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  • Facts about the virus and COVID-19 disease

Facts about the SARS-CoV-2 virus and COVID-19 disease

Published Updated

The SARS-CoV-2 coronavirus was discovered in January 2020. New knowledge about the outbreak, the disease and risks will be regularly updated.

Foto: CDC, Alissa Eckert
Foto: CDC, Alissa Eckert

The SARS-CoV-2 coronavirus was discovered in January 2020. New knowledge about the outbreak, the disease and risks will be regularly updated.

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About the virus

The coronavirus family includes many different viruses that can cause respiratory infection. Many coronaviruses only cause colds, while others can cause more serious illness and in some cases, death.

The novel coronavirus SARS-CoV-2 was first discovered in January 2020. It has some genetic similarities to the SARS virus (Severe Acute Respiratory Syndrome) which also belongs to the coronavirus family. The virus that causes MERS (Middle East Respiratory Syndrome) is another coronavirus. 

Coronaviruses are also detected in animals. In rare cases, these coronaviruses can develop so they can transmit from animals to humans and between humans, as seen during the SARS epidemic in 2002. The infection probably came from bats via civet cats and other animals.  and , where dromedary camels were the source of infection for the MERS virus discovered in 2012.

SARS-CoV-2 is believed to come from bats and was transmitted to humans in the end of 2019, either directly or via other animals. 

Different variants of SARS-CoV-2

As with other viruses, there are small changes in the genetic material (RNA) of SARS-CoV-2 as it multiplies. These are called mutations. The vast majority of these changes have no effect on the properties of the virus, but occasionally some, or combinations of changes, will appear that can change the properties. The new type of virus is then called a variant. Some variants can potentially have negative consequences for the further development of the pandemic.

So far, some variants of SARS-CoV-2 have been identified that are being closely monitored:

UK variant

B.1.1.7 was first discovered in England and is the variant we currently know most about. It has a number of mutations in key areas of the virus' RNA that make altered properties possible.

This variant is somewhat more contagious. This is supported by several different observations, but the exact mechanism behind the increased infectivity is still unclear.
There is no evidence that this variant can more easily infect people who have been vaccinated or have had an infection.

South African variant

B1.351 was first discovered in South Africa. This also has a number of mutations that can be potentially problematic. It shares some mutations with B.1.1.7, while others are specific to this variant.

  • It is possible that this variant might also be somewhat more contagious, but current knowledge is lacking.
  • So far, there is no evidence that it causes more severe disease.
  • It is possible that this variant can infect people who have previously undergone the infection or have been vaccinated to some extent, but current knowledge is lacking.

Brazilian variant

B.1.1.248 / P.1, from Brazil has similar mutations to the South African B1.351. Less is known about the properties of this variant, but preliminary data indicate that it is similar to B1.351.


Infection with the SARS-CoV-2 virus occurs mainly following close contact (less than 1 metre) by exposure to droplets that contain viruses from the respiratory tract. COVID-19 patients are most contagious in the days around the onset of symptoms. Someone can be infected with SARS-CoV-2 virus without developing COVID-19 disease, but can still transmit the virus further (asymptomatic carriers). The significance of asymptomatic transmission is still very uncertain, but probably lower than from people who have symptoms.

The coronavirus can be transmitted from the patient's respiratory tract in three main ways:

  • Droplet transmission: People with COVID-19 disease emit droplets and particles from their nose and mouth that contain SARS-CoV-2. The droplets / particles come in different sizes and amounts depending on the situation. The amount increases with, for example, exercising, singing and coughing / sneezing. Infection can occur when virus-containing droplets and particles come in contact with the mucosa of the eyes, nose or mouth, or if they are breathed into the respiratory tract. The significance of the various droplet sizes for transmission is still uncertain. When transmission occurs within 1-2 metres of someone who is contagious, it is called droplet transmission. Studies indicate that the risk of infection decreases rapidly with increasing distance to the contagious person, and that the risk of infection is reduced by 80 per cent if you keep a distance of one metre.

  • Direct contact: Droplets / particles containing the virus from the respiratory tract land on nearby surfaces and are transmitted from there to the respiratory tract of another person. Contact transmission occurs either through direct contact with a contagious person (for example, by a hug or handshake) or indirectly via contact with other surfaces contaminated with viruses (door handles, light switches, handrails, etc.)
    Research indicates that coronaviruses (including current information about the new virus) can survive on surfaces from a few hours to several days. This depends upon amount of virus, type of surface, temperature, sunlight and air humidity. Experimental studies show that just because a virus can survive on different surfaces does not mean it will cause infection in humans.

