Influenza is contagious, it manifests with multiple symptoms, and it varies in severity from season to season, according to the Centers for Disease Control and Prevention. The best way to prevent influenza is to get vaccinated each season.
Patients with influenza can infect others one day before symptoms appear and five to seven days after becoming sick, reports the CDC. Young children and patients with weak immune systems may be contagious for a longer period. Influenza spreads when droplets made from an infected patient's cough, sneeze or speech land in the noses or mouths of other people nearby. It can also spread when someone touches a surface with influenza virus on it and then touches mucous membranes.
Symptoms of influenza include sore throat, stuffy nose, cough, fever and body aches, notes the CDC. Patients may also experience headaches and fatigue. Vomiting and diarrhea most commonly occur in children but can occur in adults too. Not all patients with influenza get a fever.
The severity of an influenza season depends on many factors, including how many people receive vaccinations and what viruses are spreading, explains the CDC. The time the vaccine becomes available and how well the vaccine is matched to viruses are also relevant factors.