Overview
COVID-19 is an illness caused by the SARS-CoV-2 coronavirus. It spreads mainly through the air between people who are close to each other, especially in crowded indoor spaces with poor ventilation.
WHO states that most people make a full recovery without needing treatment. The illness still matters because it can be severe in older adults and people with other health conditions, and because a minority of people develop symptoms that last for months.
Disease Summary
- Category
- Infectious Disease
- Cause
- SARS-CoV-2 coronavirus
- Transmission
- Airborne respiratory particles
- Body System
- Respiratory System
- Preventable
- Yes
- Curable
- Yes
Symptoms
Common Symptoms
Most people with COVID-19 experience one or more of the following symptoms.
Fever or Chills
Listed first by CDC among the symptoms of COVID-19 and among the most common symptoms in current WHO guidance.
Cough
The cough can be dry and may persist for some time after the rest of the illness has settled.
Sore Throat
WHO names sore throat among the most prevalent symptoms of currently circulating variants.
Fatigue
Tiredness that is out of proportion to activity is common and can last longer than the fever.
Headache and Body Aches
Both WHO and CDC list headache along with muscle and body aches.
Congestion or Runny Nose
Upper airway symptoms are common and overlap almost completely with a cold.
Loss of Taste or Smell
CDC notes this has become less common since the Omicron variants but still occurs.
Nausea, Vomiting or Diarrhoea
CDC notes that stomach symptoms occur and may appear before any breathing symptoms.
Danger Signs
Seek urgent medical attention immediately if any of the following symptoms develop.
Trouble Breathing
CDC lists this first among emergency warning signs. WHO adds being unable to speak in full sentences at rest.
Persistent Chest Pain or Pressure
Chest pain or pressure that does not go away is an emergency warning sign.
New Confusion
A change in thinking or alertness in someone with COVID-19 needs emergency assessment.
Inability to Wake or Stay Awake
Difficulty rousing a person is listed by CDC as an emergency warning sign.
Pale, Grey or Blue Skin, Lips or Nail Beds
This indicates the blood is not carrying enough oxygen. The colour change depends on skin tone, so check lips, gums and nail beds.
Diagnosis
Symptoms and Exposure History
CDC states that symptoms may appear 2 to 14 days after exposure, with a median of 3 to 4 days during Omicron circulation. Recent contact and setting form part of the assessment.
Testing, Because Symptoms Are Not Enough
CDC states plainly that you cannot tell the difference between influenza and COVID-19 by symptoms alone, because many of the signs are the same, so testing is needed to confirm a diagnosis.
Measuring Oxygen Levels
CDC grades severity by oxygen saturation. Mild to moderate illness sits at 94% or above on room air, and severe illness below 94% or needing supplemental oxygen.
Chest Imaging
Chest imaging is used in hospital assessment, and CDC notes abnormalities may appear before symptoms begin.
Assessment for Long COVID
CDC defines Long COVID as a chronic condition that occurs after infection and is present for at least 3 months.
Laboratory Tests
Nucleic Acid Amplification Test, including PCR
Described by CDC as the most reliable test. A positive result means the virus was detected and you have or recently had an infection.
Rapid Antigen Test, including self-tests
Detects viral proteins. Less sensitive than a PCR test, so a negative result may need repeating, but CDC states positive results are accurate and reliable.
Combined Test for COVID-19 and Influenza
CDC states a combined test is ideal where both viruses circulate, because it guides antiviral treatment decisions for either illness.
Antibody Test
Shows past infection or vaccination. CDC states clearly that antibody testing does not diagnose current infection and is not recommended for checking protection.
Treatment
Nirmatrelvir with Ritonavir
An antiviral taken at home that stops the virus multiplying. CDC states it must begin within 5 days of when symptoms start and that it interacts with other medicines more often than the alternatives, so tell the prescriber everything you take.
Remdesivir
Given at a health facility. CDC states it must begin within 7 days of when symptoms start.
Molnupiravir
An alternative oral antiviral for adults where the other options are unsuitable.
Supportive Care at Home
Rest, fluids and simple medicines such as paracetamol for fever and aches. WHO states most people recover from mild illness without needing specific treatment.
Hospital Oxygen and Ventilation Support
Severe illness is treated with supplemental oxygen and, where needed, high-flow oxygen or ventilation.
Prevention
Stay up to date with vaccination
WHO states that vaccination remains protective against severe disease and recommends revaccination after 6 to 12 months for people at high risk.
Stay home when you are unwell
WHO lists this first among its prevention measures, because it stops the illness reaching other households.
Wear a well-fitting mask when symptomatic or around vulnerable people
A properly fitted mask reduces the respiratory particles you release and breathe in.
Clean your hands frequently
WHO advises cleaning hands frequently with soap and water or an alcohol-based rub.
Improve indoor ventilation
Opening windows and improving airflow lowers the concentration of virus in shared indoor air.
Cover coughs and sneezes
WHO advises covering the mouth and nose with a bent elbow or a tissue.
Risk Factors
Older Adults
CDC identifies age as the strongest single risk factor for severe COVID-19.
- Adults over 65 years, where CDC reports more than 81% of COVID-19 deaths occur
- Risk increases substantially above 75 years
- CDC reports deaths in people over 65 at 97 times the rate of people aged 18 to 29
- Older adults living in shared residential settings
People with Chronic Conditions
CDC lists a wide range of long-term conditions that raise the risk of severe illness.