  • Airborne transmission: Tiny virus-containing droplets / particles from the nose and mouth of an infectious person can remain suspended in the air for a long time and move over longer distances. The amount of droplets / particles and virus decreases rapidly over time and with increasing distance. To become infected, someone must be exposed to a certain amount of infectious virus. For SARS-CoV-2, this amount is unknown, but modelling studies indicate that the amount of infectious virus to which they are exposed at distances of more than 1-2 metres will seldom be sufficient to cause infection. In some situations, however, it is possible that airborne transmission can occur, and cases have been reported where this may have been the mode of transmission. This happened in small rooms with poor ventilation (Inneklima og risiko for smitte av covid-19 - Råd om ventilasjon). However, airborne transmission is considered to be significant in some medical procedures performed in the healthcare service, so-called aerosol-generating procedures. In these situations, NIPH recommends that healthcare professionals use extra protective equipment.

Which situations involve a greater risk of transmission?

It is not documented how many COVID-19 patients are infected by each mode of transmission, but droplet transmission is assumed to be the most important one.

Individual differences in how much virus and droplets a person produces have been documented. Some people can produce up to 10-100 times more droplets than others. Several studies indicate that 10–30 per cent of those infected can account for about 80 per cent of the infection, and they are often referred to as super-spreaders. Super-spreading cases can occur in situations where many have been with one or more contagious people for a long time, often indoors in rooms with limited space. Limited air volume and air circulation increases the concentration of virus-containing droplets / particles, in addition to poor ventilation with infrequent air exchange in the room. In addition, the contagious person was often been at the beginning of their disease phase, the highest amount of virus is usually present in the days around the onset of symptoms.

The virus has been detected in faeces (stools), blood and urine, but it has none been shown that anyone has been infected by contact with these bodily fluids.

Infection from food, water and animals

Currently, there are no known cases of infection via food produced in Norway or imported, or from water and animals. Several systematic reviews have concluded that this is an unlikely mode of transmission.

There have been some cases of transmission between animals and humans. Mink and other species in the marten family appear to be highly susceptible to infection, and both human-to-mink and mink-to-human infections have occurred in the Netherlands and Denmark. It is important that people with COVID-19 or people in quarantine do not go to work as keepers and have close contact with mink.

Infection from animals does not appear to play a role in transmission of the virus.

In the case of swimming pools, the chlorine content of the pool water will be sufficient to inactivate coronaviruses and other viruses. However, physical contact in changing rooms and by the pool could lead to transmission as with any other close contact. 

How contagious is it?

Calculations estimate that a person infected with coronavirus infects 2-3 others whereas a person with influenza will infect 1-2 people. Probably fewer than 20 per cent of those infected with SARS-CoV-2 virus account for 80 per cent of the transmission. This indicates that the majority of confirmed cases will not transmit further, while a minority will infect many.

The number will probably be lower than 2-3 in Norway because we have a lower population density and have implemented infection control measures. 


The incubation time (from infection until symptoms appear) is usually 5-6 days. Based on current figures, 98 - 99.9% of infected people develop symptoms within 10 days.

Symptoms and disease

The new coronavirus causes respiratory infections, ranging from mild symptoms to severe disease and, in rare cases, death.

Some people may have COVID-19 without developing symptoms. This is especially true for children and younger adults. 

Usually, people who become ill first develop upper respiratory tract symptoms (sore throat, cold symptoms, mild cough), as well as feeling generally unwell and having muscle pain. Stomach pains may be present and diarrhoea may occur in some cases. Loss of the senses of smell and taste is also reported.

The course of the disease varies widely between individuals. Currently, the typical courses appear to be:

  • Mild course: This applies to the majority of people who become sick. Symptoms pass within one to two weeks. These people rarely need treatment from the healthcare service.
  • Moderate course: After 4-7 days of mild symptoms, some people may develop pneumonia with breathing difficulties, worsening cough and rising fever. Some will need to be admitted to hospital. X-ray examination of the lungs may show changes consistent with viral pneumonia (pulmonary infiltrates)
  • Severe course: As for the moderate course, but these people also need intensive care treatment. They may have symptoms for 3-6 weeks. As for other serious infections, different complications can arise with severe COVID-19, including lung damage, cardiovascular disease and coagulation disturbances (5-8). Some people who become seriously ill may die. 

Admission to hospital, intensive care treatment and death are more common among the elderly and people with underlying diseases, particularly among the elderly with underlying diseases, but can also occur among people without known risk factors.

There is no specific treatment or vaccine for the disease, but vaccines are under development.

