What is the common cold or flu? The cold and flu are upper respiratory tract infections that are caused by viruses. Antibiotics cannot be used to fight the cold or flu because they can only kill bacteria not viruses. There can be a real danger to taking antibiotics when they are not needed. Overuse of antibiotics can lead to bacterial resistance and its ineffectiveness when we really need it. The common cold usually lasts seven to ten days and goes away with plenty of rest and fluids. You have to let the cold run its course. The cold and flu share common symptoms. However, you will feel a lot worse with the flu . Fever is very common with the flu and you also experience more aches and pains with extreme fatigue or weakness. According to the Center for Disease Control (CDC), the best way to prevent the flu is to get the flu shoot every year.