Yes and no. The Spanish flu was H1N1. And while it was murderously lethal, it still only reproduced in the UR tract and sinuses.
However, the H7 equine *and* H5, of the now menacing Avian flu, have both been found reproducing in internal organs. This is very bad.
The real world difference might be seen in mortality rates. As vicious as the Spanish flu was, it only killed about 18% of those who were infected. So far, H5N1 has mysteriously maintained an over 60% mortality.
With an effective Human to Human transmission, the world is facing mortality numbers not expected outside of a nuclear war. Concentrated mostly in Asia, 300m fatalities may be a good starting estimate.
Horses originally evolved in the Americas, crossed the land bridge to Asia, and thrived. Somewhere along the line, every horse in the Americas died. I don’t think the cause was hunting to extinction. Lethal bugs could be a major factor in evolution and species extinction. The biggest threat to civilization is not terrorist nukes but bio gone wrong...either human-created in the lab or by natural means.