Great question! Unlike a vaccine, which stimulates your immune system by introducing a part of a virus into your body, antiviral drugs rely on other methods of stopping a virus in its tracks. Because viruses need host cells to replicate and survive in a body, blocking the viruses from entering these host cells or preventing replication are effective means of preventing the virus from spreading and making you sick.

Some antivirals will interfere with a receptor that the virus needs to enter the cell. Some antivirals will interact with parts of the virus itself to disrupt its function. Several antivirals interfere with virus-associated enzymes needed for the virus to reproduce, or infect neighboring cells.

For instance, the anti-COVID drug Remdesivir works by interfering with an enzyme the virus needs to replicate its RNA genome. Through these mechanisms, antiviral drugs are effectively able to stop a viral infection. Hope this helps!