More about the symptoms of COVID-19

It appears that SARS-CoV-2 mainly infects upper and lower respiratory tract cells and causes respiratory tract infection with symptoms such as cough, fever and sore throat. Most people who get COVID-19 only develop these symptoms.

A minority enter a more severe phase with breathing difficulties and symptoms of systemic disease that are probably caused by the body's immune response to the infection. There is a good basis to assume that SARS-CoV-2 also infects the gastrointestinal tract, and related symptoms are frequently reported.

We are learning more about the symptoms of COVID-19. Much of the knowledge is based on patients admitted with severe disease. These account for about 20 per cent of all people who develop symptoms and probably do not reflect the overall clinical presentation.

Among the vast majority with a mild disease course, these are probably the most common symptoms: respiratory tract symptoms (cough, runny nose and sore throat), headache, and mildly reduced general condition (lethargy, mild muscle aches). Fever is often seen in hospitalised patients (over 80%), but it otherwise seems to affect less than 20% of all COVID-19 patients.

Altered taste and sense of smell appear to be a fairly specific symptom of COVID-19. Nevertheless, the occurrence of this is far from certain. Studies have reported this in 5 to 98% of cases. The real figure is probably around 30 to 50 %.

Shortness of breath (dyspnoea) is frequently reported (15-40 %) and is an indication of severe disease that often requires hospitalisation. The proportion that develops shortness of breath appears to be small if mild cases are included in the calculation.

Gastrointestinal symptoms such as pain, nausea / vomiting and diarrhoea have been reported in 2-40 % of cases. In one meta-study of 4243 patients, 17.6 % of patients had gastrointestinal symptoms, which may be the first and, in some cases, the only obvious symptom of the disease.

Neurological symptoms other than headache and changes in senses of taste and smell. These may include dizziness, altered mental state, ataxia and tremor. Cases of diarrhoea and haemorrhagic strokes, encephalopathy and Guillain-Barré are also linked to SARS-CoV-2 infection.

In addition, symptoms have been reported for most organ systems such as the eye (e.g., conjunctivitis), skin (rash), heart (myocarditis, arrhythmias, infarction) and kidneys (acute kidney damage) associated with the disease.

Coagulation disorders

Coagulation disorders appear to occur frequently in seriously ill COVID-19 patients, but are also described among patients with mild disease. This may explain symptoms such as blood clots in the lungs (pulmonary embolism) and deep vein thrombosis, and also some of the neurological and cardiovascular symptoms described above. 

Silent hypoxia

There is an increase in the number of reports of COVID-19 patients with hypoxia without dyspnoea or other symptoms of hypoxia. The clinical significance of this is currently unknown, but frequent measurement with an oximeter may be considered in COVID-19 patients at risk of a severe course (for example, in a hospital). Patients with silent hypoxemia should be assessed by a doctor for possible causes, such as pulmonary embolism.

Symptoms of COVID-19 among the elderly

High age is the most certain risk factor for severe disease and death from COVID-19.

Elderly patients often have an atypical clinical presentation with many diseases and this also applies to COVID-19. In addition to the symptoms mentioned above, there are a number of atypical symptoms that occur among the elderly with COVID-19, such as delirium (acute onset of cognitive failure and altering emotions and behaviour), confusion (new-onset or deterioration), tendency to fall (new-onset or deterioration), lethargy and weakness (new-onset or deterioration), generally poorer function level, weight loss, decreased appetite. Elderly people with dementia have a significantly increased risk of delirium with infections. These symptoms may overshadow other and more common symptoms of infection, such as respiratory problems.

The reason why older people more often present with atypical symptoms may be age-related changes in the immune system, temperature regulation may be poorer, and the ability to remember and recall symptoms may be impaired. Elderly people also more often have underlying chronic conditions that can affect the clinical presentation, e.g., strokes and other neurological disorders can impair the cough reflex.

Therefore, COVID-19 should be considered as a differential diagnosis among the elderly, even with atypical and / or mild symptoms.

Symptoms that are particularly important to be alert for in this group are tachypnea (rapid breathing), tachycardia (rapid heartbeat), hypotension (low blood pressure) and low-grade fever (above 37.5 °C).

The assessment of elderly patients should be made by people who are familiar with the patient’s normal functional level so that changes can be detected quickly; Here, both health professionals and relatives can play a role. An early diagnosis will ensure the best possible treatment and prevent the spread of infection, especially in hospital and nursing homes.

Symptoms among children

Children appear to have a similar clinical presentation to adults, but the proportion with severe disease is much lower. Most have symptoms of colds, such as cough, fever and sore throat, which last from several days to a week.

