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COVID-19 is an infectious disease caused by a virus that was first identified in December 2019 in Wuhan, China. This leaflet deals with the symptoms, causes and treatment of COVID-19.

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What is COVID-19?

COVID-19 is an infectious disease caused by a virus (SARS CoV-2). COVID-19 is short for "coronavirus disease 2019", because the disease was first identified in December 2019.

COVID-19 was first discovered in Wuhan, China, and rapidly spread throughout the world during 2020, causing the COVID-19 pandemic. COVID can cause illness ranging from mild symptoms (or no symptoms), to severe disease requiring hospital treatment, to death.

What are the symptoms of COVID?

The symptoms of COVID-19 can include:

Many of these symptoms are similar to those of mild viral infections including colds and flu.

In serious cases, COVID can cause:

  • Severe breathlessness - for example, feeling very short of breath whilst resting, being too breathless to talk, or becoming very breathless when moving a short distance.

  • Chest pain.

  • Coughing up blood.

  • New or worsening confusion.

  • Drowsiness.

How long does it take for COVID symptoms to show?

The average time between being infected with COVID-19 and showing symptoms has been estimated at about 4-6 days, although it has taken from 2-18 days in some cases.

How long does COVID last?

Most people with mild COVID infections feel better within one or two weeks after developing the infection. Much like any other viral infections, it is normal for the cough to take up to three weeks to disappear entirely. People who have been seriously ill - for example, people who needed to stay in hospital or intensive care - are likely to take longer to recover.

Some people have symptoms that last for weeks, months, or years after catching COVID. See the long COVID leaflet for more information.

How long are you contagious with COVID?

Most people will no longer be contagious at five days after developing symptoms of COVID. Some people can be contagious up to 10 days after developing COVID and people who have been seriously ill, or have weak immune systems, may be contagious for even longer. Children and young people tend to be contagious for shorter periods of time.

Most countries have advice or rules about isolation and staying at home, with the aim of reducing the spread of COVID. In the UK, in November 2022, the national guidance was that adults with COVID should:

  • Stay at home and avoid contact with other people for five days, counting from the day after a positive COVID test was taken.

  • Avoid contact with anyone who would be at high risk of becoming severely unwell with COVID, including people with a weakened immune system, for 10 days.

Children or young people with COVID have been advised to stay at home and avoid contact with other people for three days.

In the USA in November 2022, the Centers for Disease Control and Prevention (CDC) advised that people with COVID-19 should:

  • Stay at home and avoid contact with others for five days (counting from the day after a positive COVID test was taken).

  • End isolation if their symptoms are improving after five days and have been fever-free for 24 hours.

  • Continue to isolate if their symptoms are not improving at five days, until their symptoms are improving and they have been fever-free for 24 hours.

  • Isolate for 10 days if they have had moderately severe COVID (causing shortness of breath or difficulty breathing).

  • Isolate for at least 10 days, consult a doctor, and consider taking a viral test before ending isolation for people who needed hospital treatment for COVID, or people who have weakened immune systems.

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How can you test for COVID-19?

There are two main types of COVID-19 tests. In both cases, these are done using nose or throat swabs to pick up virus particles. The tests are:

  • 'Lateral flow' or 'rapid tests'. These can be done at home, by using a small plastic dropper to put a sample of the test solution into a plastic cassette. These give a result within about 15 minutes to 30 minutes depending on the type of test. A positive test is a good indicator of COVID-19 infection. It's possible to have COVID-19 and still get a negative result - one estimate is that about a third of people with symptomatic COVID-19 infection, confirmed via a PCR test, will have a negative lateral flow test.

  • PCR tests. These need to be sent to a laboratory, which uses special lab equipment to perform the test. These usually take at least a day to return a result. PCR tests are more sensitive for COVID-19 infection, ie people who have COVID-19 are less likely to get a false negative PCR test.

Neither test can tell the difference between 'live' virus, which is able to infect other people and cause illness, and 'dead' virus, which is harmless; particularly with PCR tests, which may remain positive for several weeks after the infection has resolved and is no longer contagious.

In the UK, only a small number of people are currently eligible to get free lateral flow tests from the government; details can be found on the GOV.UK website (see Further Reading). Lateral flow and PCR tests can be bought, and some countries require proof of testing to enter when travelling.

What causes COVID-19?

COVID-19 is caused by a coronavirus, SARS CoV-2. Other types of coronavirus cause different illnesses, from mild ones such as colds, to more serious conditions such as SARS and MERS.

Since the beginning of the pandemic, new variants of the SARS CoV-2 virus have emerged. These are slightly different versions of the virus which behave in different ways. These have tended to be more contagious (spreading more easily) than the original virus did. There is also some concern that existing vaccines and treatments might be less effective against the variants. However, in some cases, they also seem to be less likely to cause serious illness.

Notable variants of SARS CoV-2 include: the alpha variant; beta variant; delta variant; and omicron variant.

