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. 2016 Dec 15;63(12):1564-1573.
doi: 10.1093/cid/ciw635. Epub 2016 Oct 4.

2014-2015 Influenza Vaccine Effectiveness in the United States by Vaccine Type

Richard K Zimmerman  1 , Mary Patricia Nowalk  1 , Jessie Chung  2 , Michael L Jackson  3 , Lisa A Jackson  3 , Joshua G Petrie  4 , Arnold S Monto  4 , Huong Q McLean  5 , Edward A Belongia  5 , Manjusha Gaglani  6 , Kempapura Murthy  6 , Alicia M Fry  2 , Brendan Flannery  2 ; US Flu VE Investigators; U.S. Flu VE Investigators
Collaborators, Affiliations

2014-2015 Influenza Vaccine Effectiveness in the United States by Vaccine Type

Richard K Zimmerman et al. Clin Infect Dis. .

Abstract

Background: Circulating A/H3N2 influenza viruses drifted significantly after strain selection for the 2014-2015 vaccines. Also in 2014-2015, the Advisory Committee on Immunization Practices recommended preferential use of live attenuated influenza vaccine (LAIV) over inactivated influenza vaccine (IIV) among children aged 2-8 years.

Methods: Vaccine effectiveness (VE) across age groups and vaccine types was examined among outpatients with acute respiratory illness at 5 US sites using a test-negative design, that compared the odds of vaccination among reverse transcription polymerase chain reaction-confirmed influenza positives and negatives.

Results: Of 9311 enrollees with complete data, 7078 (76%) were influenza negative, 1840 (19.8%) were positive for influenza A (A/H3N2, n = 1817), and 395 (4.2%) were positive for influenza B (B/Yamagata, n = 340). The overall adjusted VE was 19% (95% confidence interval [CI], 10% to 27%) and was statistically significant in all age strata except those aged 18-64 years. The adjusted VE of 6% (95%CI, -5% to 17%) against A/H3N2-associated illness was not statistically significant, unlike VE for influenza B/Yamagata, which was 55% (95%CI, 43% to 65%). Among those aged 2-8 years, VE against A/H3N2 was 15% (95%CI, -16% to 38%) for IIV and -3% (CI, -50% to 29%) for LAIV; VE against B/Yamagata was 40% (95%CI, -20% to 70%) for IIV and 74% (95%CI, 25% to 91%) for LAIV.

Conclusions: The 2014-2015 influenza vaccines offered little protection against the predominant influenza A/H3N2 virus but were effective against influenza B. Preferential use of LAIV among young children was not supported.

Keywords: influenza vaccine; vaccine effectiveness.

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Figures

Figure 1.
Figure 1.
Distribution of enrollees by eligibility and vaccination status, analysis, influenza status and influenza type. Two enrollees were positive for both A/H3N2 and B.
Figure 2.
Figure 2.
Distribution of vaccine type among enrollees in 2013–2014 and 2014–2015. Abbreviations: HD, high does; IIV, inactivated influenza vaccine; IIV3, trivalent inactivated influenza vaccine; IIV4, quadrivalent inactivated influenza vaccine; LAIV, live attenuated influenza vaccine.
Figure 3.
Figure 3.
A, Adjusted vaccine effectiveness against influenza A/H3N2 by age group and vaccine type. Confidence intervals (CIs) for those aged 2–17 years: any inactivated influenza vaccine (IIV) (−9, 30); live attenuated influenza vaccine (LAIV) (−40, 20); for those aged 18–64 years: any IIV (−19, 16); standard-dose trivalent IIV (IIV3SD) (−15, 30); quadrivalent IIV (IIV4) (−23, 24); for those aged ≥65 years: any IIV (−30, 40); standard-dose trivalent IIV (IIV3SD) (−25, 54); high-dose trivalent IIV (IIV3HD) (−82, 66); IIV4 (−52, 43). B, Adjusted vaccine effectiveness against influenza B/Yamagata by age group and vaccine type. There were no cases of high-dose trivalent IIV. CIs for those aged 2–17 years: any IIV (41, 80); LAIV (43, 90); for those aged 18–64 years: any IIV (59, 20); IIV3SD (16, 64); IIV4 (−6, 65); for those aged ≥65 years: any IIV (47, 88); IIV3SD (31, 89); IIV3HD (47, 100); IIV4 (40, 92).
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