 Viruses consist of a genome and sometimes a few enzymes stored in a capsule made of protein (called a capsid), and sometimes covered with a lipid layer (sometimes called an 'envelope').Viruses cannot reproduce on their own and instead propagate by subjugating a host cell to produce copies of themselves, thus producing the next generation.Researchers working on such "rational drug design" strategies for developing antivirals have tried to attack viruses at every stage of their life cycles.