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1. Causes of Coronavirus: Origin and how it spreads

Many health experts believe that the new strain of coronavirus likely originated in bats or pangolins. The first transmission to humans was in Wuhan, China. Since then, the virus has mostly spread through person-to-person contact.

Coronaviruses are a group of viruses that can cause disease in both animals and humans. The severe acute respiratory syndrome (SARS) virus strain known as SARS-CoV is an example of a coronavirus. SARS spread rapidly in 2002-2003.

The new strain of coronavirus is called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus causes coronavirus disease 19 (COVID-19).

Around 80%Trusted Source of people with COVID-19 recover without specialist treatment. These people may experience mild, flu-like symptoms. However, 1 in 6 peopleTrusted Source may experience severe symptoms, such as trouble breathing.

The new coronavirus has spread rapidly in many parts of the world. On March 11, 2020, the World Health Organization (WHO)Trusted Source declared COVID-19 a pandemic. A pandemic occurs when a disease that people are not immune to spreads across large regions.

What caused coronavirus?

The recent outbreak began in Wuhan, a city in the Hubei province of China. Reports of the first COVID-19 cases started in December 2019.

Coronaviruses are common in certain species of animals, such as cattle and camels. Although the transmission of coronaviruses from animals to humans is rareTrusted Source, this new strain likely came from bats, though one study suggests pangolins may be the origin.

However, it remains unclear exactly how the virus first spread to humans.

Some reports trace the earliest cases back to a seafood and animal market in Wuhan. It may have been from here that SARS-CoV-2 started to spread to humans.

How it spreads

SARS-CoV-2 spreads from person to person through close communities.

When people with COVID-19 breathe out or cough, they expel tiny droplets that contain the virus. These droplets can enter the mouth or nose of someone without the virus, causing an infection to occur.

The most common way that this illness spreads is through close contact with someone who has the infection. Close contact is within around 6 feetTrusted Source.

The disease is most contagious when a person’s symptoms are at their peak. However it is possible for someone without symptoms to spread the virus. A new study suggests that 10% of infections are from people exhibiting no symptoms.

Droplets containing the virus can also land on nearby surfaces or objects. Other people can pick up the virus by touching these surfaces or objects. Infection is likely if the person then touches their nose, eyes, or mouth.

It is important to note that COVID-19 is new, and research is still ongoing. There may also be other ways that the new coronavirus can spread.

Is it more dangerous than other viruses?

Most cases of COVID-19 are not serious. However, it can cause symptoms that become severe, leading to death in some cases.

The outbreak of COVID-19 has been sudden. This makes it difficult to estimate how often the disease becomes severe or the exact rate of mortality.

One report suggests that out of 1,099 people with confirmed cases in China, around 16% became severe. Another report estimates that about 3.6%Trusted Source of the confirmed cases in China led to death.

These figures are likely to change as the situation evolves. However, they suggest that COVID-19 is more deadly than influenza. For example, seasonal influenza typically leads to death in less than 0.1%Trusted Source of cases.

When testing becomes easier and more widespread, health experts will have a more accurate insight into the exact number of severe cases and deaths.

SARS is another type of coronavirus. It became a global pandemic in 2002-2003. Around 9.6%Trusted Source of SARS cases led to death. However, COVID-19 is more contagious, and it is already the cause of more deaths worldwide.

2. How long does coronavirus last in the body?

The novel coronavirus, SARS-CoV-2, is the virus responsible for causing the illness COVID-19. Most people who develop COVID-19 symptoms improve without treatment in 2-6 weeks. However, this does not necessarily reflect how long the virus itself remains active in the body.

COVID-19 has an incubation period, meaning it can be days before a person notices symptoms. In the case of SARS-CoV-2, a person can transmit the virus 48 hours before developing symptoms.

Many people experience mild symptoms, while some experience no symptoms at all. This can make it difficult to tell who has the virus.

How long the virus lasts in the body depends on the individual and the severity of the illness. The Centers for Disease Control and Prevention (CDC) advise that people who test positive for COVID-19 should isolate themselves for the following amount of time:


Severity Transmission period
No symptoms 10 days after a positive test
Mild or moderate illness 10 days after symptoms appear, and after 24 hours with no fever (without using medications)
Severe illness Up to 20 days after symptoms appear


These figures represent when a person is most at risk for transmitting SARS-CoV-2 to others.

However, the virus may remain in the body at low levels for up to 3 months after diagnosis. This may mean some people get a second positive test result even after they recover, although this does not necessarily indicate the virus is still transmissible.

How long do symptoms last?

Early in the COVID-19 pandemic, health organizations advised that, for most people, symptoms would last a short amount of time. However, since then, people have reported that their symptoms last much longer than this.

A July 2020 CDC report found that 35% of people who had mild cases of COVID-19 were not back to their usual state of health 14-21 days after testing positive. Among those aged 18-34 years with no chronic medical conditions, one in five had not returned to their usual state of health.

This suggests that, for some people, COVID-19 symptoms last longer than original estimates, even in mild cases. By comparison, over 90% of people with influenza, or flu, recover within approximately 2 weeks of having a positive test result.

People who require hospital treatment or who experience “long COVID” may also have longer-lasting symptoms. Long COVID, or post-COVID syndrome, is a name for a collection of symptoms that some people continue to experience months after their initial illness.

The symptoms of post-COVID syndrome can include, but are not limited to:

  • severe fatigue

  • trouble sleeping

  • shortness of breath

  • headaches

  • muscle weakness

  • heart palpitations

  • low-grade fever

  • trouble concentrating

  • memory lapses

  • mood changes

  • skin rashes

  • nausea or vomiting

  • diarrhea

How long does the virus last on clothes and surfaces?

