If a baby has a cold and a high fever, it's generally hard to say how many days it will last. If infected by a virus or bacteria, the virulence and the body's immune function are both factors. If the viral strength is weak and the body's resistance is strong, with the appropriate use of medications, the fever can typically be controlled within one to three days. However, if the infection is due to stronger viruses or bacteria, such as the influenza virus, the common fever duration is around five to seven days, or even longer. So, for a common cold, the fever may last about three days, while influenza may last four to five days or even longer.