When is influenza contagious?

• A. 24 hours before symptoms begin and up to 5 days after they begin
• B. Only after symptoms begin
• C. Only after fever develops
• D. 1 week after exposure

Answer: (A)

Influenza can spread before you even feel sick and remains contagious for several days after symptoms start. The best answer captures both sides of this reality: you can be contagious about a day before symptoms and typically continue to shed the virus for about five days after symptoms begin. This reflects how viral shedding drives transmission, not just the presence of fever or when symptoms first appear.

Why the other ideas don’t fit: contagiousness isn’t limited to after symptoms or only after fever, because people often spread the virus before fever or even before they notice symptoms. Saying it’s contagious only a week after exposure doesn’t align with the usual window of viral shedding, which starts before symptoms and ends a few days into illness.