The common cold (RSV, Rhinovirus, Enterovirus, and Influenza) endlessly infects our children, our elderly, and us throughout life. This is largely due to the ability of the virus to mutate quickly, allowing the virus to escape the immunity created by the original infection. We use a method known as Sequence-based mapping which uses virus genome sequence data to understand these mutations.
Our bodies have evolved a remarkable ability to defend against the common cold. The epithelial cells lining the airways secrete antiviral proteins and viscous liquids to kill and disrupt attachment of the virus. Additionally, they physically remove viruses using cilia which beats upwards to push stuff out of the lungs. On top of this, our body contains of millions circulating immune cells that attack and adapt to the virus. Yet we still get infected by these viruses over and over.
It has been long known that the original infection by the common cold dramatically changes your immune system. This change forever alters the immune responses against future viruses. For non-mutating viruses, such as smallpox, this leads to life-long immunity. Unfortunately for us, common cold viruses quickly mutate, and our immune system can no longer adapt as well to the new virueses. Luckily, scientist in the medical sciences have figured out how we can use this to our advantage using novel vaccination strategies.