Becuase the flu is unique in this regard, it divides and recombines as a matter of course, that's why they number the combinations, like h1n1, h1n2, etc. Most o

Becuase the flu is unique in this regard, it divides and recombines as a matter of course, that's why they number the combinations, like h1n1, h1n2, etc. Most other viruses, including coronaviruses, don't do that like the influenza does.