How contagious is the 24 hour flu?

The "24-hour flu" is not a real medical condition. While seasonal flu can cause symptoms that may last up to 24 hours, it is not a separate illness. The flu is a viral infection of the respiratory tract caused by influenza viruses. It can be highly contagious, especially during the flu season, and can spread from person to person through close contact, such as coughing, sneezing, or talking, or by touching surfaces or objects contaminated with the virus.