FLU VIRUSES. “Influenza A viruses have caused pandemics in humans during the 20th century, such as ‘‘Spanish Flu’’ caused by the H1N1 virus that killed 25–50 million people worldwide in 1918, ‘‘Asian Flu’’ by the H2N2 virus that killed 1–4 million people in 1957, and ‘‘Hong Kong Flu’’ by the H3N2 virus that killed 0.75–2 million people in 1968. The H1N1 and H3N2 viruses still continue to circulate and cause annual epidemics that kill 0.25–0.5 million people worldwide.”
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