Table 1 Epidemiological data of the influenza virus from 2009 to 2019 in Belgium

Length (weeks)

33

12

6

12

6

10

10

7

12

8

9.3 (11.7)

2.7 (7.9)

 Period (week/year)

40/2009; 20/2010

50/2010; 9/2011

6/2012;

11/2012

1/2013; 12/2013

6/2014; 11/2014

4/2015; 13/2015

4/2016; 13/2016

2/2017; 9/2017

2/2018; 13/2018

4/2019; 11/2019

8.8/11.3^a

15.6/1.6^a

11.9/12.2*^a

12.2/3.1*^a

Intensity (Low-Moderate-High)

M

M

M

H

L

H

M

M

M

M

M

/

Intensity (maximum #GP consultations/100.000 citizens)

–800

500

531

1100

311

1036

775

787

744

761

727.2

251.2

734.5*

238*

Intensity (week/year of maximum #GP consultations)

44/2009

1/2011

7/2012

6/2013

9/2014

6/2015

9/2016

5/2017

10/2018

7/2019

6.7

2.7

10.4*

12.1*

ILI-Surveillance: positive samples (%)

37.2

48.8

42.6

59

34.5

51.9

51.6

51.5

59

52.7

51.1

7.6

49.6*

8.5*

 Positive influenza A samples (%)

99.5

55.4

93.4

44.4

98.2

83.7

48.8

99.7

34.6

99.2

70.5

27.5

73.7*

27.5*

  A(H3N2) (%)

2

96

20.2

58.6

80.2

1.1

97.3

25.4

72.5

50.4

38.8

  A(H1N1)pdm09 (%)

54

98

0.09

75

38.6

14.8

93

0.9

69.4

23.6

45.9

38.7

46.7*

36.6*

 Positive influenza B samples (%)

0.05

44.6

6.6

55.3

1.6

16.3

51.7

0.3

65.4

0.8

27

26.9

24.3*

26.7*

  B/Yamagata (%)

7

80

95.4

50

92.4

3

100

92.9

0

57.8

43.4

  B/Victoria (%)

93

12

4.1

25

7.6

96.4

0

3.2

100

37.9

44.5

 First positive samples (week/year)

28/2009

/

46/2011

45/2012

46/2013

40/2014

42/2015

47/2016

47/2017

48/2018

45.2^a

2.6^a

43.5*^a

6*^a

 Increased positive samples (week/year)

34/2009

48/2010

3/2012

52/2012

4/2014

50/2014

53/2015

53/2016

52/2017

52/2018

40.8^a

21.2^a

40.1*^a

20.1*^a

 Positivity rate (week:%)

/

3:73

7:73

5:85

10:60

5:74

10:80

5:74

7:88.7

10:82

6.9:76.6

2.6:8.5

Sari-surveillance: positive samples (%)

/

18.7

31.3

43.1

30.7

46.2

46

39.6

41.5

29.7

36.3

9.3

 Positive influenza A samples (%)

/

61.5

98

52.7

99.3

88.3

62.4

98.8

39.1

99.7

77.7

23.8

  A(H3N2) (%)

/

2

94

29.5

60.2

82.7

1

94.6

27.6

79.9

52.4

38.1

  A(H1N1)pdm09 (%)

/

98

0

66

31

11.5

90.5

0.4

67.8

18.1

42.6

38.4

 Positive influenza B samples (%)

/

38.5

2

47.1

0.6

11.7

36.8

1.2

60.9

0.3

22.2

23.7

  B/Yamagata (%)

/

12.9

100

93

100

92.4

1.1

71.4

96.5

50

68.4

38.5

  B/Victoria (%)

/

87.1

0

2.5

0

6.4

97.8

28.6

1.3

50

29.7

39.6

 Hospitalisation: LOS (days)

/

/

9.1

8.7

7.7

9.4

6.8

8.6

8.8

8.4

0.9

  Complications (%)

/

/

16

13^b–15^c

15

14.1

11.6

14^b

11.3^b

13^b

13.6

1.7

  Deaths (%)

/

/

8.6

4

5.7

6.7

5

6

5.6

6.4

6

1.3

  Patients receiving antiviral treatment (%)

6.3^d

/

8

15

5

3

3

/

/

/

6.8

5

  Seasonal Influenza virus

A(H1N1)pdm09

A(H1N1)pdm09 & B/Vic

A(H3N2)

A(H1N1)

pdm09 & B/Yam

A(H3N2)& A(H1N1)

pdm09

A(H3N2) & B/Yam

A(H1N1)

pdm09 & B/Vic

A(H3N2)

B/Yam & A(H1N1)

pdm09

A(H3N2)& A(H1N1) pdm09