Siegel noted that these flu strains have not been the cause of flu pandemics in the past.
"There is probably a genetic reason why all human flu pandemics have been H1, H2 and H3 strains and not H5 and H7," he said.
"It's really unlikely that these mutations will occur naturally in either of these viruses," Siegel said. "People should be reassured that scientists are studying this."
For more about the flu, visit the U.S. Centers for Disease Control and Prevention.
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