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What does low body temperature mean after high temp with the flu/covid
Executive summary
A fall from a high fever to a low or below‑normal temperature after influenza or COVID-19 can be normal part of recovery — fevers commonly resolve on their own and body temperature varies by person and time of day [1] [2]. However, abnormally low body temperature in the setting of infection has been linked in some reports to worse outcomes, and older adults often have lower baseline temperatures, so context (age, symptoms, medications, how low the temperature is) matters [3] [4].
1. What a changing temperature usually reflects: immune response and normal variation
Fever is a regulated rise in core temperature driven by the hypothalamic “set‑point” as part of the immune response to infections like flu or COVID‑19; it often appears early and then subsides as the body clears the virus [5] [2]. Normal body temperature is a range rather than a single number — commonly cited averages around 98.6°F (37°C) with typical daily variation of about 0.5°C — so a return from fever to the person’s usual baseline often simply looks like a drop on the thermometer [1] [5].
2. When a low temperature may still be reassuring
Multiple clinical sources note that many fevers “go away within a few days” without treatment and that temperatures vary person to person; post‑febrile normalization to the person’s normal or slightly lower reading is commonly reported [1] [6]. Case reports of convalescent COVID‑19 patients describe low‑grade fever during recovery that resolved without treatment, indicating diverse temperature patterns during convalescence [6].
3. When low temperature can be concerning
Some reporting synthesizing COVID‑19 data links abnormally low body temperatures (for example, under ~96.8°F / 36°C) with poorer outcomes, suggesting that failure to mount or maintain a normal febrile response — or an onset of hypothermia — may be a marker of more severe disease in some patients [3]. Harvard Health also notes that older adults commonly have lower baseline temperatures and are at risk of hypothermia, which can be dangerous if prolonged [4]. If a previously high temperature abruptly falls to an unusually low reading accompanied by worsening breathing, confusion, pallor, or other signs of clinical decline, that pattern merits medical evaluation [3] [4].
4. Role of medications and other explanations for a sudden drop
Antipyretic drugs (acetaminophen, ibuprofen) and some medications or vaccine effects can lower fever and change perceived temperature patterns; suppression of fever is common and sometimes medically-induced, which would explain a rapid fall after treatment [2] [1]. Measurement issues — different thermometers or sites (oral vs. axillary vs. ear) — also create apparent drops that may not reflect true core temperature changes (available sources do not mention specific thermometer methods in the dataset).
5. Contagiousness and recovery guidance after fever resolves
Public health guidance used during COVID‑19 and influenza seasons often used fever resolution (without antipyretics) for a defined period as one marker of reduced contagiousness; the CDC notes that being fever‑free for at least 24 hours without fever‑reducing medication typically coincides with lower contagiousness even though other symptoms or viral shedding can persist [7]. That guidance implies a falling temperature is one sign of clinical improvement but not the sole determinant of infectious risk [7].
6. Practical steps: what to watch for and when to seek care
Track the trend: know your usual baseline and note whether the low reading is near your normal or well below it; in older adults, baselines can be lower and warrant special attention [4]. Seek prompt care if low temperature is accompanied by worsening breathing, ongoing confusion, persistent weakness, signs of poor perfusion, or if temperature falls below typical hypothermia thresholds [3] [4]. If you recently took fever‑reducing medicine, remember the medication may mask fever even if infection persists [1].
7. Competing perspectives and limitations in current reporting
Clinical reviews emphasize that fever is an evolved defense and its suppression can have population‑level effects — some studies suggest blunting fever can increase transmission of influenza — while case reports and clinical guidance focus on individual assessment and safety [8] [1]. Available sources in this set document associations between low temperature and worse COVID‑19 outcomes and also describe benign convalescent temperature patterns, showing disagreement only in implication, not in basic facts [3] [6]. No provided source directly quantifies how often high fevers are followed by clinically significant low temperatures after flu/COVID, so incidence estimates are not available in current reporting (not found in current reporting).
If you want, I can summarize threshold numbers that different sources use for fever and hypothermia, or make a short checklist you can use at home to decide when to call a clinician.