Table 2 Characteristics of participants in the severe and general H1N1 subgroups of the post-COVID-19 group

Age (y), median (IQR)

4.0 (2.3, 5.9)

5.5 (4.1, 6.6)

< 0.001

Male, n (%)

66 (71.0)

184 (54.4)

0.004

BMI (kg/m2), median (IQR)

19.4 (18.1, 21.1)

17.5 (16.3, 19.1)

< 0.001

Vaccination status, n (%)

 H1N1 vaccination

4 (4.3)

12 (3.6)

0.735

 COVID-19 vaccination

85 (91.4)

315 (93.2)

0.552

  One-dose vaccination

21 (22.6)

68 (20.1)

0.603

  Two-dose vaccination

48 (51.6)

153 (45.3)

0.277

  Three-dose vaccination

16 (17.2)

94 (27.8)

0.038

Symptoms, n (%)

 Fever

93 (100.0)

327 (96.7)

0.078

  Duration of fever (d), median (IQR)

6.0 (5.0, 8.0)

4.0 (3.0, 5.0)

< 0.001

  Fever peak (°C), median (IQR)

39.1 (38.8, 39.6)

39.0 (38.7, 39.4)

0.022

 Cough

88 (94.6)

307 (90.8)

0.241

 Rhinorrhea

36 (38.7)

121 (35.8)

0.605

 Wheezing

52 (55.9)

79 (23.4)

< 0.001

 Sore throat

19 (20.4)

64 (18.9)

0.746

 Headache

12 (12.9)

37 (10.9)

0.599

 Myalgia

17 (18.3)

88 (26.0)

0.123

 Seizures

41 (44.1)

37 (10.9)

< 0.001

 Drowsiness

65 (69.9)

85 (25.1)

< 0.001

 Diarrhea

15 (16.1)

34 (10.1)

0.102

 Vomiting

18 (19.4)

44 (13.0)

0.123

 Abdominal pain

10 (10.8)

22 (6.5)

0.167

Laboratory findings, median (IQR)

 Leukocyte count (×10⁹/L)

9.5 (6.9, 12.4)

5.7 (4.1, 7.4)

< 0.001

 Neutrophil proportion (%)

56.1 (45.9, 68.2)

44.5 (29.3, 57.4)

< 0.001

 Lymphocyte proportion (%)

28.8 (15.3, 42.2)

44.0 (30.9, 59.7)

< 0.001

  Proportion of CD3⁺T cells (%)

58.5 (47.4, 66.8)

70.6 (67.4, 74.2)

< 0.001

  Proportion of CD3⁺8⁺T cells (%)

22.3 (16.7, 26.6)

26.9 (22.8, 32.1)

< 0.001

  Proportion of CD3⁺4⁺T cells (%)

28.7 (23.3, 34.6)

37.7 (31.6, 43.5)

< 0.001

  Proportion of NK cells (%)

13.2 (9.3, 19.7)

12.6 (9.1, 16.2)

0.199

  Proportion of B cells (%)

19.3 (14.0, 29.5)

18.8 (15.8, 21.6)

0.086

 CRP (mg/L)

23.5 (23.1, 25.1)

14.6 (10.1, 17.0)

< 0.001

 IL-6 (pg/mL)

28.7 (19.5, 48.9)

19.3 (16.6, 28.4)

< 0.001

 IL-10 (pg/mL)

23.7 (17.6, 29.0)

14.9 (12.0, 19.6)

< 0.001

 TNF-α (pg/mL)

13.2 (9.5, 18.8)

7.3 (4.5, 12.7)

< 0.001

 CK-MB (U/L)

53.2 (43.9, 74.4)

43.9 (39.5, 50.0)

< 0.001

 hs-TnT (pg/mL)

7.8 (4.2, 13.2)

4.1 (2.6, 5.8)

< 0.001

 ALT (U/L)

17.0 (13.0, 25.5)

15.0 (12.0, 21.3)

0.065

 AST (U/L)

33.0 (26.0, 41.5)

32.0 (23.0, 41.0)

0.478

 Fibrinogen (g/L)

4.1 (3.7, 4.9)

3.8 (3.4, 4.6)

0.002

Co-infection with SARS-CoV-2, n (%)

18 (19.4)

37 (10.9)

0.031

Mechanical ventilation, n (%)

20 (21.5)

0 (0.0)

< 0.001

LOS (d), median (IQR)

9.0 (8.0, 11.0)

7.0 (6.0, 8.0)

< 0.001