Flu or Covid-19? How to tell the difference - symptom differences explained by experts

Flu and Covid-19 are both in high circulation this year, with the UK experiencing its first winter without coronavirus measures in place. The UK Health Security Agency (UKHSA) also recently warned that flu, or influenza to give it its full name, is now putting more people in hospital than coronavirus.

But for those currently feeling under the weather, you may be wondering if it’s flu or Covid - and how the symptoms differ.

We spoke to experts to find out the difference between the two viruses and how symptoms may vary. Here’s what you need to know.

How can I tell the difference between flu and Covid?

“It’s very difficult to tell the difference between the flu and Covid, seeing as they are both respiratory illnesses,” says Abbas Kanani, a pharmacist at Chemist Click.

He explains that change in loss or smell is “probably the key to making a guess as to which of the two you may have, as it is more frequent with Covid”. However, a change or loss of smell and taste can also be common with the flu.

It is also more common for those who have picked up Covid to have symptoms that last even after the infection has cleared, which is known as long Covid. Mr Kanani said the only way to be certain as to whether you have Covid or flu is by testing.

This is echoed by Martin Michaelis, professor of molecular medicine at the University of Kent, who says that we “cannot not know for certain which winter bug somebody has” unless they test. He notes that the vast majority of respiratory illnesses or common colds are caused by viruses.

Rhinoviruses are most common, followed by coronaviruses (other than SARS-CoV-2, which causes Covid), adenoviruses, and enteroviruses. In total, more than 200 different viruses are known to cause common cold-like diseases, he adds.

Prof Michaelis explains that all these viruses cause very similar symptoms, including sore throat, runny nose, nasal congestion, sneezing and a cough. People may also experience fatigue, headache, muscle ache, and loss of appetite. Occasionally, patients may develop fever, particularly children. Covid and flu can both also cause severe infection that requires hospital treatment.

What is the difference between flu and Covid?

Flu is a contagious respiratory illness caused by influenza viruses. Flu symptoms, according to the NHS, come on very quickly and can include:

• a sudden high temperature
• an aching body
• feeling tired or exhausted
• a dry cough
• a sore throat
• a headache
• difficulty sleeping
• loss of appetite
• diarrhoea or tummy pain
• feeling sick and being sick

The symptoms are similar for children, but they can also get pain in their ear and appear less active.

Covid is an infectious disease caused by the SARS-CoV-2 virus. The NHS notes that the symptoms of Covid are very similar to symptoms of other illnesses, such as colds and flu.

According to the NHS, the latest symptoms of Covid in adults can include:

• a high temperature or shivering (chills) – a high temperature means you feel hot to touch on your chest or back (you do not need to measure your temperature)
• a new, continuous cough – this means coughing a lot for more than an hour, or three or more coughing episodes in 24 hours
• a loss or change to your sense of smell or taste
• shortness of breath
• feeling tired or exhausted
• an aching body
• a headache
• a sore throat
• a blocked or runny nose
• loss of appetite
• diarrhoea
• feeling sick or being sick

The only way to know for sure is to test

Prof Michaelis says the symptoms caused by different respiratory viruses are “very similar”, but this is “not a surprise” as many of the symptoms “are caused by our own body’s immune response”.

Like Mr Kanani, Prof Michaelis maintains that “if you want to know for certain what you are infected with, you will need a test”.