The strain of virus responsible for the 2009 H1N1 pandemic has passed from humans to swine nearly 400 times, according to a new study.
The US-based team tracked the swine flu strain pdm09 between the years 2009 and 2021 to offer insights into its transmission.
After being passed from humans to pigs, the circulation of pdm09 among swine resulted in some variants that then jumped back to humans, the study showed.
