CDC Seasonal Flu Vaccine Effectiveness Studies

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CDC conducts studies each flu season to help determine how well flu vaccines are working. These vaccine effectiveness (VE) studies help regularly assess the value of flu vaccination as a public health intervention. The results of vaccine effectiveness studies can vary based on the study design, the outcome(s) measured, the population studied, and the season studied.

US Flu VE Data for 2023-2024

Past Seasons Vaccine Effectiveness Estimates

How Vaccine Effectiveness is Measured

Publications on Vaccine Benefits

On This Page

Figure 1. Effectiveness of Seasonal Flu Vaccines from the 2009-2024 Flu Seasons
Figure 2. Overall VE (pediatric and adults) by season*
Table. Adjusted vaccine effectiveness estimates for influenza seasons from 2004-2023
Supporting Research

U.S. Flu Vaccine Effectiveness Networks

CDC has been working with researchers at universities and hospitals since the 2003-2004 flu season to estimate how well flu vaccines work through observational studies using laboratory-confirmed flu as the outcome. Over the past few years, CDC has conducted VE studies using multiple vaccine effectiveness networks. More information on CDC’s vaccine effectiveness networks and studies is available at CDC’s Influenza Vaccine Effectiveness Networks.

Results from Prior Flu Seasons

The overall, adjusted vaccine effectiveness estimates for flu seasons from 2004-2024 are noted in the chart below. (Estimates are typically adjusted for study site, age, sex, underlying medical conditions, and days from illness onset to enrollment.)

Figure 1. Effectiveness of Seasonal Flu Vaccines from the 2009-2024 Flu Seasons

Download Vaccine Effectiveness PowerPoint Presentation Slides [PPT – 1 MB]

Download Excel Version [XLS – 22 KB]

The vaccine effectiveness estimates included in the chart and tables below are vaccine effectiveness estimates from the U.S. Flu VE Network.

Chart showing Seasonal Flu vaccine effectiveness.

Effectiveness of Seasonal Flu Vaccines from the 2009-2024 Flu Seasons
	2009-10	2010-11	2011-12	2012-13	2013-14	2014-15	2015-16	2016-17	2017-18	2018-19	2019-20	2020-21*	2021-22	2022-23**	2023-24^††
Adj. Overall VE (%)	56	60	47	49	52	19	48	40	38	29	39	Not enough data to compute	36	54	42

*2020-2021 flu vaccine effectiveness was not estimated due to low influenza 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 virus infection.

A point estimate is a single value that is used to estimate an unknown population parameter. Point estimates are used in statistics to make inferences about population parameters based on sample data. More information is available at How Flu Vaccine Effectiveness and Efficacy are Measured.

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Figure 2. Overall VE (pediatric and adults) by season*

Table. Adjusted vaccine effectiveness estimates for influenza seasons from 2004-2024

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
2023-2024^††****	ACIP Presentation on February 28, 2024 [1.5 MB, 37 pages]	AZ, MI, MO, PA, OH, TX, WA	3,394	42	29, 53

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

**2020-2021 flu vaccine effectiveness was not estimated due to low influenza 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 virus infection.

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

^‡Number of patients used in VE calculation.

^††VE estimates for 2022-2023 flu season are preliminary.

****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.

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Belongia EA, Kieke BA, Donahue JG, et al. Effectiveness of inactivated influenza vaccines varied substantially with antigenic match from the 2004-2005 season to the 2006-2007 season. J Infect Dis. 2009 Jan 15;199(2):159-67. doi:10.1086/595861. PubMed PMID: 19086915.

Belongia EA, Kieke BA, Donahue JG,et al. Influenza vaccine effectiveness in Wisconsin during the 2007-08 season: comparison of interim and final results. Vaccine. 2011 Sep 2;29(38):6558-63. doi: 10.1016/j.vaccine.2011.07.002. Epub 2011 Jul 19. PubMed PMID: 21767593.

