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Effectiveness of Seasonal Influenza Vaccines against Influenza A(H1N1)pdm09 Illness during Three Influenza Seasons, US Flu VE Network

Session: Oral Abstract Session: Influenza Vaccines
Thursday, October 9, 2014: 3:15 PM
Room: The Pennsylvania Convention Center: 111-AB
Background: Influenza A (H1N1)pdm09 (pH1N1) virus has circulated at different levels during each U.S. influenza season since the 2009 pandemic, with highest levels during the 2013-14 season. A pH1N1 virus (A/California/7/2009) has been included as the H1N1 component of seasonal influenza vaccines since 2010.  We investigated effectiveness of seasonal influenza vaccines against medically attended influenza illness due to pH1N1 infection over 3 seasons with varying pH1N1 virus circulation.

Methods: We analyzed data from 9665 patients with medically attended acute respiratory illnesses enrolled at five U.S. Flu VE Network study sites during the 2011-12, 2012-13 and 2013-14 influenza seasons, during periods when pH1N1 virus was identified at ≥1 study site.  Respiratory specimens from all enrollees were tested for influenza viruses using reverse transcription PCR.  Vaccination was defined as documented or reported receipt of ≥1 dose of current season influenza vaccines at least 14 days before illness onset.  Vaccine effectiveness was estimated as 100 x (1 – adjusted odds ratio) from multivariable logistic regression comparing odds of vaccination among pH1N1-positive cases versus influenza-negative patients.

Results: pH1N1 virus accounted for 112 (25%) of 440 confirmed influenza A virus cases enrolled in 2011-12, 51 (4%) of 1380 cases in 2012-13 and 742 (95%) of 778 cases in 2013-14. Over three seasons, 4401 (50%) of 8760 influenza-negative patients had received ≥1 dose of current season influenza vaccine versus 240 (27%) of 905 pH1N1 cases.  After adjusting for season, study site, age, self-reported health status and days from illness onset to enrollment, overall VE against pH1N1 virus infection during three influenza seasons was 65% (95% confidence interval [CI]: 59%, 70%), varying from 62% (95% CI: 53%, 69%) in 2013-14 to 81% (95% CI: 61%, 91%) in 2012-13, with no statistically significant difference in VE by season.  After combining seasons, adjusted age-group specific VE estimates against pH1N1 ranged from 56% (95% CI:16%, 77%) among patients 65 years to 79% (95% CI: 54%, 91%) among 9-17 year olds.

Conclusion: The pH1N1 virus included in seasonal influenza vaccines since 2009 provided consistent protection against medically-attended pH1N1 illness 2-4 years after the pandemic despite varying pH1N1 circulation.

Brendan Flannery, PhD1, Swathi Thaker, PhD1, Jessie Clippard, MPH1, Arnold Monto, MD2, Suzanne E. Ohmit, DrPH3, Richard K. Zimmerman, MD MPH4, Mary Patricia Nowalk, PhD4, Manjusha Gaglani, MBBS5, Michael Jackson, PhD, MPH6, Lisa A. Jackson, MD6, Edward Belongia, MD7, Huong Mclean, PhD, MPH7, Lashondra Berman, MSc1, Angela Foust, MS1, Wendy Sessions, MPH1, Sarah Spencer, Ph.D.1, Mark G. Thompson, PhD1 and Alicia M. Fry, MD, MPH1, (1)Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, (2)University of Michigan School of Public Health, Ann Arbor, MI, (3)Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI, (4)Family Medicine, University of Pittsburgh, Pittsburgh, PA, (5)Baylor Scott & White Health, Temple, TX, (6)Group Health Research Institute, Seattle, WA, (7)Marshfield Clinic Research Foundation, Marshfield, WI


B. Flannery, None

S. Thaker, None

J. Clippard, None

A. Monto, Sanofi Pasteur: Consultant and Grant Investigator, Consulting fee and Grant recipient
GSK: Scientific Advisor, Consulting fee

S. E. Ohmit, None

R. K. Zimmerman, Sanofi: Grant Investigator, Research grant
Pfizer: Grant Investigator, Research grant

M. P. Nowalk, Sanofi: Grant Investigator, Research support
Pfizer: Grant Investigator, Research support
Merck: Grant Investigator, Research support
MedImmune: Consultant, Consulting fee

M. Gaglani, MedImmune: Research Contractor, Research support

M. Jackson, None

L. A. Jackson, None

E. Belongia, Medimmune LLC: Grant Investigator, Grant recipient

H. Mclean, MedImmune: Collaborator, Research grant

L. Berman, None

A. Foust, None

W. Sessions, None

S. Spencer, None

M. G. Thompson, None

A. M. Fry, None

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