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
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
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
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
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
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.
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
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:
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)
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
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.
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
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
shortness of breath
nausea or vomiting
How long does the virus last on clothes and surfaces?
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:
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
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.
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
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
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
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
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
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.
COVID-19 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
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
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
In a meta-analysis, smokers were 1.5 times more likely to
have severe complications from COVID-19 and had a higher
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
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.
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.
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
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