You’re jumping on a sinking ship here. “Human H1N1” does not refer to “The only strain of H1N1 that can be contracted by humans.” It’s talking about the origin of the strain. H1N1’s origins are not known for sure, but there was a strain circulating in humans for 90 years that was simply H1N1. It’s now gone. H1N1pdm09 is a different strain that had been circulating in swine until it jumped to humans in 2009, and thus the name swine flu.