Past Seasons’ Vaccine Effectiveness Estimates

These pages include information about the seasonal flu vaccine effectiveness estimates from past seasons, including tables of the estimated vaccine effectiveness (and 95% confidence interval [CI]) by age group and virus subtype. Information on how these estimates are calculated can be found on CDC’s web page How Flu Vaccine Effectiveness and Efficacy are Measured.

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 2009

WI

762

10

-36, 40

2005-06*

Belongia 2009

WI

346

21

-52, 59

2006-07*

Belongia 2009

WI

871

52

22, 70

2007-08*

Belongia 2011

WI

1,914

37

22, 49

2008-09*†

Unpublished

WI, MI, NY, TN

6,713

41

30, 50

2009-10*

Griffin 2011

WI, MI, NY, TN

6,757

56

23, 75

2010-11*

Treanor 2011

WI, MI, NY, TN

4,757

60

53, 66

2011-12

Ohmit 2014

WI, MI, PA, TX, WA

4,771

47

36, 56

2012-13

McLean 2014

WI, MI, PA, TX, WA

6,452

49

43, 55

2013-14

Gaglani 2016

WI, MI, PA, TX, WA

5,999

52

44, 59

2014-15

Zimmerman 2016

WI, MI, PA, TX, WA

9,311

19

10, 27

2015-16

Jackson 2017

WI, MI, PA, TX, WA

6,879

48

41, 55

2016-17

Flannery 2018 WI, MI, PA, TX, WA 7,410

40

32, 46

2017-18

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

38

31, 43

2018-19

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

29

21, 35

2019-20

Tenforde 2021 WI, MI, PA, TX, WA 8,845

39

32, 44

2020-21**

n/a n/a n/a

n/a

2021-22

Price 2022 CA, MI, PA, TN, TX, WA, WI 4,312

36

21, 48

*From 2004-2005 through 2010-2011, the Flu VE Network also enrolled inpatients.

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

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

‡ Number of patients used in VE calculation.