What is a pandemic?

Merriam-Webster's on-line dictionary defines a pandemic as "occurring over a wide geographic area and affecting an exceptionally high proportion of the population". In terms of illness, it is an outbreak of any disease such as typhoid or influenza (the "flu"). In comparison, an epidemic is similar but the disease affects a large number of people within a population, community, or region at the same time where as a pandemic is the same disease on a much larger more global scale.

When were the last flu pandemics?

Pandemic influenzas are caused by a new strain of the influenza virus. Because […]