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533
Persistence of Antibody to Influenza Hemagglutinin over Two Influenza Seasons

Session: Oral Abstract Session: Influenza Vaccines
Thursday, October 9, 2014: 2:45 PM
Room: The Pennsylvania Convention Center: 111-AB
Background: Antibody to influenza hemagglutinin (HA) is a correlate of influenza immunity. Anti-HA antibody levels increase after infection or vaccination and then decline over time. It has been suggested that this can result in waning of vaccine effectiveness over a single influenza season. However, evidence is mixed regarding the rate of antibody decline with most studies reporting only the proportion of subjects meeting vaccine licensure criteria over time.   

Methods: Healthy subjects ages 18 to 49 years were enrolled in a double-blind trial and randomized to receive inactivated (IIV) or live-attenuated (LAIV) influenza vaccine or placebo. Subjects were followed over two influenza seasons (October 2005 - May 2007) without re-vaccination in the second. Serologic specimens were collected at 5 time points over follow-up. Hemagglutination inhibition (HAI) assays were performed on serologic specimens to determine HAI titers to the influenza A (H3N2) and B strains included in the 2005-06 vaccine. Rates of antibody decline among 941 subjects without evidence of influenza infection were estimated in linear models with mean log2 HAI titer as the outcome and time from intervention as the exposure. 

Results: IIV recipients achieved higher mean log2 HAI titers one month post-intervention than LAIV or placebo recipients (P<0.001). IIV recipients also experienced the highest rates of antibody decline; however, this appears to be driven by an association with higher peak antibody levels rather than a specific intervention effect. Despite higher rates of decline, IIV recipients maintained higher titers than LAIV or placebo recipients after 18 months (P<0.001). IIV recipients known to have been vaccinated in the 2004-05 season had higher titers prior to 2005-06 vaccination (P<0.001), but lower titers for the entire post-vaccination period than those not known to have been previously vaccinated (P<0.001). 

Conclusion: Moderate HAI titer decreases were observed over 18 months, suggesting a slower rate of decline than previously thought. The rate of decline increases as peak post-vaccination titer increases. Subjects vaccinated two years in a row exhibited decreased vaccine response in the second year. The impact of the persistence of HA antibody, and other immune correlates, on vaccine efficacy requires further study.

Joshua G. Petrie, MPH, Suzanne E. Ohmit, DrPH, Rachel Cross, MPH and Arnold Monto, MD, Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI

Disclosures:

J. G. Petrie, None

S. E. Ohmit, None

R. Cross, None

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

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