An influenza pandemic is described by the World Health Organization (WHO) as occurring when a new influenza virus appears and is infecting the human population who has no formerly established immunity. This results in “several simultaneous epidemics worldwide with enormous numbers of deaths and illness.” “With the increase in global transport and communications, as well as urbanization and over-crowded conditions, epidemics due to the new influenza virus are likely to quickly take hold around the world.”
According to the Centers for Disease Control and Prevention (CDC),
Common Influenza (flu) can cause mild to severe illness, and at times can lead to death. Flu is different from a cold. Flu usually comes on suddenly. People who have flu often feel some or all of these symptoms:
Fever* or feeling feverish/chills
Runny or stuffy nose
Muscle or body aches
Some people may have vomiting and diarrhea, though this is more common in children than adults.
*It’s important to note that not everyone with the flu will have a fever.