“The flu” is a general term for respiratory infections caused by influenza viruses. Influenza viruses are constantly changing, which means individuals can contract the flu repeatedly. Although the flu isn’t often serious in the general population, newborns, older people, and people with immune issues can develop severe (and even life-threatening) illness.[1][2]
What is the flu?
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•Last Updated: May 16, 2025
"The flu" refers to respiratory infections caused by constantly changing influenza viruses, which can lead to repeated infections. Although influenza infection is usually not serious for most people, it can pose severe risks to newborns, older adults, and people with weakened immune systems.