A cough, fever, sore throat and overwhelming tiredness can leave many people wondering whether they have COVID-19, influenza (the flu) or simply a common cold.

The challenge is that COVID-19 and flu share many of the same symptoms, making it difficult to tell them apart based on how someone feels alone. Both infections can range from mild illness to serious disease, particularly among older adults, young children, pregnant women and people with underlying health conditions.

While certain patterns may offer clues, testing remains the most reliable way to identify the cause of symptoms and determine whether specific treatments are needed.

'The truth is that because fever, cough, body aches, sore throats, headaches, and fatigue can be found in both illnesses, testing is the only real way to determine the diagnosis,' said Dr James Lyons, MD, clinical advisor at Epiphany Wellness.

COVID vs Flu: What Are the Main Differences?

COVID-19 is caused by the SARS-CoV-2 virus, while influenza is caused by influenza viruses. Both primarily affect the respiratory system and spread through respiratory droplets and airborne particles released when an infected person talks, coughs or sneezes.

Although the illnesses overlap significantly, one noticeable difference can be how symptoms begin.

'One clinical distinction between the two viruses is the suddenness of onset,' Dr Lyons explained. 'Influenza tends to come on quickly. Many of my patients can recall exactly when their illness began.'

Flu symptoms often appear abruptly, with people describing a sudden feeling of being extremely unwell. COVID-19, however, can have a wider range of presentations, from mild symptoms to more prolonged illness.

'While COVID-19 can certainly start rapidly, it also presents in many different forms of illness from mild to severe over an extended period of time,' Dr Lyons said.

Common Symptoms of COVID-19 and Flu

Both COVID-19 and influenza can cause:

  • Fever or chills
  • Cough
  • Sore throat
  • Headache
  • Fatigue
  • Muscle aches and body pains
  • Runny or blocked nose
  • Reduced appetite

COVID-19 may also cause symptoms such as changes in taste or smell, although these signs are less common than earlier in the pandemic.

Flu is often associated with stronger body aches and sudden exhaustion, while COVID-19 symptoms can vary more widely between individuals.

However, there is no symptom that can definitively confirm one infection over the other.

'Patients ask me every day if, based on their symptoms, they have the flu, COVID, or simply a cold,' Dr Lyons said. 'Testing is especially important for those who would likely need antiviral therapy.'

Why Testing Matters

Because COVID-19 and flu symptoms overlap, healthcare professionals recommend testing when possible, particularly for people at higher risk of complications.

A correct diagnosis can affect treatment decisions. Antiviral medicines are available for both influenza and COVID-19, but they are most effective when started early in the illness.

Dr Lyons highlighted that identifying who needs treatment quickly is often more important than focusing only on which virus caused the symptoms.

'Older adults, pregnant women, young children and individuals with ongoing medical issues are all at increased risk of developing serious disease from both viruses,' he said.

For people in these groups, contacting a healthcare professional early may allow treatment to begin before symptoms worsen.

Who Is Most at Risk of Severe Illness?

Sick Senior / COVID-19 / Flu
COVID-19 and flu can become serious, especially for older adults, pregnant women, young children, immunocompromised people and those with chronic health conditions. Drazen Zigic via Magnific

Although healthy adults often recover without complications, both COVID-19 and flu can become serious.

People at increased risk include:

  • Adults aged 65 and over
  • Pregnant women
  • Young children, particularly infants
  • People with weakened immune systems
  • Those with chronic conditions such as asthma, COPD, diabetes or heart disease

Severe respiratory infections can lead to complications including pneumonia, worsening of existing medical conditions and, in some cases, hospitalisation.

How Are COVID and Flu Treated?

Treatment depends on the severity of symptoms, the person's risk factors and how early medical advice is sought.

For mild cases, recovery often involves:

  • Rest
  • Drinking plenty of fluids
  • Managing fever and discomfort with appropriate medicines
  • Monitoring symptoms

For people at higher risk, antiviral treatments may be recommended.

Flu antivirals, such as those prescribed by healthcare professionals, work best when started within the early stages of infection. COVID-19 antiviral treatments may also be offered to eligible patients who are at increased risk of severe disease.

This is why early testing and medical advice can be important.

When Should You Seek Medical Help?

Most people with COVID-19 or flu recover at home, but some symptoms require urgent medical attention.

Seek medical advice if you experience:

  • Difficulty breathing
  • Chest pain or pressure
  • Confusion or disorientation
  • Signs of dehydration
  • Symptoms that worsen after initially improving
  • Persistent or severe symptoms

'Symptoms such as difficulty breathing, chest discomfort, disorientation/confusion, persistent dehydration or worsening symptoms after an apparent recovery should prompt immediate medical consultation,' Dr Lyons advised.

People with risk factors for severe illness should contact a healthcare professional sooner rather than waiting for symptoms to become severe.

Common Myths About COVID and Flu

One misconception is that flu is simply a 'bad cold'. While flu symptoms can sometimes be mild, influenza can cause serious illness.

'Both influenza and COVID-19 can result in hospitalisations and death; severe cases do occur and particularly in high-risk populations,' Dr Lyons said.

Another misconception is that people can always tell which virus they have based on symptoms alone. In reality, overlapping symptoms make testing essential.

Preventing COVID and Flu

Vaccination remains one of the most effective ways to reduce the risk of severe illness from both viruses.

Other preventative steps include:

  • Washing hands regularly
  • Improving indoor ventilation
  • Avoiding close contact when unwell
  • Covering coughs and sneezes
  • Staying home when experiencing symptoms

'The most effective method to reduce severe illness due to either virus is vaccination, prompt medical care, and emergency care when appropriate,' Dr Lyons said.

The Bottom Line

COVID-19 and flu can look very similar, making it difficult to know which infection you have without testing.

While flu often develops suddenly and COVID-19 can vary more widely in its presentation, symptoms alone are not enough to make a reliable diagnosis.

For most people, rest and supportive care are enough. But for those at higher risk, early testing and medical advice can make an important difference by allowing timely treatment and reducing the risk of serious complications.

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