Flu vs COVID: How Can You Tell the Difference?

Flu and COVID 19 share a lot of symptoms. That overlap makes it genuinely hard to tell them apart just by how you feel, and even experienced clinicians can struggle to distinguish between them without testing.

Here’s what the evidence says about the differences, and why testing is the only way to know for sure.

Symptoms They Share

Both illnesses commonly cause:

• Fever
• Cough
• Fatigue
• Sore throat
• Headache
• Muscle aches
• Runny or blocked nose
  
  

Because of this overlap, symptoms alone usually can’t tell you which one you have. This is true even when you compare the full list of symptoms someone is experiencing, not just one or two in isolation.

Subtle Differences Worth Knowing

Loss of taste or smell

This is more strongly associated with COVID 19, especially with earlier variants of the virus. It’s less common with flu, though not unheard of. Newer COVID variants cause this less often than they used to, so its absence doesn’t rule COVID out, and its presence doesn’t guarantee it’s COVID rather than something else.

Speed of onset

Flu symptoms often come on suddenly. Many people can say almost exactly when they started feeling ill, sometimes down to the hour. COVID symptoms more often build up gradually over a day or two. This isn’t a hard rule, just a general pattern that clinicians sometimes look for, and plenty of exceptions exist in both directions.

Digestive symptoms

Nausea, vomiting, or diarrhoea appear somewhat more often with flu, particularly in children, though these symptoms can occur with COVID as well.

Why You Usually Can’t Tell From Symptoms Alone

Even doctors can’t reliably distinguish flu from COVID 19 based on symptoms in a clinical exam. The overlap is simply too large for symptoms alone to be a dependable guide. Testing is the only reliable way to know which one you have, and this matters, because:

• Treatment options differ. Antivirals for flu and COVID work differently, and aren’t interchangeable
• Isolation and precaution advice may differ depending on which illness you have
• Some people are eligible for specific antiviral treatment for one illness but not the other, particularly those in higher risk groups

What to Do If You’re Unsure

• If you have a home test available, use it
• If you’re in a high risk group, such as being over sixty five, pregnant, or living with an underlying health condition, contact your GP or NHS 111. You may be eligible for specific treatment
• Rest, stay hydrated, and monitor your symptoms either way
• Seek urgent medical help if you develop breathlessness, chest pain, confusion, or your symptoms rapidly worsen

The Best Protection: Vaccination for Both

Since you can’t easily tell them apart, and both can cause serious illness, the most effective protection is getting vaccinated against both flu and COVID 19 each autumn, if you’re in an eligible group. Many pharmacies can now give both vaccines in the same appointment, which makes staying protected against both illnesses considerably more convenient than it used to be. Vaccination doesn’t guarantee you won’t catch either illness, but it substantially reduces the chance of severe symptoms and complications, particularly in higher risk groups.

This article is for general information only. It’s not personal medical advice. If you’re feeling unwell and unsure what you have, or you’re in a high risk group, please contact your GP, NHS 111, or your local pharmacy for advice.