From the Guidelines
Fever with the flu typically lasts for 3 to 5 days, with most persons experiencing resolution of symptoms after several days. The incubation period for influenza is 1-4 days with an average of 2 days 1. Uncomplicated influenza illness is characterized by the abrupt onset of constitutional and respiratory signs and symptoms, including fever, which usually begins abruptly and reaches its peak within the first 24 hours of illness. Some key points to consider when managing fever with the flu include:
- Fever usually ranges from 100°F to 102°F (37.8°C to 38.9°C) in adults, though it can sometimes reach 103°F to 104°F (39.4°C to 40°C), especially in children.
- To manage fever, medications like acetaminophen or ibuprofen can be taken, not exceeding maximum daily doses.
- Fever serves as a natural defense mechanism, helping the body fight the influenza virus by creating an environment less favorable for viral replication and enhancing immune function.
- If fever persists beyond 5 days, rises above 104°F (40°C), or is accompanied by severe symptoms like difficulty breathing or chest pain, medical attention should be sought immediately, as influenza can exacerbate underlying medical conditions or lead to secondary bacterial pneumonia or primary influenza viral pneumonia 1.
From the Research
Duration of Fever with the Flu
- The duration of fever with the flu can vary, but studies have shown that antiviral medications such as zanamivir and oseltamivir can decrease the median duration of influenza-related symptoms, including fever, by approximately 1 day if initiated within 48 hours of the onset of symptoms 2.
- A study comparing the efficacy and safety of oseltamivir and zanamivir in pandemic influenza treatment found that temperature normalization was significantly faster in patients taking zanamivir, but the overall duration of fever was not specified 3.
- There is no specific information on the number of days of fever that is common with the flu, as the studies focused on the efficacy of antiviral medications in reducing the duration of symptoms rather than the typical duration of fever itself 2, 3, 4.
Factors Affecting Duration of Fever
- The duration of fever with the flu can be influenced by various factors, including the severity of the infection, the age and health status of the individual, and the effectiveness of treatment 2, 4.
- Antiviral medications such as zanamivir and oseltamivir have been shown to be effective in reducing the duration of influenza-related symptoms, including fever, but the optimal timing and dosage of these medications can affect their efficacy 2, 3.