The illness caused by the SARS-CoV-2 virus is highly variable in its presentation, especially since the virus has evolved. While a high temperature was a hallmark symptom early in the pandemic, a significant portion of current cases do not involve a fever. Relying on temperature checks alone can lead to missed diagnoses, creating confusion for people trying to determine if they are infected.
Understanding COVID Without Fever
It is common to contract COVID-19 without ever developing a fever, defined by the medical community as a body temperature of 100.4°F (38°C) or higher. Many infected individuals remain non-febrile throughout their illness, a phenomenon more widespread with newer viral variants and high population immunity.
The body’s established immune defense, whether from vaccination or previous infection, often mitigates the inflammatory response that causes a fever. A person can be actively infected and contagious while only experiencing symptoms similar to a common cold or mild flu. Therefore, the absence of a fever should not be interpreted as the absence of COVID-19.
Non-Febrile Symptoms to Monitor
When a fever is not present, attention must shift to other symptoms, which often cluster in three main areas:
- Upper respiratory symptoms
- Systemic symptoms
- Gastrointestinal issues
Upper respiratory symptoms are highly common, including a persistent sore throat, nasal congestion, and a runny nose. The sore throat can sometimes feel sharp or painful, even with mild infections.
Systemic symptoms frequently include extreme fatigue and generalized muscle aches, known as myalgia. Headaches are also a common complaint, often presenting as a dull or persistent ache. While less frequent with newer variants, a new loss of the ability to smell or taste remains highly specific to COVID-19 and warrants immediate concern.
Gastrointestinal issues, though typically less common than respiratory complaints, can occur without a temperature elevation. These symptoms may include nausea, vomiting, or diarrhea. Monitoring the combination of these non-febrile signs is essential to identify a possible infection.
Factors Driving Atypical Presentation
The body’s response to the virus is significantly influenced by several biological and demographic factors that can suppress the normal febrile response.
Prior Immunity
Prior immunity, acquired through vaccination or previous infection, primes the immune system to respond faster and more efficiently. This rapid, targeted response often prevents the widespread inflammatory signaling necessary to raise the body’s core temperature to the level of a fever.
Age
Age is another significant determinant, as older adults, particularly those over 65, frequently exhibit a blunted immune response. Their baseline body temperature tends to be naturally lower, and their ability to generate a robust inflammatory reaction can be diminished. An older individual may have a serious infection even if their temperature remains below the clinical threshold for a fever.
Immunocompromised Status
Individuals who are immunocompromised, due to chronic medical conditions or immunosuppressive medications, may not be able to mount a typical fever response. Conditions like organ transplantation, cancer treatment, or autoimmune disorders inhibit the cellular communication pathways required to trigger a temperature increase. This reduced capacity for systemic inflammation means a non-febrile presentation may mask a more severe underlying illness.
Testing and Next Steps
If symptoms appear, assume a potential infection and proceed with testing, as symptoms alone are insufficient for a diagnosis. At-home rapid antigen tests are widely available and provide results quickly, but they are most accurate when performed multiple times over a few days. Testing should begin as soon as symptoms start, even if they are mild.
If the test result is positive, follow isolation guidelines to prevent transmission, regardless of the absence of fever. Individuals should rest, stay hydrated, and monitor symptoms carefully. Seek medical attention immediately if emergency warning signs develop, such as trouble breathing, persistent pain or pressure in the chest, new confusion, or an inability to wake or stay awake.