A virus first has to be able to get into a cell. But it can only do this if its antigen fits into one of the cells receptors. Depending on how much the cell has and of different types. Once the virus is in it replicates its DNA and proteins. Then these assemble and make even more viruses. The viruses then leave the cell. And all the viruses go off to infect a new cell and replicate more viruses.
