Table 1. Characteristics of the Adolescents.
| Characteristic | Participants, No. (%) | Standardized mean differencea | ||
|---|---|---|---|---|
| Total (N = 542) | Case (n = 186) | Control (n = 356) | ||
| Age, median (IQR), y | 14 (13-16) | 14 (13-16) | 14 (13-16) | −0.09 |
| Sex | ||||
| Female | 262 (48.3) | 86 (46.2) | 176 (49.4) | −0.06 |
| Male | 280 (51.7) | 100 (53.8) | 180 (50.6) | 0.06 |
| Race or ethnic group | ||||
| Black, non-Hispanic | 81 (14.9) | 34 (18.3) | 47 (13.2) | 0.14 |
| Hispanic or Latinx | 82 (15.1) | 37 (19.9) | 45 (12.6) | 0.20 |
| White, non-Hispanic | 297 (54.8) | 92 (49.5) | 205 (57.6) | −0.16 |
| Otherb | 66 (12.2) | 14 (7.5) | 52 (14.6) | −0.23 |
| Unknown | 16 (3.0) | 9 (4.8) | 7 (2.0) | 0.16 |
| Health insurance | ||||
| Private | 311 (57.4) | 88 (47.3) | 223 (62.6) | −0.31 |
| Government | 166 (30.6) | 67 (36.0) | 99 (27.8) | 0.18 |
| Uninsured or unknown | 65 (12.0) | 31 (16.7) | 34 (9.6) | 0.21 |
| Medical history | ||||
| Any comorbiditiesc | 190 (35.1) | 63 (33.9) | 127 (35.7) | −0.04 |
| BMI >95 percentile | 80 (14.8) | 30 (16.1) | 50 (14.0) | 0.06 |
| Month sample was obtained | ||||
| June | 68 (12.5) | 24 (12.9) | 44 (12.4) | 0.02 |
| July | 192 (35.4) | 64 (34.4) | 128 (36.0) | −0.03 |
| August | 282 (52.0) | 98 (52.7) | 184 (51.7) | 0.02 |
| BNT162b2 vaccination status | ||||
| Unvaccinated | 388 (71.6) | 173 (93.0) | 215 (60.4) | 0.83 |
| 1 Dose | 20 (3.7) | 3 (1.6) | 17 (4.8) | −0.18 |
| 2 Doses | 134 (24.7) | 10 (5.4) | 124 (34.8) | −0.79 |
| Health care utilization | ||||
| ≥1 Influenza vaccine dosed | 132 (24.4) | 45 (24.2) | 87 (24.4) | −0.03 |
| Medical visits after Jan 1, 2020, median (range) | 3.0 (1.0 to 5.0) | 2.0 (0.0 to 4.0) | 3.0 (1.0 to 6.0) | −0.14 |
Abbreviation: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared).
a
The standardized mean difference is the difference in means between case and control participants in units of the pooled SD. Covariates with a standardized mean difference greater than 0.2 were considered to have important imbalances.
b
Race or ethnic group was determined from electronic health records. Other race included American Indian or Alaska Native, Asian, Native Hawaiian, Pacific Islander, and multiracial.
c
Table 2 presents more details on comorbidities.
d
One dose of influenza vaccine after August 1, 2020.