Based on CDC and WHO guidance, checked against those sources on Oct 12, 2026. Educational information only — not a diagnosis or a substitute for a licensed healthcare professional.
What it is
Flu is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness and sometimes leads to hospitalization or death, especially in young children, older adults and people with certain conditions.
How it spreads
Mainly through droplets made when people with flu cough, sneeze or talk.
Less often by touching a contaminated surface and then your mouth, nose or eyes.
People can spread flu from about 1 day before symptoms start to about 5–7 days after, and are most contagious in the first 3 days. Young children and people with weakened immune systems may spread it longer.
Symptoms usually start 1–4 days after exposure, often suddenly.
Excerpt from World Health Organization:Seasonal influenza (‘the flu’) is an acute respiratory infection caused by influenza viruses that circulate globally and year-round. It can cause illness ranging from mild to severe, sometimes resulting in hospitalization or death. Seasonal influenza activity has increased globally in recent months, with an increased proportion of seasonal influenza A(H3N2) viruses being detected. This rise coincides with the onset of winter in the northern hemisphere and an increase in acute respiratory infections caused by influenza and other respiratory viruses typically observed at this time of year. Altho
Published Dec 10, 2025 · World Health Organization — Disease Outbreak NewsShare card
Excerpt from World Health Organization:On 19 August 2024, the Viet Nam National Focal Point (NFP) for International Health Regulations (IHR) notified the World Health Organization (WHO) of a laboratory-confirmed human case of infection with swine-origin influenza A(H1N1) variant (v) virus, in the province of Son La, a northern mountainous province in Viet Nam bordering the Lao People's Democratic Republic. This is the first-ever reported human infection caused by influenza A(H1N1)v virus in Viet Nam. The source of exposure to the virus is currently unknown. According to the International Health Regulations (IHR) 2005, a human infec
Published Sep 4, 2024 · World Health Organization — Disease Outbreak NewsShare card
Current situation
32 of 123 countries with enough data are Elevated or High vs. their own historyWorld Health Organization · Oct 25, 2026
U.S.: 4 of 55 states at Moderate or above (CDC hospital admission levels)U.S. CDC · Oct 17, 2026
