Explanation

A virus is a germ that can cause infections like chicken pox and measles.

Each virus particle contains a recipe for making copies of itself. Viruses have keys that can line up with the lock on the surface of your cells, and if there is a match, the key opens the lock and the virus enters the cell! The virus then uses the ingredients inside to make millions of clones of itself.

These burst out of the cell, and infect more and more other cells and eventually cause a viral infection! There are loads of different viruses, but your immune system keeps them in check!