Safety and Immunogenicity of Cell Culture-Derived A/H3N2 Variant Influenza Vaccines: A Phase I Randomized, Observer-Blind, Dose-Ranging Study

A/H3N2 variant (H3N2v) swine influenza virus containing the matrix (M) gene from the 2009 A/H1N1 pandemic virus was first identified in pigs in 2010 and subsequently detected in 12 people in the United States in 2011 [1]. The following year, 309 confirmed cases of H3N2v infection were reported across 12 states, resulting in 1 death and 16 hospitalizations [2]. The majority of cases were in children and adolescents; most cases reported agricultural fair attendance and/or contact with swine prior to illness [3]. Consequently, the US Department of Health and Human Services requested a clinical evaluation of candidate H3N2v influenza vaccines as part of their pandemic preparedness program. There were only 19 confirmed cases in 2013, suggesting restricted transmission of H3N2v virus [2, 4]. However sporadic person-to-person transmission demonstrates the epidemic potential of this emerging virus [3]. In addition, animal models have shown that H3N2v viruses have the capacity for efficient replication and transmission in mammals [5]. The aim of this Phase 1 study was to assess the safety and immunogenicity of MF59-adjuvanted and nonadjuvanted cell-culture-derived, inactivated swine origin H3N2v influenza monovalent subunit (H3N2c) vaccines in children, adolescents, adults, and the elderly, and to help identify the optimal antigen and adjuvant dose to be used in further clinical development in case the H3N2v virus threat increases. Here we present results from a planned interim analysis at Day 43; safety and antibody data from a 12-month follow-up will be presented separately.