Table 1.
Background characteristics of the study cohort.
| Variables | Number of cases | Subcategory | Total | Pre-Delta VOC era | Delta VOC era | P value |
|---|---|---|---|---|---|---|
| Case number | 1299 | 1299 | 950 | 349 | ||
| Age (years), median (IQR) | 1299 | 9.0 (3.0–14.0) | 10.0 (4.0–15.0) | 7.0 (2.0–13.0) | <0.001 | |
| Age category, number (%) | 1299 | 0 to <3 month | 25 (1.9) | 11 (1.2) | 14 (4.0) | <0.001 |
| 3 to <24 month | 202 (15.6) | 140 (14.7) | 62 (17.8) | |||
| 2 to <6 years | 228 (17.6) | 156 (16.4) | 72 (20.6) | |||
| 6 to <13 years | 382 (29.4) | 280 (29.5) | 102 (29.2) | |||
| ≥13 years | 462 (35.6) | 363 (38.2) | 99 (28.4) | |||
| Male sex, number (%) | 1299 | Male | 720 (55.4) | 529 (55.7) | 191 (54.7) | 0.801 |
| Body mass index, median (IQR) | 1051 | 18.1 (16.0–20.8) | 18.4 (16.0–20.8) | 17.7 (15.9–20.4) | 0.090 | |
| Underlying disease*, number (%) | 1299 | Any underlying disease | 114 (8.8) | 70 (7.4) | 44 (12.6) | 0.004 |
| Bronchial asthma | 58 (4.5) | 39 (4.1) | 19 (5.4) | 0.292 | ||
| Obesity | 17 (1.3) | 9 (0.9) | 8 (2.3) | 0.093 | ||
| Congenital heart anomaly | 16 (1.2) | 11 (1.2) | 5 (1.4) | 0.777 | ||
| Congenital anomaly or chromosomal abnormality | 8 (0.6) | 6 (0.6) | 2 (0.6) | 1.0 | ||
| Diabetes without complication | 7 (0.5) | 4 (0.4) | 3 (0.9) | 0.394 | ||
| Hypertension | 5 (0.4) | 3 (0.3) | 2 (0.6) | 0.615 | ||
| Others# | 16 (1.2) | 9 (0.9) | 7 (2.0) | 0.154 | ||
| Immunosuppressive condition, number (%) | 1299 | 8 (0.6) | 5 (0.5) | 3 (0.9) | 0.450 | |
| Exposure within 14 days prior to admission | 1280 | Travel abroad | 10 (0.8) | 10 (1.1) | 0 (0.0) | 0.004 |
| 1284 | Close contact with COVID-19 cases | 1069 (83.3) | 783 (83.6) | 286 (82.4) | 0.202 | |
| 1299 | Family | 826 (63.6) | 597 (62.8) | 229 (65.6) | 0.363 | |
| Educational facility | 181 (13.9) | 141 (14.8) | 40 (11.5) | 0.125 | ||
| Nonfamily roommates | 15 (1.2) | 13 (1.4) | 2 (0.6) | 0.379 | ||
| Workplace | 7 (0.5) | 6 (0.6) | 1 (0.3) | 0.682 | ||
| Healthcare facility | 5 (0.4) | 3 (0.3) | 2 (0.6) | 0.615 | ||
| Others | 51 (3.9) | 37 (3.9) | 14 (4.0) | 0.874 | ||
| Days of hospitalization from symptom onset, median (IQR) | 1011 | 3.0 (1.0–4.0) | 3.0 (1.0–5.0) | 3.0 (1.0–4.0) | 0.981 | |
| Number of SARS-CoV-2-vaccinated patients | 349 | 4 (1.1) | 0 (NA) | 4 (1.1) | 1.0 | |
| Number of asymptomatic patients | 1299 | 281 (21.6) | 245 (25.8) | 36 (10.3) | <0.001 |
SARS-CoV-2, severe acute respiratory coronavirus type 2; VOC, variant of concern; IQR, interquartile range; NA, not applicable.