The capsid is the protein shell that surrounds the core of a virus where its nucleic acid is located. The capsid is made up small sub units called capsomeres.
A virus consists of a nucleic acid which may either be RNA or DNA and is found in varying quantities in the virus. It is this nucleic acid that is vital to the virus' survival that is housed in the capsid.
A drug that targets the capsid and damages it will cause the nucleic acid to leak out of the virus and into the surrounding while other fluids foreign to the virus will get in rendering the virus totally impaired, and due to this the virus cannot survive but will speedily die.
