Joe,
It is the virus that is swapping genes.
The two strains appear to be mixing genes among primate populations.
This recombinant behavior (Dr. Niman please pick up the white courtesy phone) is a worst case scenario.
We need a stable genome to target.
When the target is constantly shifting many bad things can happen. including variations that require less contact for infection.
MA
Aw, Mom! It's no more difficult than finding a vaccine for the common cold...