Usually, about 10,000 people die every year from complications of the flu. Flu epidemics usually occur from December through February, but several years ago it started in September. Influenza accounts for millions of days lost from work each year. Etiology Influenza A is caused by a virus that is able to change slightly from year to year so that a new vaccine has to be given every year to maintain protection. Viruses are very small germs that are much smaller than bacteria.
Viruses are responsible for the bulk of colds and other childhood illnesses.
Influenza B is also responsible for a flu-like illness, but it is not as severe as the Influenza A strain. The symptoms of Influenza A are fairly typical and initially consist of fever, muscle aches, headache, malaise and a dry cough. Following this is a sore throat, runny nose and sometimes nausea and vomiting. Influenza is spread from person to person by direct contact, large droplet infection, or articles recently contaminated by nasal secretions. People are infectious from 24 hours before the onset of symptoms until about 7 days after the infection starts.