As with many infections, the effect COVID-19 has on your health can vary a lot. Some people get no symptoms at all, while degrees of illness can range from mild or moderate to severe or critical – sometimes leading to hospitalisation and death.
There are many things that increase or reduce your risk of getting severe COVID-19. So what do the terms mild, moderate and severe COVID-19 actually mean, and how likely are you to get them? Read on to learn more, including how variants and vaccines can affect the different degrees of COVID-19 illness.
Virus variants can change the severity of symptoms
With COVID-19 affecting every country in the world, new ‘variants’ of the virus continue to appear. These variants sometimes go on to become the main or ‘dominant’ virus in circulation.
Every time a new variant appears, scientists need to check how the virus has changed, what symptoms it causes and how ill it makes people, and whether vaccines need updating as a result.
For example, there’s some evidence that the Omicron variant is more likely than the previously dominant Delta variant to cause mild COVID-19. Although serious illness and death can still happen.
Vaccinations dramatically cut the risk of severe COVID-19
Scientific developments since the start of the pandemic mean the risk of severe COVID-19 can be reduced in 2 key ways.
COVID-19 vaccines can dramatically reduce your risk of both getting symptomatic COVID-19 and developing severe COVID-19 that needs hospital treatment.
The latest evidence suggests that, for the Delta variant, a 3rd ‘booster’ dose of vaccine gives more than 90% protection against symptomatic COVID-19 and up to 99% against being hospitalised. For the Omicron variant, the booster offers up to 70% protection against developing symptoms, and up to 95% against hospitalisation.
Antiviral and antibody treatments are now also available to treat symptoms. In the UK, these are offered to people with COVID-19 who have a high risk of developing severe COVID-19.
What are the symptoms of COVID-19 in order of severity?
Having asymptomatic COVID-19 means that you have no symptoms – so unless you take a test, you won’t know you have it. Research suggests that up to 1 in 3 people who have COVID-19 may be asymptomatic.
It’s possible for anyone to have asymptomatic COVID-19, although studies suggest that children and healthy young adults seem to be most likely to have no symptoms at all.
It’s also possible that you may not be truly asymptomatic. You may ignore very mild symptoms, such as a runny nose or tiredness, because you don’t feel unwell or think you just have a cold.
Even if you have asymptomatic COVID-19, you can still infect other people. So it’s a good idea to test yourself regularly – and especially if you’ve been in contact with someone who has COVID-19 – to help protect yourself and others.
The majority of people who get COVID-19 have a mild illness and don’t need any specific treatment or hospitalisation. You should be able to manage your symptoms at home.
If you have mild COVID-19 you’ll have 1 or more of the common symptoms listed below, and won’t have breathing problems or shortness of breath.
Common signs and symptoms of COVID-19, which can be caused by both the Delta and Omicron variants, include:
- high temperature (fever)
- loss of sense of smell and/or taste
- sore throat
- tiredness (fatigue)
- muscle aches and pains
- feeling sick (nausea)
- being sick (vomiting)
- looser or more frequent poos (diarrhoea)
See below for what we know so far about the possible differences in Omicron severity and symptoms.
With mild COVID-19, symptoms usually last about 7 to 14 days. However, even mild COVID-19 can sometimes make you feel quite unwell, and it may take some time before you feel fully back to normal.
When to see a doctor if you have mild COVID-19
If you’re at high risk of becoming seriously ill from COVID-19 – due to a health condition or a weakened immune system, for example – you should speak to a doctor as soon as you test positive, even if you think you have mild COVID-19. This is because you may be able to have antiviral or antibody medication to help with your symptoms and reduce your risk of developing severe COVID-19 – and these have been shown to work best when taken as soon as possible (ideally within 5 days). Your doctor can confirm if you’re eligible for these treatments.
You should also see a doctor if you notice shortness of breath that’s getting worse or doesn’t improve over time, as you may have progressed from mild COVID-19 to a more severe stage of illness. Some people are at higher risk of this (see below for details).
Sometimes, COVID-19 symptoms can last for many weeks or months after you’re infected, even if you have mild illness – this is known as long COVID. So if you're not recovering after 4 weeks, you should also see your doctor.
The signs and symptoms of moderate COVID-19 are generally the same as for mild illness. The difference is that these symptoms can be worse, and you’ll have more difficulty breathing than normal – such as noticing shortness of breath when you’re moving around.
In most cases, moderate COVID-19 doesn’t require any treatment and will usually gradually settle over a few weeks.
When to see a doctor if you have moderate COVID-19
The reasons for seeing a doctor with moderate COVID-19 are similar to those for mild illness (if you’re at high risk of becoming seriously ill, you notice worsening shortness of breath, or you still have symptoms after 4 weeks).
If you visit a doctor, they’re likely to find signs of a chest infection lower down in your lungs, and a chest X-ray may look abnormal. (In mild cases, no changes would be seen on a chest X-ray.)
They’ll usually also check the level of oxygen in your blood, to see how well you’re breathing, using a device called a pulse oximeter. In moderate COVID-19, the reading won’t be dangerously low.
Severe COVID-19 needs to be diagnosed by a doctor, through an examination and tests.