Fever (41-48 %) and cough (39-48 %) are the two most common symptoms. A sore throat was observed among 46 % in one study. Other relatively frequently reported symptoms are diarrhoea (7-9 %), nausea / vomiting (6 %), lethargy (7.6 %), mucus and runny nose (7.6 %). Other rarer symptoms include stuffy nose, headache, abdominal pain and shortness of breath.

Multisystemic Inflammatory Disease in Children (MIS-C)

At the end of April 2020, British health authorities reported that an increasing number of children were admitted to intensive care with symptoms similar to Kawasaki disease. 4 out of 8 children had previously known exposure to SARS-CoV-2.

The condition has now been reported worldwide and is called MIS-C. The condition is similar, and sometimes overlaps with Kawasaki syndrome, which is an acute condition with inflammation of blood vessels in various parts of the body. Typical of Kawasaki is fever for more than 5 days, rash, mucous membrane changes on the lips and in the oral cavity, inflammation of the eye without pus, swollen lymph nodes on the neck and swollen / red hands and feet.

In contrast to Kawasaki syndrome, which is most commonly seen in children under 5 years of age, MIS-C usually affects older children and adolescents.

Typical for MIS-C are fever, abdominal pain, diarrhoea and various types of organ failure (heart, kidney, liver). The condition follows 2-6 weeks after undergoing SARS-CoV-2 infection, and is the cause of a severe inflammatory picture and coagulation disorders. Treatment is similar to that for Kawasaki syndrome, with immunomodulatory drug (intravenous immunoglobulin, steroids). The prognosis is usually very good.

It has not been possible to define which children are exposed to developing MIS-C, but the condition is still very rare.

ECDC and WHO stress that COVID-19 mainly causes mild illness among children, and that it is extremely rare for children to become seriously ill. The most important advice for parents is the same as always: they should seek medical attention when a child with a fever has a poor general condition and they are concerned for their child, for whatever reason.

Information about om MIS-C:

ECDC and WHO's assessments can be found here:

Long-term health consequences of COVID-19

COVID-19 is a new disease, and little is yet known about long-term health consequences (sequelae) after having had COVID-19. Several studies about this have been initiated both in Norway and abroad.

For most people, COVID-19 is a mild and short-lived disease. However, it has also been reported that people who had a mild course of the disease may struggle with long-term symptoms. 

The most commonly reported include fatigue, headaches, difficulty breathing, anxiety and depression, chest pains, joint pains and dizziness. For the majority, these symptoms will improve with time, but the frequency and duration of these symptoms are still unknown.

It is already known that people who are treated for severe respiratory failure in intensive care units due to other diseases may struggle with long-term disability after discharge from hospital, such as impaired cognitive function and impaired lung function. Since respiratory failure and long-term intensive care treatment occur during severe COVID-19 disease courses, similar sequelae could be expected.


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12.02.2020 Updated according to Norwegian version

11.12.2020 updated information about incubation time

23.11.2020 general updates as per Norwegian version

20.11.2020 Added paragraph about long-term health consequences

17.07.2020 Changed value from 10 to 5 in "Aerosols smaller than 5 µm can remain suspended in the air for a long time" under "More about transmission"

14.07.2020 Updated text in section about Transmission route

07.07.2020 Removed sentence about coronavirus transmission being traced back to direct or indirect physical contact, as well as the number of summaries and studies.

06.07.2020 Added paragraph about mink.

01.07.2020 Added paragraph about wastewater surveillance.

19.06.2020 Updated text as per Norwegian version. Added references and factbox about symptoms.

27.04.2020  Updated sentence about closure of swimming baths etc. 

Added symptoms, stomach ache, loss of senses of smell and taste.

Added paragraph about water. Changed title. Removed paragraph about how infection is handled in Norway to article about Infection Control Measures. Added paragraph about airborne transmission with link to systematic review fra FHI. Added symptoms.

Moved section about infection from animals to this article to reflect the Norwegian version


Changes according to Norwegian text. WHO declares a pandemic. Update about risk assessment

Changes according to Norwegian text. Added information about virus properties on surfaces.


Changes according to Norwegian text. Moved section about pregnancy to "advice to public" article. Updated "what is NIPH role?" and "About the outbreak"

Changes according to updates in the Norwegian text - advice to pregnant women and risk groups

Paragraph about risk assessment added and what happens in Norway updated according to the Norwegian version

Paragraph about affected countries removed and published as its own page.

Changed name of virus from COVID-19 to SARS-CoV-2

Removed sentence about which countries are in mainland China.

Changed the name of the virus from "2019-nCoV" to "COVID-19".