The virion shape can be spherical, elliptical, or even filamentous with a length of tens of micrometers<ref name="Arti13">Native Morphology of Influenza Virions, Frontiers in microbiology, 2011, Noda T., https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249889/</ref>. The virion is made up of a viral envelope containing two main types of proteins, wrapped around a central core.