What energy does the flu virus use?

Answer 1

It uses the energy of a host cell, in a sort of parasitic way.

A virus is non-living, although it is a well structured organism able to reproduce and cause things to happen. To do these things, it does not generate or use its own power or energy. Instead, it invades a living host (a plant, animal or human) and attaches a virus particle into a cell and makes that living cell of the host to which it has attached change its operations from working for the host to working for the virus.

The cell begins to create duplicates of the virus particles. It does this because once the virus has attached itself, it adds part of its own DNA or RNA instructions into the cell which turns the cell into a virus-making factory. The cell's original DNA is no longer giving the instructions to the cell and so it is no longer doing what it is supposed to for the host and eventually dies when it bursts open to release the virus "babies".

This is what makes us get sick if enough of our cells are pulled off their usual jobs by the virus and made to do other things and then die. All the energy that is needed to reproduce the virus is supplied by the host cell, and as it produces new virus particles those "offspring" attach to more cells and the process repeats cell by cell particle by particle as it moves through our bodies and attaches to more cells. Eventually (hopefully) our body's immune system learns the key to turning the virus off (or "killing" it). If too many of our cells are diverted before the immune system figures out how to attack the virus to stop it, then we can have organ and system failures and that is how we get very ill or even die.