Flu comes on quicker, but COVID-19 is more infectious – and that’s not all.
Medically reviewed by Dr Roger Henderson and words by Annie Hayes
‘Could it be COVID-19?’ is a question many Brits will be asking themselves at the first sign of a sniffle this winter. The good news is, even though coronaviruses share similar symptoms with the flu, there are some key differences between them.
With cold and flu season fast-approaching, we asked Professor Sam Shah, chief medical strategy officer at Numan, to talk us through the key similarities and differences between your typical bout of influenza and COVID-19:
difference between flu and COVID-19
What’s the difference between flu and COVID-19?
COVID-19 and flu are both contagious respiratory illnesses, which means they affect your lungs and breathing, and can be spread to others. However, they are caused by different viruses.
COVID-19 and flu are both contagious respiratory illnesses, which means they affect your lungs and breathing.
COVID-19 is caused by infection from a coronavirus called SARS-CoV-2, while and flu is caused by infection with an influenza virus, of which many strains exist. Much is still unknown about COVID-19 and the virus that causes it.
Flu vs COVID-19: symptoms
Symptoms of both COVID-19 and flu can range from mild to severe, and both can cause pneumonia. The World Health Organisation (WHO) classifies a ‘mild’ case as one where the patient does not require hospitalisation.
Because COVID-19 and flu share some of the same symptoms, testing may be needed to confirm a diagnosis. Common symptoms include:
- Shortness of breath
- Runny nose
- Nasal congestion
- Loss of appetite
- Sore throat
- Muscle pain or body aches
- New loss of taste or smell
The key to telling the difference between them is by which symptoms are predominant. The main symptoms for COVID-19 are a high temperature, a new, continuous cough, and a loss or change to your sense of smell or taste. Meanwhile, influenza can feel like a common cold when it starts, with symptoms such as a runny nose, nasal congestion and sore throat initially but then other symptoms quickly develop such as a high temperature, widespread (and often significant ) aches and pains, and profound tiredness and fatigue.
There are also differences in the time between exposure and the onset of symptoms. A person typically develops COVID-19 five days after they are infected, but symptoms can appear as quickly as two days or as long as 14. ‘Flu symptoms usually begin about two days after exposure, but can take up to four days,’ says Shah.
Flu vs COVID-19: transmission
Both the flu and COVID-19 are spread in similar ways – through contact and respiratory droplets, for example sneezing, coughing, or talking, says Shah. These tiny droplets can land in the mouths or noses of people nearby, or may linger in the air and be inhaled into the lungs.
A person can also become infected by direct physical human contact, for example shaking hands. It’s also possible to contract viruses by touching a surface or object that has the virus on it, and then touching the mouth, nose or eyes with the same hand.
While both COVID-19 and flu are contagious, the latest evidence suggests COVID-19 is much more contagious and spreads more rapidly than the flu. It also more typically spreads from adults to children – unlike flu, where transmission from children to adults is common.
People can spread COVID-19 for around two days before they start experiencing symptoms – and even if symptoms go away, they may remain contagious. ‘Most people with COVID19 can be infectious for about 10 days, so it’s important they self-isolate for 14 days to avoid spreading the virus,’ says Shah.
People with the flu, meanwhile, are generally contagious one day before their symptoms start ‘and usually up to a week later, but can be contagious until their symptoms disappear,’ says Shah.
Flu vs COVID-19: high risk groups
Those most at risk for severe flu infection are children, pregnant women, the elderly, people with long term health conditions, and people with a weakened immune system, according to the WHO. Similarly, older age and underlying health conditions (including among infants and children) increase the risk for severe COVID-19 infection.
‘People who may be immunocompromised or those suffering from severe illness are at high risk for COVID19 – or example, those receiving intense radiotherapy or targeted cancer treatment, people who have had an organ transplant, or people with conditions that mean they are at high risk of infection,’ says Shah.
Others may have conditions that place them at moderate risk of contracting COVID-19, he continues, such as people with diabetes, heart disease or lung conditions. ‘If you are at higher risk of coronavirus, you will also be more at risk from flu,’ Shah adds.
Flu vs COVID-19: complications
While both COVID-19 and flu can result in moderate to serious complications, COVID-19 is the deadlier of the two, and is more likely to result in severe illness or death.
While both COVID-19 and flu can cause complications, COVID-19 is more likely to result in severe illness or death.
Around 15 per cent of cases are severe, according to the WHO, and approximately 5 per cent are critical, which refers to people who require a ventilator to breathe.
Complications associated with both COVID-19 and flu include:
- Respiratory failure
- Acute respiratory distress syndrome
- Cardiac events (such as heart attack and stroke)
- Multiple organ failure
- Inflammation of the heart, brain or muscle tissues
- Worsening of chronic medical conditions
- Secondary bacterial infections
Additional complications for COVID-19 include blood clots in veins and arteries, and Multisystem Inflammatory Syndrome in Children (MIS-C). Additional complications for the flu include sinus and ear infections.
Flu vs COVID-19: treatment
Most people with COVID-19 or flu do not require medical treatment. For people with flu, doctors sometimes prescribe an antiviral drugs, which helps the body fight off the virus and reduces the duration of the illness. There are currently no antiviral drugs or any other medical treatments approved to treat COVID-19.
General advice for easing COVID-19 and flu symptoms include:
- Get plenty of rest and stay hydrated
- Take paracetamol or ibuprofen to ease fever and muscle aches
- Avoid lying on your back if you have a cough
Flu vs COVID-19: prevention
The most effective way of preventing the flu is by getting the flu jab each year. Flu strains vary from season to season, so doctors predict which strains will be prevalent and create the vaccine accordingly. Unfortunately, there is currently no vaccine available for SARS-CoV-2, the virus strain that causes COVID-19. Currently, the most effective way to prevent COVID-19 is to practice social distancing.
‘Avoiding close contact with people you don’t live with, regularly washing your hands, and wearing a face mask helps reduce the spread of COVID-19,’ says Shah. ‘Effective flu prevention includes avoiding close contact with people who are sick, staying home when sick, covering your mouth and nose, and washing your hands.’