A virus is an acellular structure which is a non-living particle outside of the body of its host. Thus, it lacks protoplasm which is the site of most of the metabolic activities, antibiotics which are effective against bacteria (living prokaryotic cell), are ineffective on viruses. Viruses don't have cell walls that can be attacked by antibiotics instead, they are surrounded by a protective protein coat, Unlike bacteria, which attack your body's cells from the outside, viruses actually move into the body cell and make copies of themselves in your body's cells.