According to US researchers, the United States may act as a breeding ground for certain flu strains, allowing them to move to warmer regions. Previous assumptions suggested that flu strains mainly originated in China and Southeast Asia. However, a team of researchers from the University of Michigan, the Howard Hughes Medical Institute, and Florida State University discovered that some flu strains in North America do not disappear at the end of flu season. Instead, some of these strains travel to South America and possibly even further. This phenomenon may have occurred during the H1N1 swine flu pandemic. Trevor Bedford of the University of Michigan conducted a study on the migration network of influenza A, finding that China and Southeast Asia are key players, but temperate regions, including the USA, also have a significant impact. The study, published in the journal PLoS Pathogens, analyzed genetic sequences of seasonal flu viruses worldwide from 1998 to 2009 to create a family tree of virus relationships. The findings suggest that public health officials may need to adjust their strategies for fighting the flu, as aggressive use of antiviral drugs like Tamiflu could lead to drug resistance if flu strains persist in the United States. Bedford stated that South America primarily gets its flu strains from North America, suggesting that a tailored vaccine could be created using strains from North America. The team also mentioned that the research could improve tracking of flu strains globally, revealing that flu can originate from temperate regions in addition to Southeast Asia. This highlights the need for more comprehensive global surveillance. The initial instances of H1N1 swine flu were identified in the United States. The exact source of the swine flu is still unknown, but genetic research indicates that it likely originated from pigs and had been spreading for several years prior to being identified.