Past Seasons' Vaccine Effectiveness Estimates

What to know

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.

Past Seasons' Estimates

Table. Adjusted vaccine effectiveness estimates for influenza seasons from 2004–2005 to 2025–2026

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Unpublished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

 n/a

2021–22

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

36

 21, 48

2022–23

 Chung 2024 MI, PA, TX, WA, AZ, MO, OH 2,561 30 -9, 54

2023–24***

 Chung 2025 AZ, MI, MO, PA, OH, TX, WA 9,061 44 36, 51

2024–25††

 Frutos 2025 MN, WI, UT, CA, OR, WA, IN, CO 139,558 56 54, 58

2025–26††

 Maloney 2026 MN, WI, UT, CA, OR, WA, IN, CO 135,422 36 33, 39

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

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

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

‡Number of patients used in VE calculation.

CIs that exclude 0 are considered to be statistically significant.

***Overall VE was calculated for this table to be consistent with what has been reported historically and is available for comparison with historical estimates. All other 2023–2024 VE estimates are reported by age group.

††VE estimates for 2024–2025 and 2025–2026 flu seasons are preliminary.

Information on how these estimates are calculated can be found on CDC's web page How Flu Vaccine Effectiveness and Efficacy are Measured.

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Content Source:
National Center for Immunization and Respiratory Diseases (NCIRD)