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Who is at risk of catching COVID?

Anyone can get COVID-19.

COVID-19 is spread by breathing in virus particles in the air; people who have close contact with lots of other people, particularly in crowded indoor areas with poor ventilation, are more likely to come into contact with the virus. However, anyone can be exposed to COVID-19, especially when rates of infection are high.

Most people have a mild illness that recovers without any medical treatment. However, some people are at higher risk of becoming seriously unwell and dying from COVID-19. Groups of people who have been identified as being at increased risk include:

  • People who are have not had vaccinations against COVID.

  • People aged over 60, with the risk increasing with age.

  • People with type 1 or type 2 diabetes.

  • People who are pregnant.

  • People from certain ethnic groups; for example, in the UK, in the first six months of the COVID-19 pandemic, infection and death rates from COVID were higher in minority ethnic groups, such as Black and Asian ethnicities, than in White ethnicities.

  • People who are overweight or obese.

  • People who smoke.

  • People with other medical conditions, such as COPD, high blood pressure, and serious mental health conditions.

For most people, getting vaccinated against COVID-19 has made the risk of serious illness and death small. However, some people are at particularly high risk from COVID-19 still, such as people with:

How to treat COVID

Vaccines are the most effective way of preventing serious illness and death from COVID-19.

Most people will make a full recovery with time, and do not need any specific treatments unless they develop signs and symptoms of serious illness. Medicines like paracetamol and ibuprofen can be used to treat symptoms like pain and fever.

In the UK, people who are at very high risk of serious COVID-19 disease may be offered specific antiviral treatments (eg nirmaltrevir/ritonavir (Paxlovid®)) if they have tested positive for COVID-19, to reduce the risk of developing serious disease (see Further Reading).

People who become seriously ill with COVID-19, and are admitted to hospital, may be given:

  • Oxygen, if their blood oxygen levels are low.

  • Dexamethasone, a type of steroid medicine, if they are given oxygen.

  • Breathing support if required - either with specialised masks and machines to aid breathing, or, if this is not working or is unsuitable, with a ventilator to pump air into the lungs. People receiving these will usually need to be in special wards: high-dependency units or intensive care.

  • Antiviral treatments, such as remdesivir, nirmatrelvir/ritonavir (Paxlovid®), molnupiravir.

  • Monoclonal antibodies- these are used to help treat autoimmune conditions such as rheumatoid arthritis. In this case- they attack the virus' surface to stop it entering the person's cells. Medications such as casirivimab and imdevimab are mostly used.

Editor’s note

Dr Krishna Vakharia, 21st April 2023

The National Institute for Health and Care Excellence (NICE) has recommended a number of medications to treat COVID-19 depending on the severity.

  • Nirmatrelvir plus ritonavir for treating mild COVID-19.

  • Sotrovimab for treating mild COVID-19.

  • Tocilizumab for treating severe COVID-19.

These medications will only be offered by specialists under certain conditions and if the criteria for prescribing are met.

Dr Krishna Vakharia, 14th May 2024

NICE has recommended another medication, remdesivir, that can be used in hospitals under certain conditions for babies as well as adults. If you are eligible, your doctors will discuss this with you. (See further reading)

Other treatments have been promoted for use in COVID-19, such as hydroxychloroquine and ivermectin. The best available evidence shows that these drugs are not effective at treating COVID-19, and may cause harm.

COVID complications

The main cause of death in severe COVID-19 infection is respiratory failure.

Other complications of COVID-19 include:

How to prevent COVID

The best way to prevent becoming seriously ill with COVID is by getting vaccinated against it.

COVID vaccines may reduce the risk of catching COVID, and the risk of passing it on to other people, but do not fully prevent these from happening. However, they do significantly reduce the risk of developing serious illness or dying from COVID-19.

COVID is spread by close contact with people who have the virus. People with COVID-19 infection release virus particles into the air and on to nearby surfaces when breathing, coughing, or sneezing.

Ways to reduce the risk of catching COVID include:

  • Getting vaccinated against COVID-19.

  • Meeting other people outside, if possible.

  • Ensuring indoor areas are well ventilated when meeting other people inside - eg opening windows and doors to let in fresh air.

  • Avoiding crowded places, especially if they are poorly ventilated.

  • Wearing a face covering or face mask.

  • Washing your hands with soap and water, or hand sanitiser, regularly.

  • Avoiding touching your mouth, nose, or eyes without washing your hands first.

  • Reducing the spread to others by isolating if you have COVID-19.

  • Following any other local public health guidance.

Editor’s note

Dr Krishna Vakharia, 16th October 2023

Government guidance from September 2023 advises that if you feel unwell, you should wait until you recover to get a vaccine.

There is now no need to wait 4 weeks after having had COVID-19, provided you are well. You should not attend a vaccine appointment if you think you could be infectious to others.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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