Past Seasons Vaccine Effectiveness Estimates

These pages include information about the estimated seasonal influenza vaccine effectiveness from past seasons, including tables of the estimated vaccine effectiveness (and 95% credible interval [Cr I]) by age group and virus subtype. Information on how these estimates are calculated can be found on CDC’s web page How CDC Estimates vaccine efficacy and effectiveness.

Table. Adjusted vaccine effectiveness estimates for influenza seasons from 2004-2022

CDC calculates vaccine effectiveness estimates through the U.S. VE Network

Table. Adjusted vaccine effectiveness estimates for influenza seasons from 2004-2018CDC calculates vaccine effectiveness estimates through the U.S. VE Network

Influenza Season

Reference

Study Site(s)

No. of Patients

Adjusted Overall VE (%)

95% CI

2004-05**

Belongia 2009external icon

WI

762

10

-36, 40

2005-06**

Belongia 2009external icon

WI

346

21

-52, 59

2006-07**

Belongia 2009external icon

WI

871

52

22, 70

2007-08**

Belongia 2011external icon

WI

1914

37

22, 49

2008-09**†

Unpublished

WI, MI, NY, TN

6713

41

30, 50

2009-10**

Griffin 2011external icon

WI, MI, NY, TN

6757

56

23, 75

2010-11**

Treanor 2011external icon

WI, MI, NY, TN

4757

60

53, 66

2011-12

Ohmit 2014external icon

WI, MI, PA, TX, WA

4771

47

36, 56

2012-13

McLean 2014external icon

WI, MI, PA, TX, WA

6452

49

43, 55

2013-14

Gaglani 2016external icon

WI, MI, PA, TX, WA

5999

52

44, 59

2014-15

Zimmerman 2016external icon

WI, MI, PA, TX, WA

9311

19

10, 27

2015-16

Jackson 2017external icon

WI, MI, PA, TX, WA

6879

48

41, 55

2016-17

Flannery 2018external icon WI, MI, PA, TX, WA 7410

40

32, 46

2017-18

Rolfes 2019external icon WI, MI, PA, TX, WA 8,436

38

31, 43

2018-19

Flannery 2019external icon WI, MI, PA, TX, WA 10,041

29

21, 35

2019-20

Flannery, 2020external icon WI, MI, PA, TX, WA 8,845

39

32, 44

2020-21*

n/a n/a n/a

n/a

2021-22***

Chung, 2022 CA, MI, PA, TN, TX, WA, WI 3.636

14

-17, 37

* 2020-2021 flu vaccine effectiveness was not estimated due to low flu virus circulation during the 2020-2021 flu season.

** From 2004-05 through 2010-11, the Flu VE Network also enrolled inpatients.

***Interim VE estimates

† Vaccine effectiveness (VE) estimates for the 2008-2009 flu season have not been published.

‡ Number of patients used in VE calculation.