Refresher: Covid-19 vs flu vs allergies – how to tell the difference

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  • With winter upon us, we may wonder whether our symptoms are caused by allergies, the flu or Covid-19
  • Certain symptoms overlap, although there are some distinct differences that may tell them apart
  • The best way to know for certain what may be causing your illness or discomfort is to undergo a Covid test

These days we find ourselves questioning whether every sniffle, cough, or sneeze is a symptom of an allergy, the flu, or Covid-19.

The new coronavirus, the flu, and seasonal allergies have certain symptoms that can overlap and cause confusion. Earlier last year, Professor Jonny Peter, head of the University of Cape Town (UCT) Lung Institute's Allergy and Immunology Unit, told Health24 that while symptoms of Covid-19 are similar to those of the flu, it might be easier to rule out allergies.

Ideally, one should have a test to confirm which condition one has since respiratory illnesses (like Covid-19 and influenza) have similar symptoms. And while rare, evidence has emerged that people can actually get infected with the flu and Covid-19 at the same time.

Therefore, although you won't know for sure without a test, there are some clues that may help you to differentiate between the three.

Covid-19 and the flu: similarities

Both viruses cause contagious respiratory illnesses, although Covid-19 appears to spread more easily than the flu. 

According to the US Centers for Disease Control and Prevention (CDC), common symptoms that both viruses share include:

  • Fever 
  • Cough 
  • Shortness of breath or difficulty breathing 
  • Fatigue 
  • Sore throat 
  • Runny or stuffy nose 
  • Muscle pain or body aches
  • Headache
  • Vomiting
  • Diarrhoea

It is important to bear in mind that symptoms can vary slightly from person to person. The one symptom that may help one to distinguish between the two diseases is that many Covid victims suddenly lose their sense of smell (anosmia). One study found that 87% of people infected with Covid had anosmia. 

Some Covid sufferers have also reported redness or blisters on their fingers or toes, known as "Covid toes".  

Allergy symptoms

Winter allergies are triggered by indoor allergens in our homes such as dust mites, mould, and pet dander. The common symptoms are unlike those of Covid or flu infection. They include a runny nose, sneezing, a sore throat, and itchy eyes, according to Harvard Health

“Itching, particularly, is an important one, because it’s not a symptom of the common cold, flu, or coronavirus,” Peter said, adding: “Sneezing is also not a prominent feature of coronavirus and the flu, but common in allergies and the common cold.”

These allergens are present year-round, but may flare up in the winter due to poorly ventilated spaces since we're often cooped up in our homes with the windows closed.  

Guidance by the Icahn School of Medicine at Mount Sinai explains that, generally, the key differentiating factors between Covid infection and allergies are fever and body aches (malaise), where, typically, either of these symptoms are not seen in allergy sufferers. Mild fatigue may occur in the case of allergies, but the fatigue seen with Covid-19 is more extreme.

Peter also simplified it by explaining that allergic triggers will predominantly affect your nose and eyes, whereas, with the flu and Covid, your whole body will more likely be affected.

Symptom onset

If you have been exposed to the flu, typically, you would experience symptoms anywhere from one to four days after infection. With Covid, you would experience symptoms around five days after exposure to the virus, but symptoms can appear two to 14 days after infection, notes the CDC

With these two illnesses, the onset of symptoms generally resolves within a short period (symptoms may worsen and recovery be prolonged if a high-risk individual catches the virus). On the other hand, allergy-related symptoms will often be consistent, said Peter. This means you’ll have persistent sneezing, a runny nose, and itchy eyes, for example, that will be ongoing until you get treatment, or the allergen is removed. 

Image: Health24

Remember, there’s no reliable way to distinguish between symptoms of the flu and Covid, so if you are experiencing symptoms that you think may be Covid-19, the only way to know for certain is to have a test. 

Get the flu shot

South Africa sees around 47 000 flu cases and close to 12 000 flu-related deaths annually, with around 50% of cases being severe and requiring hospitalisation, Health24 recently reported

Flu infections are expected to resurge this year in the absence of strict non-pharmaceutical interventions (NPIs), Dr Thinus Marais, Medical Head, Sanofi Pasteur, recently said.

Not only will getting the flu shot potentially prevent co-infection of the flu and Covid, but it may reduce the burden of flu-related hospitalisations on the healthcare system.

The quadrivalent influenza vaccine (QIV) is widely available in South Africa at major pharmacy chains including Clicks, Dis-Chem, and Shoprite (via MediRite pharmacies). All three groups accept major medical aids. 

The National Institute of Communicable Diseases (NICD) recommends that the flu vaccine and Covid-19 vaccine be given at least 14 days apart.

*For more Covid-19 research, science and news, click here. You can also sign up for our Daily Dose newsletter here.

READ | Four important reasons why you should get the 2021 flu shot

READ | Covid nails: These changes to your fingernails may show you’ve had coronavirus

READ | Fighting the flu season: Two experts answer key questions about the flu shot

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