Antivirus can be helpful, and is important at the time of writing to install on machines and devices, but it won’t necessarily protect you.
Think of it like a flu shot, which only protects you from the known strains at the time, ie:
Swine flu vaccine won’t protect you from Bird flu.
Last year’s flu shot needs to be updated for this year’s seasonal strain.
New viruses have no vaccine until it is discovered and one is developed.
Some viruses, like HIV, switch off your systems ability to protect yourself
If already infected, your antivirus may be altered by a virus reducing or stopping your protection from other threats, even if known.
Keeping your system up to date with patches and latest versions will help this. Again, it’s not 100% bullet proof.
An attacker can train (code) the duck (virus carrier) to send itself out automatically and to change how it looks slightly each time infects a machine, say variously put on a hat, a wig, a pair of sunnies.
New unknown viruses can proliferate by being coded to ensure that when a virus is passed to another machine, it morphs sufficiently as to appear new to, and so undetectable by, antivirus. This is called Polymorphic Threat.
This issue is similar for both home and corporate networks. The only difference is corporate networks may have some monitoring software in place to detect when this is happening and prevent it from happening.
Like the firewall, antivirus needs to know what it is looking for. It’s important, therefore, to keep your antivirus up to date. It does provide some protection.
Some advertised antivirus provider and some included with their product: