The flu season of 2015-2016 saw a decrease in the effectiveness of the influenza A vaccine,
potentially caused by the introduction of new glycosylations in the hemagglutinin (HA) of H1N1.
23 seasonal influenza A virus (IAV) samples, spread across five seasons with root in the 2009
pandemic H1N1 outbreak (A(H1N1)pdm2009), are antigenically characterised by immunological
assays and sequence analysis, to determine whether glycosylation is responsible for the decrease
in vaccine effectiveness.

Similarly, characterisation with immunoblots and surface plasmon resonance (SPR) measurements
is attempted to quantify antigenic differences. Six out of eight of the surveyed IAV samples from
the 2015-2016 season have new glycosylation sites at Ser179 of HA, caused by a substitution to Asn.

Investigating resistance towards antibodies raised to A(H1N1)pdm2009 by means of hemagglutiniation
inhibition assays unveils a predominance for incremented fold-change factors in IAV samples harbouring
the Ser179!Asn substitution, as observed in IAV samples A/Denmark/30/16 and A/Denmark/46/16.
Both samples are considered to be glycosylated, which makes it a probable explanation for the decrease in
influenza A vaccine effectiveness.

Using SPR as a characterization technique of antigenic properties of IAVs requires refining. Studying analyte
type and composition is the first step in implementing this method for influenza vaccine immunology.