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How did the 2009 H1N1 outbreak spread from Mexico to other countries?
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influenza pandemic (H1N1) of 2009
Doctors at the Mexico City Navy Hospital wearing protective gear as they tend to patients complaining of H1N1 flu-like symptoms.
The 2009 H1N1 outbreak spread from Mexico to other countries primarily through international air travel. As infected individuals traveled from Mexico to other parts of the world, they carried the virus with them, facilitating its rapid global dissemination.12
The virus's spread was driven by several key factors:
- High Contagiousness: The H1N1 virus was highly contagious, with a secondary attack rateāthe frequency of new cases arising from contact with an infected personābetween 22 and 33 percent, significantly higher than that of seasonal influenza.3
- Modern Travel: The unprecedented rates of passenger travel characteristic of the modern era allowed the virus to move quickly across borders.24
- Human-to-Human Transmission: Once introduced to new regions, the virus demonstrated clear evidence of human-to-human transmission, primarily through the inhalation of infectious particles or contact with infected individuals and contaminated surfaces.13
By late April 2009, the virus had reached the United States, Spain, and several other nations, prompting the World Health Organization to declare a public health emergency of international concern.12