From the Guidelines
Influenza is contagious from the day before symptoms begin and can last up to 5-6 days after onset of symptoms in adults, and up to 10 days in children.
Duration of Contagiousness
- The duration of contagiousness for influenza varies between adults and children, with adults typically being contagious for a shorter period than children 1.
- Adults can be contagious from the day before symptoms begin through approximately 5-6 days after illness onset 1.
- Children, on the other hand, can be infectious for more than 10 days after the onset of symptoms, and young children can also shed virus before their illness onset 1.
- The amount of virus excreted by an infected person drops steadily over time, with the infection risk being highest soon after symptoms develop 1.
- Severely immunocompromised persons can shed virus for weeks or months 1.
From the Research
Duration of Contagiousness for Influenza (Flu)
- The duration of contagiousness for influenza can vary depending on several factors, including the subtype of the virus and the age of the individual 2, 3.
- Studies have estimated that the infectious period for influenza can last around 1.0 day on average, with only 5% of cases being infectious for more than 2.9 days 2.
- The latency period, which is the time between infection and the onset of symptoms, can last around 1.6 days on average 2.
- Children under 6 years old have been found to have a longer duration of presymptomatic and postsymptomatic influenza virus shedding compared to adults 3.
- The duration of contagiousness can also be influenced by the use of antiviral medications, which can reduce the duration of illness by around 24 hours in otherwise healthy patients 4, 5.
- Isolation or treatment of cases within a short period after symptoms onset, such as within 16 hours, can be effective in preventing secondary cases 2.