system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why aren’t there any medicines against the flu? And in general, against many viruses?
gpt
Viruses aren't alive so they're impossible to kill. 

Bacteria are alive, they have to take in nutrients and have many chemical processes that go on, and antibiotics are chemicals that actively disrupt those chemical processes. A virus is inert, there's nothing to turn off and they don't "eat" so you can't make them take in a poison. 

Viruses inject their DNA into a host cell and then uses your own cell's mechanisms to build more viruses. This is hard to interrupt without turning off the normal operations of your cells which you know, keeps you alive.

Many viruses can be protected against via vaccines, which "teach" your immune system to recognize the virus and destroy it. Cold and flu viruses are highly adaptable and rapidly mutate to avoid this, so getting as flu vaccine this year only protects you from a small number of flu strains and not from any new mutations of flu.

Tamiflu is a drug used to stop flu virus by interrupting the ability for new viruses to exit a host cell, slowing down the spread of the virus inside your body. It's no good to you if you take it after the flu has already spread, and doesn't work against other common respiratory viral diseases.