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Background High dose (HD-IIV), standard dose (SD-IIV), and MF-59 adjuvanted (aIIV) influenza vaccines are licensed for adults ≥65 years old, but there is no preferential recommendation for a specific product. These vaccines are manufactured using egg-adapted high growth reassortant viruses. Recent data suggest that antibodies generated by egg-adapted A(H3N2) viruses may contribute to reduced vaccine effectiveness. We report results from the first year of a 2-year randomized trial of vaccine immunogenicity, including response to A(H3N2) vaccine strains propagated in egg (H3N2-egg) and cell culture (H3N2-cell). Methods Adults 65–74 years old were randomized to receive 2016–2017 trivalent inactivated influenza vaccines: SD-IIV (n = 60), HD-IIV (n = 59), and aIIV (n = 60). Pre- and post-vaccination sera were analyzed by microneutralization assays (MN) to egg- and cell-propagated A(H3N2) vaccine virus, A/Hong Kong/4801/2014 and tested by hemagglutination inhibition (HI) assays to A/California/7/2009 A(H1N1)pdm09-like and B/Brisbane/60/2008-like viruses. Endpoints were postvaccination geometric mean titer (GMT), mean fold rise (MFR), and seroconversion. Respiratory swabs from adults with acute respiratory illness during the season were tested by RT-PCR to identify vaccine failures. Results Prevaccination MN and HI titers were similar across study arms. There were no differences across study arms in postvaccination MN GMT, seroconversion, and MFR against H3N2-egg and H3N2-cell (figure). However, response was lower against H3N2-cell than H3N2-egg. HI MFR for H1N1pdm09 and B/Brisbane were significantly higher in HD-IIV than SD-IIV and aIIV recipients (figure). Eight participants had PCR-confirmed A(H3N2) infection: 1/60 (2%) SD-IIV, 4/57 (7%) HD-IIV, and 3/60 (5%) aIIV recipients. Postvaccination H3N2-cell MN GMT was 15 and 63, respectively for A(H3N2) cases and noncases. Among the eight A(H3N2) cases, postvaccination MN titers were ≥1:40 against H3N2-egg for 6 cases vs. 0 cases against H3N2-cell. Conclusion Postvaccination MN titers against H3N2 egg- and cell-propagated vaccine viruses were similar across study arms, although antibody response was lower to H3N2-cell. HD-IIV generated greater antibody response against A(H1N1)pdm09 and B compared with SD-IIV or aIIV. Disclosures All authors: No reported disclosures.

open forum infectious diseases

991. Randomized Trial of High Dose, Adjuvanted, and Standard Inactivated Influenza Vaccine Immune Response Against Egg- and Cell-Propagated Vaccine Strains in Older Adults, 2016–2017 Season