2739. Comparison of Hemagglutination Antibody Inhibition (HAI) Titers Following Influenza Vaccination by Birth Cohort and Repeated Influenza Vaccination History

BACKGROUND: The host immune response to influenza vaccination can be affected by prior imprinting to a specific influenza strain based on birth cohort and prior influenza vaccination history. Understanding the underlying immune mechanisms is essential to development of an improved seasonal vaccine and an effective universal influenza vaccine. METHODS: This is a prospective pilot study, with a total of 20 subjects in either the H3N2 cohort (N = 10, born 1968–1977) or the H1N1 cohort (N = 10, born 1948–1957). Each cohort was further stratified by subjects who have received the influenza vaccine < 2 or ≥ 3 of the past 5 years. The FDA-approved quadrivalent 2018–19 influenza vaccine (containing A(H1N1), an A/Michigan/45/2015-like virus; A(H3N2), an A/Singapore/INFIMH-16–0019/2016-like virus; B/Colorado/06/2017-like virus; and B/Phuket/3073/2013-like virus) was administered on Day 1. Demographic information included age, gender, ethnicity, and BMI. HAI titers for each component of the vaccine were obtained at baseline, 29 days post-vaccination, and 180 days post-vaccination. HAI fold-change and HAI geometric mean titers (GMT) were analyzed. RESULTS: There was no significant difference between H1N1 or H3N2 HAI fold-change in the H3N2 birth cohort (P = 0.7496) or in the H1N1 birth cohort (P = 0.8237), Figure A. Comparing HAI fold-change for the repeatedly vs. minimally vaccinated groups, there was a significant higher fold change in the minimally vaccinated group (H1N1 HAI (P = 0.002) and H3N2 HAI (P < 0.0001), Figure B). GMT was higher at baseline for the repeatedly vaccinated group (H1N1, 70; H3N2, 98; vs. H1N1, 30; H3N2, 21 for the minimally vaccinated group); however, the GMT for the minimally vaccinated group was higher at day 29 (H1N1, 172; H3N2, 184; vs. H1N1, 422; H3N2, 299 for the minimally vaccinated group; Figure C). HAI titers and analysis at day 180 post vaccination are in progress. CONCLUSION: There was no evidence of an imprinting effect by birth cohort for HAI titer magnitudes, even when stratified by vaccination history. There was a significantly higher HAI fold change for individuals who had received minimal influenza vaccinations in the past 5 years at 29 days post-vaccination. Individuals who had repeated vaccinations in the last 5 years had higher HAI GMT at baseline. DISCLOSURES: Nadine Rouphael, MD, Merck: I conduct as Emory PI the PNEUMO MERCK study at Emory, Research Grant; Pfizer: I conduct as co-PI the RSV PFIZER study at Emory, Research Grant; Sanofi-Pasteur: I conducted as Emory PI the CDIFFENSE trial at Emory, Research Grant.