What does novel mean in novel H1N1?

The word "novel" was selected by the Centers for Disease Control and Prevention (CDC) to distinguish this H1N1 virus from all the other H1N1 viruses because the 2009 pandemic influenza it caused by a brand new type of virus.

When used as an adjective, one of the meanings of the word "novel" is "new". It is derived from the Latin word "novus" that means "new". The word novel can also mean unique, unusual, and original. All of these meanings of "novel" fit the adjective chosen to describe this pandemic influenza virus.