Influenza virus causes an acute respiratory
infection in humans. Frequent point mutations in the
influenza genome and occasional exchange of genetic segments between virus strains help the virus evade the pre-existing immunity, resulting in epidemics and pandemics. Although vaccination is the most effective intervention, mismatches between circulating viruses and
vaccine strains reduce
vaccine efficacy. Furthermore, current
injectable vaccines induce
IgG antibodies in serum (which limit progression of
influenza symptoms) but not
secretory IgA antibodies in the respiratory mucosa (which prevent
virus infection efficiently). Therefore, numerous studies have attempted to improve
influenza vaccines. The discovery of
broadly neutralizing antibodies has progressed research into
antigen design. Studies designed to improve
vaccine efficacy by changing the
vaccine administration route have also been conducted. A thorough understanding of the mechanisms underlying the action of various
vaccines is essential if we are to develop a
universal influenza vaccine. Therefore, evaluating the quality and quantity of
antibodies induced by
vaccines, which determine
vaccine efficacy, is critical. However, at present
vaccine evaluation relies on hemagglutination inhibition tests, which only measure the quantity of antibody produced. Antibody repertoires comprise a set of
antibodies with specific genetic or molecular features that correspond to their functions. Genetically and functionally similar
antibodies may be produced by multiple individuals exposed to an identical stimulus. Therefore, it may be possible to evaluate and compare multiple
vaccine strategies in terms of the quality and quantity of an antibody response induced by a
vaccine by examining antibody repertoires. Recent studies have used single cell expression and high-throughput
immunoglobulin sequencing to provide a detailed picture of antibody responses. These novel methods may be critical for detailed characterization of antibody repertoires induced by various vaccination strategies.