Pandemics are different from normal infectious diseases, as they are generally new diseases that emerge from wild animals and spread to humans through contact. The viruses mutate and eventually start spreading within the human population.
Pandemics require the outbreak to reach a certain scale before taking off. When the number of cases exceeds the expected level, emergency plans are activated at hospitals and regional and national levels to cope with the increased numbers of people seeking treatment.
The virus strain that hits the population during a pandemic is radically different from the strains that have been circulating previously. This lack of prior immunity leads to higher infection rates and an increased number of people requiring hospitalization.
Historically, pandemics have caused devastating effects. The Black Death, which killed at least 75 million people in the 14th century, serves as a stark reminder of the potential impact of pandemics in the modern world.
Influenza is one of the most common viruses that cause pandemics. The influenza virus regularly mutates into new strains, for which the general population has no natural immunity. This results in widespread infection and high mortality rates.