[8][9] Influenza viruses C and D were estimated to have diverged from a common ancestor over 1,500 years ago, around 482 AD.

[4][11][8] Influenza C virus is not as easily isolated so less information is known of this type, but studies show that it occurs worldwide.

[8]Metatranscriptomics studies also have identified closely related "Influenza C and D-like" viruses in several amphibian and fish species suggesting the potential for divergent influenza C/D like viruses circulating in aquatic systems.

[4] Influenza viruses have a relatively short incubation period (lapse of time from exposure to pathogen to the appearance of symptoms) of 18–72 hours and infect the epithelial cells of the respiratory tract.

[15] Cold-like symptoms are associated with the virus including fever (38–40 °C), dry cough, rhinorrhea (nasal discharge), headache, muscle pain, and achiness.

[4] Most children between five and ten years old have already produced antibodies for influenza virus C.[16] As with all influenza viruses, type C affects individuals of all ages but is most severe in young children, the elderly and individuals with underlying health problems.

[4][17] Young children have less prior exposure and have not developed the antibodies and the elderly have less effective immune systems.

Fusion of these membranes allows the viral proteins and genome to be released into the host cell, which then causes the infection.

When either of these processes occur, the antibodies formed by the immune system no longer protect against these altered glycoproteins.

[11] Influenza viruses A and B also cause seasonal epidemics almost every year due to their ability to antigenic drift.