Ferdinands JM, Gaglani M, Martin ET, Middleton D, Monto AS, Murthy K, Silveira FP, Talbot HK, Zimmerman R, Alyanak E, Strickland C, Spencer S, Fry AM; HAIVEN Study Investigators. Prevention of influenza hospitalization among adults in the US, 2015-16: Results from the US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN). J Infect Dis. 2018 Dec 14. doi:10.1093/infdis/jiy723. [Epub ahead of print] PubMed PMID: 30561689.external

Flannery B, Clippard J, Zimmerman RK, Norwalk MP, Jackson ML, Jackson LA, Monto AS, Petrie JG, McLean HQ, Belongia EA, Gaglani M, Berman L, Foust A, Sessions W, Thaker SN, Spencer S, Fry AM. Early Estimates of Seasonal Influenza Vaccine Effectiveness – United States, January 2015. MMWR Morb Mortal Wkly Rep. 2015 Jan 13;64(1);10-15.

Flannery 2019 Influenza Vaccine Effectiveness in the United States During the 2016-2017 Season – PubMed (nih.gov)

Flannery 2020 Spread of Antigenically Drifted Influenza A(H3N2) Viruses and Vaccine Effectiveness in the United States During the 2018-2019 Season – PubMed (nih.gov)

Gaglani 2016 Influenza Vaccine Effectiveness Against 2009 Pandemic Influenza A(H1N1) Virus Differed by Vaccine Type During 2013-2014 in the United States – PubMed (nih.gov)

Griffin MR, Monto AS, Belongia EA, et al. Effectiveness of non-adjuvanted pandemic influenza A vaccines for preventing pandemic influenza acute respiratory illness visits in 4 U.S. communities. PLoS One. 2011;6(8):e23085. doi: 10.1371/journal.pone.0023085. Epub 2011 Aug 12. PubMed PMID: 21857999.

Jackson ML, Chung JR, Jackson LA, Phillips CH, Benoit J, Monto AS, Martin ET, Belongia EA, McLean HQ, Gaglani M, Murthy K, Zimmerman R, Nowalk MP, Fry AM, Flannery B. N Engl J Med. 2017 Aug 10;377(6):534-543. doi: 10.1056/NEJMoa1700153. PMID: 2879286

McLean HQ, Thompson MG, Sundaram ME, Kieke BA, Gaglani M, Murthy K, Piedra PA, Zimmerman RK, Nowalk MP, Raviotta JM, Jackson ML, Jackson L, Ohmit SE, Petrie JG, Monto AS, Meece JK, Thaker SN, Clippard JR, Spencer SM, Fry AM, Belongia EA. Influenza Vaccine Effectiveness in the United States During 2012-2013: Variable Protection by Age and Virus Type. J Infect Dis. 2014 Nov 18. pii: jiu647. [Epub ahead of print] PubMed PMID: 25406334.

Ohmit SE, Thompson MG, Petrie JG, et al. Influenza vaccine effectiveness in the 2011-2012 season: protection against each circulating virus and the effect of prior vaccination on estimates. Clin Infect Dis. 2014 Feb;58(3):319-27. doi: 10.1093/cid/cit736. Epub 2013 Nov 13.

Rolfes 2019 Effects of Influenza Vaccination in the United States During the 2017-2018 Influenza Season – PubMed (nih.gov)

Tenforde 2020 Effect of antigenic drift on influenza vaccine effectiveness in the United States – 2019-2020 – PubMed (nih.gov)

Treanor JJ, Talbot HK, Ohmit SE, et al. Effectiveness of seasonal influenza vaccines in the United States during a season with circulation of all three vaccine strains. CID 2012; 55(7):951-959. Epub 2012 Jul 25. PubMed PMID: 22843783.

Zimmerman 20162014-2015 Influenza Vaccine Effectiveness in the United States by Vaccine Type – PubMed (nih.gov)

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