Influenza is a contagious respiratory illness caused by influenza types A or B viruses. Influenza viruses are easily spread by airborne respiratory droplets from person to person (often by sneezing or coughing).
Symptoms of infection include fever, muscle aches, headache, malaise (a general feeling of sickness), nonproductive cough, sore throat, and runny nose. The flu causes mild illness in most people, the majority of whom will not need medical care or antiviral drugs, and usually recover in less than two weeks. Some people, however, can suffer flu complications that result in being hospitalized. Sometimes influenza infection results in death.
Pneumonia, bronchitis, sinus infections and ear infections are examples of more severe flu-related complications. The flu also can make chronic health problems worse. For example, people with asthma may experience more frequent asthma attacks while they have the flu. The flu may also worsen congestive heart failure in people with this condition.
Influenza viruses are constantly changing, so it is not unusual for new strains of influenza virus to emerge at any time of the year. This year's influenza vaccines were made using the following strains:
The B/Massachusetts and B/Brisbane strains are a change from last year's formulation.
Children younger than 5 but especially children younger than 2 years of age, adult 65 years and older, pregnant women and individuals with various chronic medical conditions are at greatest risk for hospitalization and possibly death related to infection.
A full list of high-risk conditions can be found at: www.cdc.gov/flu/about/disease/high_risk.htm