If everyone in the world quarantined themselves for forty days?

No - the cold originated with horses and flu originated with poultry, so new viruses would mutate.

Damn, that's a shame, I could almost touch my Nobel prize for a moment.

And jump the species barrier.

nobody ever brings up that the massive flu pandemic that wiped out all those people in the twentieth century was during world war one. dead bodies in trenches were rotting and blood was in pools mixing with other stuff. it was ideal conditions for something to get a grip.