Flu is the common name for illness caused by the influenza virus. It brings on headache, muscle ache, sore throat, runny nose and cough. It's much worse than the common cold, often requiring a few days in bed, struggling with fever, poor appetite, and feeling very tired and drained. It comes in the winter, it's highly contagious and most people have experienced it at one time or another. If you're healthy, you have a miserable 2 to 7 days then get better and back to normal life. The risk comes to those who are elderly or have ongoing medical conditions. It can also hit those with suppressed immune systems hard, either from conditions or medication. It causes inflammation in the lungs and airways, leading to breathing problems, pneumonia and even death. Antibiotics won't help as they don't work on viruses, only bacteria. Your immune system will fight it off, and you may need intravenous fluids and oxygen if you are admitted to hospital.
The virus is clever: it changes to make sure it survives and continues infecting, so even if you’ve had flu once or been vaccinated the year before, you are not immune. The vaccine gets updated every year with new strains to protect you each winter.
A small injection is given in the fleshy part of your upper arm using a very fine needle. You need a new injection every year to remain protected.
The vaccine is considered very safe, millions of people receive it every year, and most people have no side effects at all. Some feel a bit sore around the injection site, and it might become a bit hard and pink for a few days. A small number experience sore muscle, as their immune system mounts a response.
You cannot catch flu from the adult vaccine, as it does not contain “live” virus. But lots of people report getting the flu and at that time of year and attribute it to the vaccine, when in reality, the vaccine is usually circulating in autumn at high levels, so it's more likely they've caught the virus before the vaccine has had a chance to build immunity.