Past Seasons Vaccine Effectiveness Estimates

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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 2004-2021

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

Table. Adjusted vaccine effectiveness estimates for influenza seasons from 2004-2021 18CDC calculates vaccine effectiveness estimates through the U.S. VE Network
Influenza Season^†	Reference	Study Site(s)	No. of Patients^‡	Adjusted Overall VE (%)	95% CI
2020-2021**
2019-20	Flannery, 2020external icon	WI, MI, PA, TX, WA	8,845	39	32, 44
2018-19	Flannery 2020external icon	WI, MI, PA, TX, WA	3,254	29	21, 35
2017-18	Rolfes 2019external icon	WI, MI, PA, TX, WA	8,436	38	31, 43
2016-17	Flannery 2019external icon	WI, MI, PA, TX, WA	7410	40	32, 46
2015-16	Jackson 2017external icon	WI, MI, PA, TX, WA	6879	48	41, 55
2014-15	Zimmerman 2016external icon	WI, MI, PA, TX, WA	9311	19	10, 27
2013-14	Gaglani 2016external icon	WI, MI, PA, TX, WA	5999	52	44, 59
2012-13	McLean 2014external icon	WI, MI, PA, TX, WA	6452	49	43, 55
2011-12	Ohmit 2014external icon	WI, MI, PA, TX, WA	4771	47	36, 56
2010-11	Treanor 2011external icon	WI, MI, NY, TN	4757	60	53, 66
2009-10	Griffin 2011external icon	WI, MI, NY, TN	6757	56	23, 75
2008-09	Unpublished	WI, MI, NY, TN	6713	41	30, 50
2007-08	Belongia 2011external icon	WI	1914	37	22, 49
2006-07	Belongia 2009external icon	WI	871	52	22, 70
2005-06	Belongia 2009external icon	WI	346	21	-52, 59
2004-05	Belongia 2009external icon	WI	762	10	-36, 40

**2020-2021 influenza vaccine effectiveness was not estimated due to low influenza virus circulation during the 2020-2021 influenza season.
* Vaccine effectiveness estimates for 2019-2020 are preliminary estimates and will be updated with final estimates at the end of the 2019-2020 U.S. influenza season.
* From 2004-05 through 2010-11, the Network also enrolled inpatients.
† Vaccine effectiveness (VE) estimates for the 2008-2009 flu season have not yet been published.
‡ Number of patients used in VE calculation.

Page last reviewed: August 26, 2021

Content source: Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)