The real fun starts when your immune system begins to fight, this begins as soon as the flu virus starts to replicate. This can be alarming. The influenza virus has already started its own rapid replication. The immune system must generate a proper war. The virus infiltrates your lungs, throat, and nose causing inflammation, swelling and pain. In your lungs, the mucus accumulates from the inflammation that causes you to cough constantly as your body works to clear airways. And because your lungs are now damaged and vulnerable, you have a greater chance of acquiring pneumonia from an opportunistic strain of bacteria. How about the whole-body aches and pains, not to mention the fever that keeps you pinned down to the couch under a hefty load of blankets. That’s your immune system at work. The aches and pains that make you feel like you just ran an endurance run, is beneficial, because this helps to strengthen the immune system. As for the awful fever and chills you can thank your immune system again. It’s a sign that that your body is fighting its invaders. It’s strange to think that almost every awful symptom you feel during the flu is the result of your own body attempting to attack it. But consider what would happen if your body did not react this way. You wouldn’t get the nagging cough, the aches and pains, or even the persistent fever. Instead, the flu virus would continue to replicate and slowly destroy the lining of the respiratory tract or worse, allow bacteria to cause pneumonia and destroy it first. And, since you need your respiratory tract to live, you might survive to tell the tale.