Not every virus wants to go viral — at least, not immediately. Some want to slip in quietly. Hide. Wait for the perfect opportunity to attack.
In order to do so, the virus has to find a way to enter the cells of the human body without tripping the alarm, and stay there without notice. It’s how HIV works, and also how viruses in the herpesvirus family, like human cytomegalovirus (HCMV), do their business.