1688. Children’s Serologic Response to H1N1 Component in Inactivated Influenza Virus (IIV) Vaccine is Dependent on Prior Season Vaccination Status
Session: Oral Abstract Session: Vaccines in the Young and Vulnerable
Friday, October 28, 2016: 2:45 PM
Room: 388-390
Background: H1N1pdm09 was the primary circulating virus in the 2015-16 influenza season in Wisconsin. To evaluate repeat vaccination effects, we assessed vaccine immunogenicity and clinical protection against H1N1pdm09 in school aged children with varying prior season vaccination patterns.

Methods: Children aged 5-17 years in Marshfield, WI were recruited in fall 2015 to provide serum before and 28 days after vaccination with inactivated influenza vaccine (IIV). Participants were assigned into strata based on prior (2014-15) season vaccination status: IIV (IIV-IIV group), live attenuated vaccine (LAIV-IIV), or unvaccinated (U-IIV). Serum samples were tested by hemagglutination inhibition (HI) against the A/California/7/2009 (H1N1)pdm09-like reference strain. Endpoints were seroconversion (defined as ≥4 fold titer rise), seroprotection (post vaccine titer ≥1:40), and mean fold rise (MFR). Illness surveillance was conducted and respiratory swabs were tested for influenza during each episode of respiratory illness.

Results: Of the 126 children in the study, 77 (61%) were in the IIV-IIV group, 13 (10%) in the LAIV-IIV group, and 36 (29%) in the U-IIV group. Pre-vaccination geometric mean titer (GMT) was 169 (95% CI 133-213) for IIV-IIV, 64 (95% CI 24-172) for LAIV-IIV, and 41 (95% CI 26-64) for U-IIV (p<0.0001). Seroprotection was 99%, 100%, and 92% for IIV-IIV, LAIV-IIV, and U-IIV, respectively (p=0.1). Percent seroconversion was 16% for IIV-IIV, 62% for LAIV-IIV, and 89% for U-IIV (p=<0.0001). U-IIV had the highest MFR (17.2, 95% CI 11.7-25.4), which was significantly higher than the mean fold rise for LAIV-IIV (8.3, 95% CI 3.9-17.8) (p=0.01) and IIV-IIV (2.0, 95% CI 1.7-2.2) (p<0.0001). MFR for LAIV-IIV was also significantly higher than IIV-IIV (p<0.0001). There were two PCR positive vaccine failures, both prior season IIV recipients, who had post-vaccination titers of 1:57 and 1:320.

Conclusion: Prior season unvaccinated individuals and LAIV recipients experienced a significantly greater antibody rise to 2015-16 IIV relative to prior season IIV recipients. However, all groups had high post-vaccination titers. There was no serologic evidence to support variation in vaccine effectiveness against H1N1pdm09 due to prior season vaccine patterns.

Jennifer King, MPH1, Huong Q. Mclean, PhD, MPH1, Brendan Flannery, PhD2, Sarah Spencer, PhD2 and Edward Belongia, MD1, (1)Center for Clinical Epidemiology and Population Health, Marshfield Clinic Research Foundation, Marshfield, WI, (2)Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA

Disclosures:

J. King, Medimmune: Investigator , Research support

H. Q. Mclean, MedImmune: Investigator , Research support

B. Flannery, None

S. Spencer, None

E. Belongia, MedImmune: Investigator , Research support
Novavax: Investigator , Research support

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