A flu pandemic is different from a seasonal outbreak or "epidemic" of influenza. Seasonal outbreaks are caused by subtypes of influenza viruses that already circulate among people, whereas influenza pandemic outbreaks are caused by:
- New subtypes
- Subtypes that have never circulated among people
- Subtypes that have not circulated among people for a long time.
Past influenza pandemics have led to high levels of illness, death, social disruption, and economic loss.
(Click Pandemic Flu for more information about influenza pandemics.)
The reported symptoms of bird flu in humans have ranged from typical influenza-like symptoms (fever, cough, sore throat, and muscle aches) to eye infections (conjunctivitis), acute respiratory distress, viral pneumonia, and other severe, life-threatening complications.
Vaccines to protect humans against H5N1 bird flu currently are under development. In addition, research is underway on methods to make large quantities of bird flu vaccine more quickly.
So far, research suggests that two antiviral medicines, oseltamavir (Tamiflu®) and zanamavir (Relenza®), may be useful treatments for H5N1 bird flu. However, H5N1 viruses are generally resistant to two other available antiviral medications, amantadine and rimantadine, so they cannot be used to treat bird flu.