Antibiotics helps in stopping the usage of bio- chemical activities by the bacterias only. Virus enter the human body and uses the host cell. This would harm their own human body. That is the reason antibiotics are effective against bacteria only
Antibiotics cannot kill viruses because viruses have different structures and replicate in a different way than bacteria. Antibiotics work by targeting the growth machinery in bacteria (not viruses) to kill or inhibit those particular bacteria.