Waning of antibodies against influenza virus after vaccination or infection

Abstract

Waning of antibodies against influenza virus after vaccination or infection Nancy H. L. Leung, Ranawaka A. P. M. Perera, Vicky J. Fang, Dennis K. M. Ip, J. S. Malik Peiris, Benjamin J. Cowling WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, The University of Hong Kong (all authors) The immunogenicity of eliciting serum antibodies measured by haemagglutination inhibition (HAI) assay is used as a proxy for vaccine effectiveness (VE) of inactivated influenza vaccines (IIV). Decreasing VE has been observed in all age groups over the course of an influenza season, and the waning of antibody over time after vaccination has been suggested to contribute to the decline in influenza vaccine effectiveness. To study waning in HAI antibody titers after vaccination and natural infection, 796 children were recruited and randomized to receive IIV or placebo at enrollment in 2009-10, and together with their family members they were followed up longitudinally for subsequent years until 2015. Vaccination status in years 2010-15 was self-reported before each winter influenza season. Laboratory-confirmed influenza virus infection was identified by PCR from respiratory specimens collected during active surveillance efforts throughout the year including daily symptom diary, weekly phone calls or self-report to study hotline. HAI titers were determined from paired sera collected before and after each winter influenza season. Waning in HAI titer over time for different influenza subtypes in individuals during an influenza epidemic after vaccination or natural infection was identified by imputing intermediate unobserved titers between the measured titers before and after the influenza epidemic using log-linear regression models with linear and quadratic terms for calendar time. We estimated the average time for two-fold drop in HAI titer was approximately 6 months. This may suggest more frequent influenza vaccination may be considered in regions with extended periods of influenza activities throughout the year.