201 (43.1) | 5844 (36.3) | 0.14 | 1898 (44.5) | 0.03 |
| SARS-CoV-2 tests within 3 mo before Dec 14, 2020, No. | |||||
| 0 | 83 457 (73.2) | 12 448 (77.4) | 0.10 | 3473 (81.5) | 0.20 |
| 1 | 21 860 (19.2) | 2782 (17.3) | 0.05 | 615 (14.4) | 0.13 |
| ≥2 | 8770 (7.7) | 857 (5.3) | 0.10 | 173 (4.1) | 0.15 |
| Receipt of 2019-2020 and/or 2020-2021 influenza vaccine | 40 597 (35.6) | 4012 (24.9) | 0.23 | 1053 (24.7) | 0.24 |
| Public health unit regiong | |||||
| Central East | 9139 (8.0) | 831 (5.2) | 0.11 | 373 (8.8) | 0.03 |
| Central West | 21 191 (18.6) | 3899 (24.2) | 0.14 | 864 (20.3) | 0.04 |
| Durham | 7690 (6.7) | 1050 (6.5) | 0.01 | 191 (4.5) | 0.10 |
| Eastern | 7010 (6.1) | 865 (5.4) | 0.03 | 256 (6.0) | 0.01 |
| North | 7518 (6.6) | 265 (1.6) | 0.25 | 313 (7.3) | 0.03 |
| Ottawa | 5716 (5.0) | 979 (6.1) | 0.05 | 99 (2.3) | 0.14 |
| Peel | 12 592 (11.0) | 2547 (15.8) | 0.14 | 526 (12.3) | 0.04 |
| Southwest | 12 888 (11.3) | 998 (6.2) | 0.18 | 814 (19.1) | 0.22 |
| Toronto | 21 732 (19.0) | 3102 (19.3) | 0.01 | 542 (12.7) | 0.17 |
| York | 8148 (7.1) | 1476 (9.2) | 0.07 | 266 (6.2) | 0.04 |
| Household income quintileg,h | |||||
| 1 | 17 605 (15.4) | 1908 (11.9) | 0.10 | 786 (18.4) | 0.08 |
| 2 | 20 783 (18.2) | 2532 (15.7) | 0.07 | 784 (18.4) | 0 |
| 3 | 22 516 (19.7) | 3085 (19.2) | 0.01 | 840 (19.7) | 0 |
| 4 | 24 861 (21.8) | 3773 (23.5) | 0.04 | 906 (21.3) | 0.01 |
| 5 | 27 795 (24.4) | 4707 (29.3) | 0.11 | 925 (21.7) | 0.06 |
| Essential workers quintileg,i | |||||
| 1 | 26 896 (23.6) | 4539 (28.2) | 0.11 | 648 (15.2) | 0.21 |
| 2 | 28 043 (24.6) | 4487 (27.9) | 0.08 | 973 (22.8) | 0.04 |
| 3 | 22 737 (19.9) | 3057 (19.0) | 0.02 | 903 (21.2) | 0.03 |
| 4 | 19 614 (17.2) | 2272 (14.1) | 0.08 | 834 (19.6) | 0.06 |
| 5 | 16 034 (14.1) | 1621 (10.1) | 0.12 | 866 (20.3) | 0.17 |
| Persons per dwelling quintileg,j | |||||
| 1 | 21 183 (18.6) | 2523 (15.7) | 0.08 | 711 (16.7) | 0.05 |
| 2 | 19 168 (16.8) | 1934 (12.0) | 0.14 | 738 (17.3) | 0.01 |
| 3 | 15 197 (13.3) | 1919 (11.9) | 0.04 | 577 (13.5) | 0.01 |
| 4 | 27 853 (24.4) | 4143 (25.8) | 0.03 | 1026 (24.1) | 0.01 |
| 5 | 29 879 (26.2) | 5443 (33.8) | 0.17 | 1169 (27.4) | 0.03 |
| Self-identified visible minority group quintileg,k,l | |||||
| 1 | 16 930 (14.8) | 1439 (8.9) | 0.18 | 779 (18.3) | 0.09 |
| 2 | 20 294 (17.8) | 2235 (13.9) | 0.11 | 882 (20.7) | 0.07 |
| 3 | 22 577 (19.8) | 3408 (21.2) | 0.03 | 841 (19.7) | 0 |
| 4 | 26 063 (22.8) | 4250 (26.4) | 0.08 | 795 (18.7) | 0.10 |
| 5 | 27 463 (24.1) | 4644 (28.9) | 0.11 | 928 (21.8) | 0.05 |
| Week of test | |||||
| Dec 6 to Dec 12, 2021 | 31 103 (27.3) | 729 (4.5) | 0.65 | 1444 (33.9) | 0.14 |
| Dec 13 to Dec 19, 2021 | 41 090 (36.0) | 5049 (31.4) | 0.10 | 1830 (42.9) | 0.14 |
| Dec 20 to Dec 26, 2021 | 41 894 (36.7) | 10 309 (64.1) | 0.57 | 987 (23.2) | 0.30 |
| Prior positive SARS-CoV-2 test result | 4257 (3.7) | 117 (0.7) | 0.20 | 10 (0.2) | 0.25 |
| Vaccination status | |||||
| Unvaccinated | 4681 (4.1) | 790 (4.9) | 0.04 | 1251 (29.4) | 0.72 |
| Received 2-dose primary series only with ≥1 mRNA vaccine | 91 305 (80.0) | 13 813 (85.9) | 0.16 | 2845 (66.8) | 0.30 |
| Received BNT162b2 for third dose | 14 782 (13.0) | 1225 (7.6) | 0.18 | 134 (3.1) | 0.37 |
| Received mRNA-1273 for third dose | 3319 (2.9) | 259 (1.6) | 0.09 | 31 (0.7) | 0.16 |
