Researchers in the United States have discovered that some flu strains may originate in the country and then migrate to warmer climates. This challenges the previous belief that most flu strains came from China and Southeast Asia. A team from the University of Michigan, the Howard Hughes Medical Institute, and Florida State University found that certain flu strains in North America do not disappear at the end of flu season; instead, some travel to South America and beyond. This migration pattern may have been observed during the H1N1 swine flu pandemic. Trevor Bedford of the University of Michigan, along with his colleagues, discovered that China and Southeast Asia are major players in the influenza A migration network, but temperate regions, particularly the USA, also play a significant role. Their study, published in the Public Library of Science journal PLoS Pathogens, involved analyzing genetic sequences from seasonal flu viruses collected worldwide between 1998 and 2009. By creating a family tree of the viruses, they gained new insights into the flu virus, which may require public health officials to adjust their strategies for combating the flu. For instance, the overuse of antiviral drugs like Roche AG's Tamiflu could lead to drug resistance if flu strains persist in the United States. Bedford stated that their research revealed that South America primarily receives flu strains from North America. As a result, they suggest creating a vaccine based on North American strains rather than using the same vaccine as the rest of the world. The team also emphasized the importance of tracking flu strains more effectively to better understand their origins and spread globally. Bedford highlighted the need for global surveillance, as flu strains can originate from various regions, not just Southeast Asia. The United States diagnosed the first cases of H1N1 swine flu. Its origins are still unknown, but genetic testing indicates that it likely came from pigs and had been present for a long time before being discovered.