The influenza virus, commonly known as the flu, is a difficult virus that can cause more than just pain and misery for a long period of time. In those who are very young or very old, it can be deadly. It is so difficult to treat because the virus itself changes rapidly. Every year, the strain that affects humans is different, and so it is difficult to develop the perfect vaccine. Additionally, drugs that target viruses are difficult to create, because many viruses work by getting into your body and making your body do the work of making more viruses.
In other words, viruses are so good at making you sick because they convince the cells of your body to keep helping to make you sick. Your body fights back by making antibodies to the virus, which is the perfect fix. Unfortunately, making antibodies takes lots of energy, and causes you to feel even more tired. Additionally, the process of making them does take a few days. For that reason, you are almost always doomed to a few days of misery with any viral infection.
Speaking to your doctor
soon after getting an infection can sometimes help, if it happens early enough - so make sure to speak with your doctor quickly if you think you have the flu.