How is the viral syndrome different from the flu?

Different virus: True flu is caused by an influenza virus infection whereas the viral syndrome (flu-like syndrome) by infections associated with a variety of viruses.

Typical vs vague: The flu (A or B) has dramatic often abrupt signs that fall into typical patterns. They also may respond to anti-flu meds if given very early in the course. A viral syndrome is a broad umbrella label that encompasses dozens of separate families of viruses that effect many systems of the body. Their features/duration vary & there are no specific meds to alter the pattern.