LB12. A Randomized Controlled Trial of Antibody Response to 2018–2019 Cell-based vs. Egg-based Quadrivalent Inactivated Influenza Vaccine in Children

BACKGROUND: While vaccine effectiveness varies across seasons and age groups, influenza vaccination is still the most effective means of preventing influenza infection. Current vaccine effectiveness improvement efforts are focused on manufacturing methods whereby the use of eggs as a growth medium is being minimized to prevent egg adaptation mutations that render the vaccine less effective. This study compared children’s immune response to two FDA-approved influenza vaccines, cell-based vs. egg-based, in an unblinded randomized controlled trial. METHODS: Racially diverse, healthy children ages 4–20 years were randomly assigned 1:1 in blocks of 4 to receiveeither quadrivalent inactivated cell-based or egg-based influenza vaccine. Blood was drawn at Day 0 before vaccination and at Day 28 post vaccination (range = 19–35 days) and analyzed for hemagglutination inhibition (HAI) titers using standard protocols against egg-grown vaccine antigens. Primary outcome measures were seropositivity, defined as HAI titer ≥1:110 and ≥1:40; seroconversion, defined as the HAI titer ratio of Day 28/Day 0 ≥4 and HAI titer at Day 28 ≥40; and fold-rise, defined as antilog of average log(2)HAI titer ratio of Day 28/Day 0. Secondary outcomes were compared for those vaccinated and not vaccinated the previous year. RESULTS: Baseline demographics including age, sex, race, ethnicity, parental educational status, health insurance coverage, and exposure to household smoking did not differ between vaccine groups. There were no differences in any HAI antibody response between the two vaccine groups (table). Participants unvaccinated in the prior season (2017–2018, N = 62) were more likely than those vaccinated (N = 86) to seroconvert to any strain in 2018–2019 (≥1 strain seroconverted: 68% unvaccinated vs. 35% vaccinated in 2017–2018, P < 0.001). Day 28 titer fold-rise difference was 2.0 for A/H1N1, 0.65 for A/H3N2, 1.1 for B/Colorado and 0.9 for B/Phuket. CONCLUSION: There were no differences for any HAI antibody titer outcome between children receiving the two vaccines. Overall, the cohort had HAI titers at levels sufficient to be considered seropositive at baseline. Those unvaccinated in the preceding season had higher seroconversion rates than those vaccinated in both seasons. [Image: see text] DISCLOSURES: Patricia Nowalk, PhD, Merck & Co. (Grant/Research Support); others, no reported disclosures .