COVID vs flu vs viral fever: How to spot the difference and new symptoms to watch for

As respiratory infections continue to circulate, many people struggle to tell whether they have COVID-19, influenza or a common viral fever. A physician explains the symptoms, warning signs and when it's time to get tested.

In Short

• COVID-19 now often begins with upper respiratory symptoms and gradual onset
• Flu usually strikes suddenly, causing high fever, chills and severe aches
• Common viral fevers are milder and usually ease within three days

With changing weather and an increase in seasonal infections, clinics are once again seeing people with fever, sore throat, cough and body aches. For most people, the biggest question is simple: Is it COVID-19, the flu, or just a viral fever?

The challenge is that these illnesses often begin with similar symptoms, making it difficult to know exactly what is causing the infection during the first few days. While many viral illnesses can be managed with rest and fluids, COVID-19 and influenza can sometimes lead to complications, particularly in older adults, pregnant women, young children and people with chronic illnesses.

Doctors say that although these infections overlap in many ways, there are important differences in how quickly symptoms appear, how severe they become and how long recovery takes. Paying attention to these clues and seeking medical advice when needed can help people receive the right treatment while reducing the risk of spreading infection to others.

According to Dr Shridhar Deshmukh, MD General Medicine, Consultant Physician and Intensivist at Ruby Hall Clinic, Pune, COVID-19 today does not always look the way it did during the early days of the pandemic. While severe disease is less common in many people, the virus continues to evolve, and its symptoms can still differ from influenza and other viral infections.

COVID-19: SYMPTOMS HAVE CHANGED, BUT IT CAN STILL CAUSE PROLONGED ILLNESS

One of the biggest changes doctors have noticed is that COVID-19 often starts with symptoms affecting the upper respiratory tract.

People with COVID-19 may experience:

• Persistent sore throat
• Dry or lingering cough
• Stuffy or blocked nose
• Headache
• Fever
• Body aches
• Extreme tiredness
• Loss of appetite
• Nausea or diarrhoea in some cases

Unlike influenza, COVID-19 symptoms often develop gradually over a day or two instead of appearing suddenly.

Another feature that still sets COVID-19 apart is fatigue. Even after the fever and cough improve, many patients continue to feel exhausted for days or even weeks.

"COVID-19 is not just another viral infection. While many people recover without complications, it can leave patients feeling weak for a prolonged period," says Dr Deshmukh.

INFLUENZA: A SUDDEN ILLNESS THAT HITS HARD

Influenza, commonly known as the flu, usually announces itself much more dramatically.

A person may feel perfectly healthy in the morning and develop high fever, chills and severe body aches by the afternoon.

Common flu symptoms include:

• Sudden high fever
• Chills
• Severe muscle pain
• Headache
• Dry cough
• Sore throat
• Runny nose
• Extreme weakness

Doctors say the speed of onset is one of the easiest ways to distinguish influenza from COVID-19.

Although the flu can make people feel extremely ill, most healthy adults begin recovering within five to seven days.

WHAT ABOUT OTHER VIRAL FEVERS?

Many common viruses, including adenovirus, enterovirus and parainfluenza viruses, can also cause fever and respiratory symptoms.

Typical symptoms include:

• Mild to moderate fever
• Sore throat
• Runny nose
• Mild cough
• Body aches
• Occasional stomach upset

Compared with influenza, these illnesses are generally milder and improve within three to five days with supportive care such as:

• Adequate rest
• Drinking plenty of fluids
• Fever-reducing medicines as advised by a doctor
• Nutritious meals

Unlike COVID-19, these infections usually do not leave people with prolonged fatigue.

COVID VS FLU VS VIRAL FEVER: KEY DIFFERENCES

CAN YOU HAVE MORE THAN ONE INFECTION?

Doctors say it is becoming increasingly common for several viruses to circulate at the same time.

This means a person may:

• Have both COVID-19 and influenza together.
• Develop another viral infection soon after recovering from one.
• Get a bacterial infection following a viral illness.

Because symptoms overlap so much, it is often impossible to know the exact cause based on symptoms alone.

Testing may be necessary, especially for people at higher risk of complications.

WHO SHOULD GET TESTED?

Testing is particularly important if you are:

• Pregnant
• A young child
• An older adult
• Living with diabetes, heart disease or lung disease
• Immunocompromised
• Caring for elderly family members

Getting tested early helps doctors decide the best treatment and reduces the risk of spreading infection to others.

WARNING SIGNS YOU SHOULD NEVER IGNORE

Regardless of whether the illness is COVID-19, influenza or another viral infection, some symptoms require immediate medical attention.

Seek medical care immediately if you experience:

• Fever lasting more than three days
• Difficulty breathing
• Chest pain
• Confusion or excessive drowsiness
• Severe dehydration
• Persistent vomiting
• Bluish lips or fingertips
• Symptoms that worsen after initially improving

These signs could indicate complications that need urgent treatment.

HOW TO PROTECT YOURSELF

Doctors recommend the following simple precautions to reduce the risk of respiratory infections:

• Wash your hands regularly.
• Cover your mouth and nose while coughing or sneezing.
• Wear a mask if you have a fever or a cough, especially in crowded places.
• Stay home when you are sick.
• Drink enough fluids and get adequate sleep.
• Keep vaccinations against influenza and COVID-19 up to date if recommended by your doctor.

Fever, cough and body aches no longer point to just one illness. COVID-19, influenza and other viral infections can all begin with similar symptoms, making self-diagnosis difficult.

While common viral fevers usually improve within a few days, influenza tends to strike suddenly with intense body aches, whereas COVID-19 often develops more gradually and may cause lingering fatigue and respiratory symptoms. If symptoms are severe, persist beyond a few days or occur in someone at high risk, early medical evaluation and testing are the safest approach.

As Dr Shridhar Deshmukh advises, rather than trying to identify the illness based on symptoms alone, it is better to seek medical care early. A timely diagnosis not only helps ensure appropriate treatment but also prevents the infection from spreading to family members and the wider community.

- Ends