It causes inflammation of your lungs, known as pneumonia. The inflammation happens deep in your lungs, in their tiny air sacs (alveoli), which means they get less air and don’t work as well.
If you have severe COVID-19 you’ll usually need to be treated in hospital.
When to call the emergency services if you have severe COVID-19
If you have signs of severe COVID-19, you should call for emergency medical help. These signs include:
- a blood oxygen level of less than 94% – measured by a pulse oximeter, as above
- difficulty breathing – including fast or shallow breathing
- trouble speaking normally
- chest discomfort
Treatment of severe COVID-19 in hospital may include:
- oxygen treatment
- antiviral medication
- steroid medication – to help reduce inflammation and prevent an overactive immune system
- treatment for other infections – for example, antibiotics for a bacterial infection
Who is more at risk of severe COVID-19?
You’re more at risk of severe COVID-19 if:
- you’re unvaccinated
- you’re older – particularly if you’re over 65
- you smoke
- you’re overweight or obese
- you have a weakened immune system (immunocompromised)
- you have certain health conditions, including:
- heart, kidney, liver or lung disease
- Down’s syndrome
- sickle cell disease
- stroke or cerebrovascular disease
- mental health conditions such as depression and schizophrenia
If you have more than 1 health condition, your risk increases further.
Research in the UK also suggests you may be at greater risk of becoming seriously ill from COVID-19 if you’re of Black, Asian or minority ethnic origin.
This is the most serious form of COVID-19, which usually requires treatment in a hospital intensive care unit.
With critical COVID-19, you’re extremely ill and can have breathing (respiratory) failure, septic shock (due to blood poisoning) and organ failure, where organs such as your kidneys and liver stop working.
Treatment for critical COVID-19 is similar to treatment for severe COVID-19, but may also involve:
- breathing support such as a mechanical ventilator
- treatments that help support any organs that may be failing
Knowledge about how to effectively treat critical COVID-19 has come a long way since the start of the pandemic. But in some serious cases, it can still be fatal.
Critical COVID-19 appears to have similar risk factors as severe COVID-19. Research shows that, along with being unvaccinated, older age, smoking, diabetes, high blood pressure, cancer and heart, kidney and lung diseases are all associated with worsening illness in people admitted to hospital with COVID-19.
How likely am I to get critical COVID-19?
Fortunately, most people who get COVID-19 don’t go on to develop critical illness or long-term problems.
All the research shows that your age plays a big role in predicting whether you’ll get very ill with COVID-19, and your risk of critical illness increases sharply with increasing age. According to the US Centers for Disease Control and Prevention, more than 81% of COVID-19 deaths happen in people over 65.
The health conditions mentioned above can increase your risk, too. And the more conditions you have, the greater the risk.
Evidence also suggests that men are more likely to die from COVID-19 than women, regardless of age. This could be partly because men may be more likely to have other health conditions.
Finally, pregnancy has been shown to increase your risk of critical COVID-19. A review of nearly 200 studies found pregnant or recently pregnant women are more likely to be admitted to intensive care with COVID-19 than non-pregnant women of reproductive age. Getting COVID-19 when you’re pregnant also increases your risk of giving birth prematurely.
Omicron: severity and symptoms
In many countries, including the UK, the Omicron variant became the dominant virus in circulation in late 2021 (taking over from the Delta variant). Here’s what you need to know:
- evidence so far suggests Omicron is more likely than Delta to cause mild COVID-19, and cold-like symptoms such as a runny nose, sore throat and headache are more commonly reported. Data suggests that you have a lower risk of being hospitalised if you’re infected – particularly if you’re fully vaccinated
- it spreads more easily (is more infectious) than previous variants. So it’s still important to take steps to avoid getting or spreading it – such as regular hand washing, wearing a face covering and avoiding crowded places where possible
- as with all variants, you can spread the virus even if you don’t have symptoms and/or have been vaccinated. So it’s a good idea to do regular tests (such as lateral flow tests)
- research shows COVID-19 booster jabs provide good protection against Omicron. However, 2 doses aren’t as effective – so it’s important to get your booster to raise your antibodies and maximise your protection against severe COVID-19
Guidelines about COVID-19 and virus variants will change as we learn more, so check the latest UK government advice.
Your health questions answered
Will new variants of COVID-19 be less likely to cause severe illness?
Answered by: Dr Roger Henderson
“The short answer is that nobody knows and we have to wait and see. Although new variants will continue to develop, their impact will depend on whether their random genetic variations make them more or less dangerous to us. However, the development of vaccines that give significant protection against coronavirus, including new variants, means we’re now in a much better position to protect ourselves against serious illness if we’re fully vaccinated.”
Does the severity of COVID-19 affect whether or not you get long COVID?
Answered by: Dr Roger Henderson
“You can develop long COVID even if you weren’t particularly unwell when you were first infected, or even after having asymptomatic COVID-19. But a recent study that looked at more than 200,000 people who’d had COVID-19 found that those with more severe illness had a higher risk of having more long COVID symptoms. They were also more likely to have thinking (cognitive) symptoms, such as ‘brain fog’. However, they weren’t as likely to have symptoms such as headaches and muscle pains, so these symptoms might not be affected by the severity of your initial illness.”