Phylogenetic trees of influenza viruses

This watercolor painting uses phylogenetic trees to depict the constant genetic changes of influenza viruses. Due to the limitations of current seasonal influenza virus vaccines, they typically elicit a strain-specific response and lose efficacy because of virus mutation in a process known as antigenic drift and shift. Scientists are developing a new generation of influenza vaccines that are able to induce antibodies with a broad protection and show high efficacy against homologous, drifted, and shifted influenza virus strains. “Antigenic drift” refers to small genetic changes, mostly in hemagglutinin (trimer, as shown in image), that lead to seasonal epidemics. It can be illustrated by the location of viruses close together on a phylogenetic tree. “Antigenic shift” indicates marked change in influenza A viruses where genomic segments are exchanged, resulting in a new influenza A subtype or a virus with a new hemagglutinin and/or neuraminidase (tetramer) combination.