A study from the New England Journal of Medicine investigated how long SARS-CoV-2 would survive on various surfaces, including plastic, stainless steel, copper, and cardboard. The findings suggest that the virus could survive for:

  • 4 hours on copper

  • 24 hours on cardboard

  • 72 hours on plastic and steel

However, while researchers can detect SARS-CoV-2 on various surfaces under laboratory conditions, it is unclear if this corresponds to a risk of infection under normal circumstances.

A September 2020 study in The Lancet found that when researchers swabbed various surfaces in a major hospital in Italy, only one item of protective equipment tested positive for SARS-CoV-2. They conclude that, as long as people follow standard cleaning procedures, the risk of transmission from surfaces is low.

How long does it last in the air?

The study on surfaces also found that SARS-CoV-2 could survive in aerosol form for 3 hours. An aerosol is a fine mist of liquid suspended in a gas, such as air.

As the experiment ended after 3 hours, the total amount of time that SARS-CoV-2 survives in the air could be longer. However, some factors, such as air temperature and humidity, may also play an important role.

A June 2020  review notes that other coronaviruses survive for longer in colder, less humid air. This may mean SARS-CoV-2 will become a more seasonal virus in some climates. The study on surfaces also did not consider how the virus might travel through the air in everyday situations.

SARS-CoV-2 spreads via respiratory droplets, which are tiny drops of liquid that enter the air when a person coughs, sneezes, or talks. A May 2020 study found that loudly talking can emit thousands of these droplets into the air, remaining airborne for around 8-14 minutes in a confined space.

As speech droplets do not appear to remain airborne for very long indoors, a person’s proximity to someone with SARS-CoV-2 is an important risk factor for developing COVID-19.

How long does it last in food?

Currently, there is no direct evidence a person can contract SARS-CoV-2 from food. The World Health Organization (WHO) state that coronaviruses need a live animal or human host to survive, and that they cannot multiply on food packaging surfaces.

The WHO suggest washing fruits and vegetables as normal and washing hands thoroughly before eating. People should also ensure they do not share cutlery or plates with those who may have COVID-19.


The novel coronavirus, or SARS-CoV-2, is active in the body for at least 10 days  after a person develops symptoms. In people with severe illness, it may last up to 20 days. In some people, low levels of the virus are detectable in the body for up to 3 months, but by this time, a person cannot transmit it to others.

There is currently no evidence the virus can survive in food, but early evidence suggests it may last several hours on copper, 24 hours on cardboard, and up to 72 hours on plastic and steel. However, this does not necessarily mean the virus detected on these materials can trigger an infection.

Scientists are still studying how long SARS-CoV-2 can last on surfaces and clothes, and how it can travel through the air. Following guidelines for cleaning, hand washing, and masks can help keep the risk of transmission low.

3. COVID-19 risk factors

Risk factors

Some factors can affect the risk of coming into contact with the virus, while other factors can affect the risk of developing severe illness.

The risk of coming into contact with the virus depends on how far it has spread in a person’s local area.

The WHOTrusted Source state that the risk of developing COVID-19 is still low for most people. However, this is changing as the virus spreads — particularly in Europe and the United States.

The risk is higher for anyone in close contact with people who have COVID-19, such as healthcare workers. Viruses can also spread more in certain areas, such as highly populated cities.

Older adults are most at risk of severe illness, as are people with the following chronic health conditions:

  • serious heart conditions, such as heart failure, coronary artery disease, or cardiomyopathies

  • kidney disease

  • chronic obstructive pulmonary disease (COPD)

  • obesity, which occurs in people with a body mass index (BMI) of 30 or higher

  • sickle cell disease

  • a weakened immune system from a solid organ transplant

  • type 2 diabetes


Obesity increases the risk for becoming severely ill from COVID-19. In a study in France, the odds of developing severe COVID-19 were seven times higher in patients with obesity. Promoting healthy diets to maintain nutritional well-being is more important than ever in the fight against COVID-19.


In a meta-analysis, smokers were 1.5 times more likely to have severe complications from COVID-19 and had a higher mortality rate.


Alcohol impairs the body’s ability to fight infections such as COVID-19. Even a single heavy drinking session can measurably reduce immune function. Intoxication can also interfere with taking precautions against infection.


Physical activity provides multiple short- and long-term health benefits, including improving the immune system, stress and anxiety. Physical activity is also associated with prevention of heart disease, hypertension, diabetes and overweight and obesity, which are risk factors for severe COVID-19 disease.


A relation between exposure to air pollution and mortality from COVID-19 has been hypothesized. Air pollution compromises lung function, which increases the risk for vulnerability to respiratory infection, including COVID-19.


A systematic review indicated that people with diabetes were up to three times more likely to have severe symptoms or die from COVID-19, and the situation is likely to be worse for people with uncontrolled diabetes.


A meta-analysis showed that hypertension, cardiovascular and cerebrovascular disease increased the odds for severe COVID-19 by 2.3, 2.9 and 3.9 times, respectively. Another meta-analysis indicated that hypertension increased the risk of mortality from COVID-19 by 3.5 times.


In a meta-analysis, patients with chronic obstructive pulmonary disease (COPD) were at increased risk of severe complications or death from COVID-19. A study in the United Kingdom suggested that the presence of respiratory disease, including asthma, increased patients’ risk of mortality from COVID-19.


Cancer patients are more likely to experience severe COVID-19. A study in Wuhan, China, showed that the mortality rate from COVID-19 was significantly increased in patients with cancer and was particularly high among those with blood cancers.




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