HONG KONG FLU This strain killed an estimated 1m people worldwide.
BIRD FLU Between 2005 and 2007 Britain braced itself for an avian flu outbreak.
Swine flu killed 209 people in Britain, although the spread was not as bad as initially feared.
The NHS says: "It spread rapidly from country to country because it was a new type of flu virus that few young people were immune to.
One of the oldest and most common diseases known to man, flu is a notorious killer.
In 1976, just when health experts globally were ready to close the chapter of the early 1900 plague, an American soldier mysteriously died of flu. He suffered lung bleeding and died after five days.
In 1988, the avian flu killed five Hong Kong locals and infected hundreds of residents, prompting health officials here to dig deeper on the real cause and activity of the bird-flu virus.
Moreover, like colds, flu can be transmitted by people who have not yet developed symptoms.