The primary mode of transmission of the influenza virus is through respiratory droplets expelled when an infected person coughs, sneezes, or talks. These droplets can directly enter the respiratory tract of a nearby person or contaminate surfaces that others touch, leading to infection when they touch their face. This mode facilitates rapid spread in crowded or close-contact settings. Unlike fecal-oral, vector-borne, or sexual contact routes, respiratory droplet transmission aligns with the virus’s tropism for respiratory epithelial cells. Effective prevention includes wearing masks, maintaining physical distance, and vaccination.

Reference: Harrison’s Principles of Internal Medicine, J. Larry Jameson, 20th Edition.