Myth: Antibiotics can kill the germs that cause colds and the flu. 

Reality: American doctors write millions of antibiotic prescriptions for colds and flu every year. But no antibiotic will help a cold or flu because they only do one thing: kill bacteria. And colds and flu are caused by viruses, a class of germs that aren’t anything like bacteria. Unless your child has a complication of a cold or flu that might involve bacteria, antibiotics are not a good solution for treatment. 

Source: https://www.avera.org/services/wellness-preventive/health-wellness-information/the-truth-about-colds–flu/