Flu (Influenza)

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Symptoms

Flu symptoms usually begin suddenly. 

Symptoms can include

  • Fever or feeling feverish and chills (not everyone has a fever)
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle or body aches
  • Headache
  • Fatigue (feeling very tired)
  • Vomiting or diarrhea

Some older adults may not show typical signs of infection. Up to half of frail older adults do not develop a fever, even when they have a serious infection.

Fever

In most adults, a fever is defined as a body temperature of 100.4°F (38°C) or higher. However, in frail older adults, a fever may be defined differently. It may include:

  • A temperature that is more than 2°F higher than the person’s usual body temperature
  • A single temperature reading above 100°F
  • Repeated temperature readings above 99°F  

 

Last Updated April 2026

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