However, there are vaccines which have some protective effect. These are normally administered to the elderly and the vulnerable each year. But every few years a new strain of flu appears which spreads so rapidly that precautions cannot be developed in time. This can lead to pandemics which threaten millions of lives. The worst flu pandemic this century was the Spanish flu pandemic of 1918 which killed an estimated 40 million people - more than World War One.
Many people confuse flu with a common cold.
There is a big degree of crossover between the two. Both are caused by viruses. Both colds and flu tend to last for about five or six days in a normally healthy person and are transmitted in similar ways - cough, sneezing and fingers made dirty from being poked in the nose and eyes. The most difficult symptoms to treat are aches and pains, high fever and a lingering cough. This should relieve the aches and pains and will ensure the virus is not spread.