A pandemic disease is an infectious disease that spreads across multiple countries or continents, affecting a large number of people. The term "pandemic" refers to the geographic spread of the disease rather than its severity or lethality. For a disease to be considered a pandemic, it must typically exhibit sustained human-to-human transmission in diverse populations.
Several characteristics define a pandemic disease:
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Widespread Transmission: Unlike an epidemic, which may be confined to a specific geographic area or population, a pandemic affects a much larger region, often globally.
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High Infection Rates: Pandemics usually involve significant numbers of people becoming infected, often overwhelming healthcare systems.
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Sustained Human-to-Human Spread: A pandemic disease must be transmissible from person to person, allowing it to propagate through populations.
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New or Novel Pathogen: Many pandemics are caused by new strains of viruses or bacteria to which the general population has little or no immunity (e.g., influenza, SARS-CoV-2).
Historical examples of pandemics include the Black Death (bubonic plague), the Spanish flu of 1918, and more recently, the COVID-19 pandemic, which began in late 2019.