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The influenza A viruses endemic in many animal species can spread from animals to humans and among humans. Numerous cases of animal-origin influenza in humans have been documented over the last 2 decades. Sources have included birds (H5N1, H7N7) and swine (H1N1, H1N2, H3N2).
Now, the CDC reports two epidemiologically independent cases of swine-origin influenza that occurred in July–August 2011 — one in an Indiana boy aged <5 years who had no direct contact with swine, and the other in a Pennsylvania girl aged <5 years who had had contact with swine at a state fair 4 days before symptom onset. Both children had received influenza vaccine in September 2010.
The viruses were identified as swine-origin H3N2 by the respective state health departme…