Explanation:
viruses have two types of antigens: H antigens, and N antigen.
when a virus enters a cell, the stick their H antigens to the antigens of the cell. the cell sucks in the virus, while the virus is enveloped in a layer of protein. the virus sheds the protein and releases it's genes in the cell. once it's released a copy of it's genes, it exits the cell, while the H antigen is connected still to the antigen of the host cell. the N antigens act like a propeller and disconnect the two antigens and the virus goes on it's way to infect another cell.
The cell that was infected, now has the genes of the virus to copy and soon, the cell reads the genes of the virus and creates more of the virus.
there are viruses that may just inject the genes from the outside, but that makes the virus susceptible to being caught my immune cells.
Hope this helps :)
