Difference between COVID and Flu

COVID-19 and flu (influenza) are both contagious respiratory illnesses that can produce strikingly similar symptoms, which is exactly why they're so often confused with one another. They're caused by entirely different viruses, though. Understanding the differences matters for how each is prevented, tested for and treated.

Different viruses, similar symptoms

COVID-19 is caused by SARS-CoV-2, first identified in December 2019, while flu is caused by influenza viruses that circulate every year, typically peaking through the winter months in the UK. Despite the different viruses, the two illnesses can look very alike day to day, with symptoms including fever, cough, sore throat, fatigue, body aches and headache common to both.

Symptoms more specific to COVID-19

Some symptoms are more strongly associated with COVID-19 than with flu, most notably a new loss or change to your sense of smell or taste. This symptom is far less common with flu and can be a useful, if imperfect, clue when trying to work out which illness you're dealing with. That said, symptom overlap is significant enough that testing is the only reliable way to know for certain.

Differences in severity

Generally speaking, COVID-19 has carried a higher risk of severe illness, hospitalisation and death than a typical seasonal flu, particularly in unvaccinated people and during the earlier waves of the pandemic before broad immunity had built up. That gap has narrowed over time thanks to vaccination and increased population immunity from prior infection, but COVID-19 has continued to pose a somewhat greater risk on average, especially to older adults and people with underlying health conditions.

Differences in transmission

Both illnesses spread mainly through respiratory droplets released when an infected person coughs, sneezes or talks nearby and both can also spread via contaminated surfaces, though this is a secondary route for each. COVID-19 has generally proven more transmissible than seasonal flu, spreading more easily between people, including from those who have no symptoms at all, which is part of why it proved so difficult to contain in the early stages of the pandemic.

Complications

Both illnesses can lead to pneumonia in more severe cases. COVID-19 is also associated with long COVID, a set of symptoms including fatigue and breathlessness that can persist for months, a phenomenon that appears to be both more common and, on average, more prolonged than the lingering after-effects sometimes reported following flu.

Prevention and vaccination

Both illnesses are preventable, at least in part, through vaccination. Flu vaccines are updated and offered annually in the UK, generally in fitting with a specific eligible groups, ahead of the winter season. COVID-19 vaccination programmes have similarly evolved into a pattern of periodic updated doses for eligible groups, including older adults, healthcare workers and people with certain health conditions. General prevention measures, good hand hygiene, staying home when unwell and improving ventilation indoors, help reduce the spread of both.

Treatment

Treatment for both illnesses is largely similar for mild cases: rest, fluids and over-the-counter medication to manage fever and aches. Antiviral medicines exist for both flu and COVID-19, generally reserved for people at higher risk of severe illness and are most effective when started early in the illness. Severe cases of either illness may require hospital treatment.

Why it's worth knowing which one you have

Because treatment options, isolation advice and risk to others can differ, testing is genuinely useful when it matters, for instance if you're at higher risk yourself, or planning to be around someone who is. If you develop flu-like or COVID-like symptoms and you're unsure what to do next, NHS 111 can offer guidance suited to your specific situation.

COVID-19, flu and the common cold at a glance

Feature	COVID-19	Flu	Common cold
Onset	Gradual to sudden	Sudden	Gradual
Fever	Common	Common, often high	Rare
Loss of smell or taste	Fairly common	Uncommon	Rare
Typical severity	Mild to severe	Mild to severe	Mild
Vaccine available	Yes	Yes	No

This is a general guide rather than a diagnostic tool. Individual cases vary considerably and testing remains the only reliable way to confirm which illness you actually have.

Can you have both at once?

Yes, it's possible to be infected with both COVID-19 and flu at the same time, sometimes informally referred to as a "twindemic" scenario at the population level, or "flurona" for an individual co-infection. This tends to be more likely during winter months when both viruses circulate simultaneously. Having both at once can potentially lead to a more severe illness than either alone, which is part of why health authorities encourage eligible people to take up both COVID-19 and flu vaccinations where recommended.

Frequently asked questions

Can one test tell you if you have COVID-19 or flu?

Combined tests that check for both COVID-19 and flu from a single swab do exist and are increasingly available, including in some NHS and pharmacy settings, though standard home lateral flow tests typically only check for one or the other.

Do the same precautions protect against both?

Largely, yes. Good hand hygiene, staying home when unwell, covering coughs and sneezes and improving indoor ventilation all help reduce the spread of both illnesses.

Is it worth getting both vaccines in the same appointment?

Many GP surgeries and pharmacies now offer COVID-19 and flu vaccines together during the autumn booster season, which studies have found to be safe and convenient for eligible patients.

When to get tested for which

If you develop symptoms and want to know whether it's COVID-19 or flu, testing is generally worth doing if you're in a higher-risk group, if you're planning to be around someone vulnerable, or if knowing which illness you have would change how you manage it, for example if you might be eligible for antiviral treatment. Home lateral flow tests for COVID-19 are widely available from pharmacies and combined tests that check for both COVID-19 and flu are increasingly available too.

If you're otherwise healthy and not planning to be around anyone vulnerable, testing is less essential, since the advice in either case is broadly similar: rest, stay hydrated and stay away from others until you're feeling better. If your symptoms are severe or don't improve as expected, it's worth speaking to your GP or NHS 111 regardless of which specific illness you have.

Historical context: how flu pandemics have been handled

Flu pandemics are not new and the world has faced several over the past century, including the 1918, 1957, 1968 and 2009 pandemics. Each prompted public health responses appropriate to the medical understanding and technology of the time. Comparing how COVID-19 was managed with how these earlier flu pandemics were handled shows just how far vaccine development, genomic surveillance and international coordination have advanced, even though many of the same fundamental challenges, including balancing public health measures against economic and social disruption, remain strikingly similar.

A note on other winter viruses

COVID-19 and flu aren't the only respiratory viruses that circulate during the colder months. RSV (respiratory syncytial virus) and various common cold viruses also spread widely each winter, adding to the general burden of respiratory illness on both individuals and the NHS. Many of the same precautions, good hand hygiene, staying home when unwell and improving ventilation, help reduce the spread of all of these viruses, not just COVID-19 and flu specifically.