Respiratory virus enter the body through the nose primarily. They then infect the cells lining the nose or nasal membrane. The virus multiplies inside the nasal epithelial cells and then re-emerges in the nasal passageway where virus seeks to infect more nasal cells. As virus multiplies the bodies immune system begins to immediately trap and expel part of the rapidly multiplying virus. The escaped virus now has an opportunity to infect its next host.