The smallest things in your body that have a metabolism are your cells. Cells are much much bigger than viruses. The things in your body that are the same size as viruses also do not have a metabolism.

It's sort of like there's an engine in your car. But there's not an engine in your engine, there are just parts that together make an engine. None of those parts have car-ness, but together they do. Your car has many parts all working together to make a comfortable and useful car. But the parts of the car if they are separated and just sitting on the bench, just sit there.

Viruses are like those parts, car parts. When they are not in a cell, they just sit there. But if a virus part gets into your car, it gets to participate in the metabolism of the whole car, by acting like one of the other parts and just contributing its part-in-the-system. Unfortunately, the virus part's part-in-the-system is to turn your car into a factory/machine that makes more virus parts. This is how it spreads. This is why you do not want to get a virus.

In this news story, a virus that is missing a piece of how to be a functioning part in your car, attaches to another virus that has that missing piece, and together they behave like a part that knows how to become one of your car parts.