- Diabetes, heart disease, stroke and chronic kidney disease
- Chronic lung disease including asthma, bronchiectasis and COPD
- Cancer, chronic liver disease and sickle cell disease
- Obesity, physical inactivity and current or former smoking
People with Weakened Immunity
A weakened immune system reduces the response to both infection and vaccination.
- People living with HIV, particularly when it is untreated
- Organ or stem cell transplant recipients
- People taking medicines that suppress the immune system
- People with tuberculosis
Pregnancy and Unvaccinated People
Both WHO and CDC name these groups among those facing elevated risk.
- Pregnant women, whom WHO lists among high-risk groups
- Unvaccinated people of any age
- Children with medical complexity or chronic conditions
- People with disabilities, whom CDC names among the main risk categories
Complications
Respiratory Failure
CDC lists low blood oxygen and acute respiratory distress syndrome among the complications of severe COVID-19.
Sepsis and Septic Shock
A body-wide response to infection that can cause organ failure.
Blood Clots
CDC lists clots in the veins and lungs among the complications of severe disease.
Secondary Infections
CDC lists hospital-acquired pneumonia and other bacterial and fungal infections acquired during a hospital stay.
Damage to Other Organs
CDC lists heart, blood vessel, hormonal, liver, kidney, digestive and nervous system illness among the complications of severe disease.
Long COVID
WHO states that about 6% of people develop post COVID-19 condition, with symptoms such as memory problems, fatigue and breathing difficulty.
When to Seek Medical Care
Any Emergency Warning Sign
Trouble breathing, chest pain or pressure, new confusion, inability to stay awake, or pale, grey or blue skin, lips or nail beds mean calling emergency services now.
Early, If You Are at Higher Risk
Antiviral treatment must start within 5 days of symptoms for the oral medicines and within 7 days for the intravenous one, so an early call matters.
To Confirm What You Have
Symptoms overlap with influenza and other respiratory infections, and the treatment differs, so testing guides care.
If Symptoms Worsen Instead of Settling
Illness that is getting worse after the first few days needs review, particularly if breathing is affected.
If Symptoms Last Three Months or More
CDC defines Long COVID as symptoms present for at least 3 months after infection, and it can be assessed and managed.
Prognosis
Most People Recover Fully
WHO states that most people make a full recovery without needing treatment.
Recovery Usually Takes One to Two Weeks
WHO states symptoms typically emerge 3 to 6 days after exposure and can persist up to 10 days, with fatigue often lasting longer.
Risk Is Concentrated in Older Adults
CDC reports that more than 81% of COVID-19 deaths occur in people over 65.
Long COVID Usually Improves
CDC states that most people with Long COVID see significant improvement after 3 months, and that vaccination is the best available tool to prevent it.
Differential Diagnosis
Influenza
CDC states the two cannot be told apart by symptoms alone and that testing is needed. Loss of taste or smell is more frequent with COVID-19.
Respiratory Syncytial Virus
RSV causes a similar illness, particularly in young children and older adults, and is separated by a specific viral test.
Common Cold
A cold rarely causes high fever or breathlessness, but early COVID-19 can be indistinguishable, so testing decides.
Malaria
In endemic areas fever must be tested for malaria, which needs entirely different treatment and can be rapidly fatal if missed.
Bacterial Pneumonia
Pneumonia can follow or mimic COVID-19 and is separated by chest imaging and the pattern of illness.
References
World Health Organization: Coronavirus disease (COVID-19)
WHO fact sheet on transmission, symptoms, prevention, treatment and post COVID-19 condition.
CDC: Symptoms of COVID-19
Symptom list and the emergency warning signs that require immediate care.
CDC: Types of COVID-19 Treatment
Antiviral options, how they are given and the time limits for starting them.
CDC: Long COVID Basics
Definition, symptoms and course of Long COVID.
Frequently Asked Questions
How long after being exposed will symptoms start?
CDC states symptoms may appear 2 to 14 days after exposure, with a median of 3 to 4 days for the variants circulating since Omicron. WHO states symptoms typically emerge 3 to 6 days after exposure and can persist up to 10 days.
Is there a tablet for COVID-19, and when must it start?
Yes. CDC lists nirmatrelvir with ritonavir and molnupiravir, both taken by mouth at home, which must begin within 5 days of when symptoms start. Remdesivir is given as an infusion at a health facility over 3 days and must begin within 7 days.
When should someone with COVID-19 go to hospital?
CDC advises calling emergency services immediately for trouble breathing, persistent chest pain or pressure, new confusion, inability to wake or stay awake, or pale, grey or blue skin, lips or nail beds. WHO adds being unable to speak in full sentences.
Do I still need a COVID-19 vaccine?
WHO recommends a single dose for people who have never been vaccinated and revaccination after 6 to 12 months for high-risk groups, including older adults, pregnant women and people who are immunocompromised. Recommendations differ by country, so ask your local health service what applies to you.
What is Long COVID and how likely is it?
CDC defines Long COVID as a chronic condition that occurs after infection and is present for at least 3 months. WHO states that about 6% of people develop it. CDC states most people improve significantly after 3 months and that vaccination is the best available tool to prevent it.