Past Seasons’ Vaccine Effectiveness Estimates

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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 2004-2023**

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2008-09*†	Unpublished	WI, MI, NY, TN	6,713	41	30, 50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
2022-23***	McLean 2023	WI	545	54	23, 73

*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.

***In a Wisconsin study among patients aged 6 months to 64 years, VE was 54% against medically attended outpatient acute respiratory illness (ARI) associated with laboratory-confirmed influenza A.

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

‡ Number of patients used in VE calculation.