| Time since second dose, d | |||||
| 7-59 | 2254 (2.0) | 231 (1.4) | 0.04 | 61 (1.4) | 0.04 |
| 60-119 | 6769 (5.9) | 1003 (6.2) | 0.01 | 185 (4.3) | 0.07 |
| 120-179 | 60 722 (53.2) | 8543 (53.1) | 0 | 1855 (43.5) | 0.19 |
| 180-239 | 19 841 (17.4) | 3817 (23.7) | 0.16 | 668 (15.7) | 0.05 |
| ≥240 | 1719 (1.5) | 219 (1.4) | 0.01 | 76 (1.8) | 0.02 |
| Time since third dose, d | |||||
| 0-6 | 5963 (5.2) | 804 (5.0) | 0.01 | 74 (1.7) | 0.19 |
| 7-59 | 11 283 (9.9) | 638 (4.0) | 0.23 | 74 (1.7) | 0.35 |
| ≥60 | 855 (0.7) | 42 (0.3) | 0.07 | 17 (0.4) | 0.05 |
| Interval between first and second doses, d | |||||
| 15-34 | 15 474 (13.6) | 2273 (14.1) | 0.02 | 425 (10.0) | 0.11 |
| 35-55 | 37 972 (33.3) | 6154 (38.3) | 0.10 | 988 (23.2) | 0.23 |
| ≥56 | 55 960 (49.1) | 6870 (42.7) | 0.13 | 1597 (37.5) | 0.24 |
| Interval between second and third doses, d | |||||
| ≤111 | 232 (0.2) | 18 (0.1) | 0.02 | 8 (0.2) | 0 |
| 112-167 | 1617 (1.4) | 122 (0.8) | 0.06 | 26 (0.6) | 0.08 |
| ≥168 | 16 252 (14.2) | 1344 (8.4) | 0.19 | 131 (3.1) | 0.41 |
Participants included adults with COVID-19–relevant symptoms who were tested for SARS-CoV-2 from December 6 to 26, 2021.
Data are presented as number (percentage) of participants unless otherwise indicated.
Standardized differences greater than 0.10 were considered clinically relevant.
Comparison of Omicron-positive cases with SARS-CoV-2–negative controls.
Comparison of Delta-positive cases with SARS-CoV-2–negative controls.
Comorbidities included chronic respiratory diseases, chronic heart diseases, hypertension, diabetes, immunocompromising conditions owing to underlying diseases or therapy, autoimmune diseases, chronic kidney disease, advanced liver disease, dementia/frailty, and history of stroke or transient ischemic attack.
The sum of counts does not equal the column total because of individuals with missing information (<1.0%) for this characteristic.
Household income quintiles have variable cutoff values in each city or census area to account for cost of living. A dissemination area being in quintile 1 means it is among the lowest 20% of dissemination areas in its city by income.
Percentage of people in the area working in the following occupations: sales and service occupations; trades, transport and equipment operators, and related occupations; natural resources, agriculture, and related production occupations; and occupations in manufacturing and utilities. Census counts for people were randomly rounded up or down to the nearest number divisible by 5, which caused some minor imprecision. Quintile 1 was 0% to <32.5%; quintile 2, 32.5% to <42.3%; quintile 3, 42.3% to <50.0%; quintile 4, 50.0% to <57.5%; and quintile 5, 57.5% to 100%.
Quintile 1 was 0 to 2.1; quintile 2, 2.2 to 2.4; quintile 3, 2.5 to 2.6; quintile 4, 2.7 to 3.0; and quintile 5, 3.1 to 5.7.
Census counts were randomly rounded up or down to the nearest number divisible by 5, which caused some minor imprecision. Quintile 1 was 0.0% to 2.23%; quintile 2, 2.24% to 7.53%; quintile 3, 7.54% to 18.68%; quintile 4, 18.69% to 43.52%; and quintile 5, 43.53% to 100%.
Non-Aboriginal peoples who are not White, consisting mainly of Arab, Black, Chinese, Filipino, Korean, Japanese, Latin American, South Asian, Southeast Asian, and West Asian groups.28