As seasonal flu activity intensifies and Covid-19 remains present, many people are once again asking the same question: how can you tell which virus is causing your symptoms? According to medical experts, the answer is not always straightforward—and testing is often essential.

Both flu and Covid can cause cough, fatigue, shortness of breath, runny nose, headache, body aches, sore throat and even gastrointestinal symptoms such as abdominal pain or diarrhea. Loss of smell may occur in both illnesses, although it is now less common in Covid cases than during the early years of the pandemic. As specialists note, there is no single symptom that clearly distinguishes one infection from the other.

One potential clue is how symptoms begin. Covid often develops gradually, starting with mild congestion or a sore throat before worsening. The flu, by contrast, typically strikes suddenly, with patients reporting intense exhaustion and body aches from the outset. Fever can occur in both cases, though it tends to appear earlier with the flu.

Despite these differences, doctors stress that symptoms alone are not enough. Rapid self-tests for Covid remain widely available, and combination tests that detect both Covid and flu can provide results within minutes. Because early testing may produce false negatives, repeat testing after 48 hours is recommended if symptoms persist.

Testing is especially important for people at higher risk, including older adults, pregnant women and those with underlying health conditions, as it allows timely access to appropriate antiviral treatment. Experts also emphasize prevention measures such as vaccination, hand hygiene, ventilation and staying home when ill, noting that it is still beneficial to receive both flu and updated Covid vaccines.