Flu is an infectious disease caused by the influenza virus. The commonest symptoms are: rapid onset of fever, shivering, headache, muscle aches, and a cough. These symptoms typically begin 1–4 days after exposure to the virus and last for about 2–8 days. Flu causes a much more severe illness than the common cold: a cold doesn’t cause fever or muscle aches. People with flu can feel very ill indeed, often resulting in several days of being confined to bed. It infects people of all ages but tends to disproportionately cause severe illness in the elderly, the very young, and those who have chronic health issues.
Most people recover easily, but would have much preferred to avoid the experience altogether, which is where the flu vaccine comes in.
For some victims, flu can cause more serious complications, like bronchitis and pneumonia and can worsen existing medical conditions such as asthma and cardiovascular disease. It can be potentially life-threatening in the elderly, asthmatics and those with pre-existing medical conditions.
Each year, influenza-associated deaths range from 290,000 to 650,000 globally, and the burden on hospitals is around 10 million influenza-related hospitalizations. Recent studies also show that influenza can multiply the risk of heart attack by up to 10 times, and the risk of stroke by up to 8 times, during the week after influenza infection – demonstrating that the burden of flu goes beyond its well-known respiratory complications.