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

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.

Repeated annual influenza vaccination and vaccine effectiveness: review of evidence

“…However, this difference was not observed in the 2014-2015 U.S. Flu VE Network Study which had more influenza cases with repeated vaccination and single season vaccination than the other two studies combined [13].…”

“…Eighteen studies met the eligibility criteria [4,13,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. Of these, one study was restricted to hospitalized patients and was therefore excluded from the meta-analysis [31].…”

“…We included one publication after 3 August 2016 because results were available to us before online publication on 4 October 2016 [13]. The specific search terms are shown in the online appendix, and the protocol is available from the authors on request.…”

The beneficial effects of vaccination on the evolution of seasonal influenza

“…As influenza evolves from year to year, antigenic differences between previously and currently circulating strains contribute to low vaccine efficacy [1][2][3][4] and high incidence of influenza illness [2,5]. While vaccines regularly undergo reformulation to address this mismatch, vaccines may also affect antigenic evolution.…”

Are children's vitamin D levels and BMI associated with antibody titers produced in response to 2014–2015 influenza vaccine?

“…Specifically, in 2014-2015, LAIV effectiveness against A(H3N2) virus was 11% (95%CI D -1, 21) and against B virus (Yamagata lineage) was 54% (95% CI D 41, 64). 35 In our serology data, to the extent that LAIV was eliciting an immune response (i.e., B lineages), it was significantly and inversely associated with vitamin D levels. Small sample size among the IIV recipients may have masked a similar response to this form of the vaccine.…”