Answer:
Influenza pandemics occur when a new strain of the influenza virus is transmitted to humans from another animal species. ... These novel strains are unaffected by any immunity people may have to older strains of human influenza and can therefore spread extremely rapidly and infect very large numbers of people.
(I found this on google, this is not my own idea)
Answer:
a strain of flue infects many people all over the world.
Explanation:
