Why virus is imortal?

Strictly speaking, viruses can't die, for the simple reason that they aren't alive in the first place. Although they contain genetic instructions in the form of DNA (or the related molecule, RNA), viruses can't thrive independently. Instead, they must invade a host organism and hijack its genetic instructions.

Explanation:

A flu is a virus and the reason that you have to get flu shots every year is because every time a virus enters a host it is mutated by the antibodies, cells and biology of that host, so it can be passed on to another host who may not be immune to every part of this NEW virus.

Explanation:

So your answer is both yes and no.

a covalent bond, specfically triple bond