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J Infect Dis. 2018 Jun 20;218(2):189-196. doi: 10.1093/infdis/jix634.

Influence of Birth Cohort on Effectiveness of 2015-2016 Influenza Vaccine Against Medically Attended Illness Due to 2009 Pandemic Influenza A(H1N1) Virus in the United States.

Author information

1
Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia.
2
Kaiser Permanente Washington Health Research Institute, Seattle, Washington.
3
Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor.
4
Marshfield Clinic Research Institute, Marshfield, Wisconsin.
5
Baylor Scott and White Health, Texas A&M University Health Science Center College of Medicine, Temple.
6
University of Pittsburgh Schools of Health Sciences, Pennsylvania.
7
University of Pittsburgh Medical Center, Pennsylvania.
8
Vanderbilt University Medical Center, Nashville, Tennessee.
9
Department of Medicine, University of Rochester Medical Center, New York.

Abstract

Background:

The effectiveness of influenza vaccine during 2015-2016 was reduced in some age groups as compared to that in previous 2009 pandemic influenza A(H1N1) virus (A[H1N1]pdm09 virus)-predominant seasons. We hypothesized that the age at first exposure to specific influenza A(H1N1) viruses could influence vaccine effectiveness (VE).

Methods:

We estimated the effectiveness of influenza vaccine against polymerase chain reaction-confirmed influenza A(H1N1)pdm09-associated medically attended illness from the 2010-2011 season through the 2015-2016 season, according to patient birth cohort using data from the Influenza Vaccine Effectiveness Network. Birth cohorts were defined a priori on the basis of likely immunologic priming with groups of influenza A(H1N1) viruses that circulated during 1918-2015. VE was calculated as 100 × [1 - adjusted odds ratio] from logistic regression models comparing the odds of vaccination among influenza virus-positive versus influenza test-negative patients.

Results:

A total of 2115 A(H1N1)pdm09 virus-positive and 14 696 influenza virus-negative patients aged ≥6 months were included. VE was 61% (95% confidence interval [CI], 56%-66%) against A(H1N1)pdm09-associated illness during the 2010-2011 through 2013-2014 seasons, compared with 47% (95% CI, 36%-56%) during 2015-2016. During 2015-2016, A(H1N1)pdm09-specific VE was 22% (95% CI, -7%-43%) among adults born during 1958-1979 versus 61% (95% CI, 54%-66%) for all other birth cohorts combined.

Conclusion:

Findings suggest an association between reduced VE against influenza A(H1N1)pdm09-related illness during 2015-2016 and early exposure to specific influenza A(H1N1) viruses.

PMID:
29361005
PMCID:
PMC6009604
[Available on 2019-06-20]
DOI:
10.1093/infdis/jix634

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