US researchers have found that some flu strains may originate in the United States and migrate to warmer climates, contrary to previous assumptions that they mostly came from China and Southeast Asia. The University of Michigan, Howard Hughes Medical Institute, and Florida State University discovered that not all flu strains in North America disappear at the end of flu season, with some traveling to South America and beyond. This may have been the case with the H1N1 swine flu pandemic. Trevor Bedford, from the University of Michigan, stated that China and Southeast Asia are significant in the influenza A migration network, but temperate regions, including the USA, also play a crucial role. Their study, published in the journal PLoS Pathogens, involved analyzing genetic sequences of seasonal flu viruses from 1998 to 2009. By creating a family tree of these viruses, the researchers gained new insights into flu, which may lead to changes in public health strategies. For instance, overusing antiviral drugs like Tamiflu could result in drug resistance if flu strains persist in the United States. Bedford stated that South America primarily gets its flu from North America, suggesting that a vaccine tailored to North American strains could be more effective for South America. The research findings could also help improve tracking of flu strains globally. Bedford emphasized the importance of understanding the origins of flu outbreaks and the need for global surveillance to effectively monitor and control the spread of the virus. The United States diagnosed the initial cases of H1N1 swine flu. Although experts are uncertain about the exact origin of the virus, genetic analysis indicates that it likely came from pigs and had been circulating for a long time before being identified.