The ongoing global pandemic of coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was identified in Wuhan, China, in December 2019; a lockdown in Wuhan and other cities in Hubei province failed to contain the outbreak, and it spread to other parts of mainland China and around the world. The World Health Organization (WHO) declared a Public Health Emergency of International Concern on 30 January 2020, and a pandemic on 11 March 2020. Since 2021, variants of the virus have emerged or become dominant in many countries, with the Delta, Alpha and Beta variants being the most virulent. As of 21 August 2021, more than 211 million cases and 4.42 million deaths have been confirmed, making it one of the deadliest pandemics in history.
COVID-19 symptoms range from unnoticeable
to life-threatening. Severe illness is more likely in elderly patients, as well
as those who have certain underlying medical conditions. The disease transmits when people breathe in
air contaminated by droplets and small airborne particles. The risk of breathing these in is highest when
people are in close proximity, but still present over longer distances,
particularly indoors. Transmission can also occur if splashed or sprayed with
contaminated fluids in the eyes, nose, or mouth, and, rarely, via contaminated
surfaces. People remain contagious for up to 20 days, and can spread the virus
even if they do not develop any symptoms.
Recommended preventive measures include social
distancing, wearing face masks in public, ventilation and air-filtering, hand
washing, covering one's mouth when sneezing or coughing, disinfecting surfaces,
and monitoring and self-isolation for people exposed or symptomatic. Several vaccines have been distributed in many
countries since December 2020. Treatments
focus on addressing symptoms, but work is underway to develop medications that
inhibit the virus. Authorities worldwide have responded by implementing travel
restrictions, lockdowns and quarantines, workplace hazard controls, and
business closures. There are also efforts to increase testing capacity and trace
contacts of the infected.
The pandemic has resulted in severe
global social and economic disruption, including the largest global recession since
the Great Depression of the 1930s. It
has led to widespread supply shortages exacerbated by panic buying,
agricultural disruption, food shortages, and decreased emissions of pollutants.
Numerous educational institutions and
public areas have been partially or fully closed, and many events have been
cancelled or postponed. Misinformation
has circulated through social media and mass media, and political tensions have
been exacerbated. The pandemic has raised issues of racial and geographic
discrimination, health equity, and the balance between public health
imperatives and individual rights.
Background
Although the exact origin of the virus
is still unknown, the first outbreak started in Wuhan, Hubei, China in November
2019. Many early cases of COVID-19 were linked to people who had visited the Huanan
Seafood Wholesale Market in Wuhan, but it is possible that human-to-human
transmission was already happening before this.
On 11 February 2020, the World Health Organization (WHO) named the
disease "COVID-19", which is short for coronavirus disease 2019. The virus that caused the outbreak is known
as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a newly
discovered virus closely related to bat coronaviruses, pangolin coronaviruses, and
SARS-CoV. The scientific consensus is
that the virus is most likely of zoonotic origin, from bats or another
closely-related mammal. Despite this,
the subject has generated a significant amount of speculation and conspiracy
theories, which were amplified by rapidly growing online echo chambers. Global geopolitical divisions, notably
between the United States and China, have bee0n heightened because of this
issue.
The earliest known person with symptoms
was later discovered to have fallen ill on 1 December 2019, and that person did
not have visible connections with the later wet market cluster. However, an earlier case of infection could
have occurred on 17 November. Of the
early cluster of cases reported that month, two-thirds were found to have a
link with the market. Molecular clock analysis
suggests that the index case is likely to have been infected with the virus
between mid-October and mid-November 2019.
Cases of COVID-19
Official case counts refer to the number
of people who have been tested for COVID-19 and whose test has been confirmed
positive according to official protocols.
Many countries, early on, had official policies to not test those with
only mild symptoms. An analysis of the
early phase of the outbreak up to 23 January estimated 86 per cent of COVID-19
infections had not been detected, and that these undocumented infections were
the source for 79 per cent of documented cases.
Several other studies, using a variety of methods, have estimated that
numbers of infections in many countries are likely to be considerably greater
than the reported cases.
On 9 April 2020, preliminary results found
that 15 per cent of people tested in Gangelt, the centre of a major infection
cluster in Germany, tested positive for antibodies. Screening for COVID-19 in pregnant women in
New York City, and blood donors in the Netherlands, has also found rates of
positive antibody tests that may indicate more infections than reported. Seroprevalence based estimates are conservative
as some studies show that persons with mild symptoms do not have detectable
antibodies. Some results (such as the
Gangelt study) have received substantial press coverage without first passing
through peer review.
An analysis in early 2020 of cases by
age in China indicated that a relatively low proportion of cases occurred in
individuals under 20. It was not clear
whether this was because young people were less likely to be infected, or less
likely to develop serious symptoms and seek medical attention and be tested. A retrospective cohort study in China found
that children and adults were just as likely to be infected.
Initial estimates of the basic
reproduction number (R0) for COVID-19 in January were between 1.4
and 2.5, but a subsequent analysis concluded that it may be about 5.7 (with a
95 per cent confidence interval of 3.8 to 8.9).
R0 can vary across populations and is not to be confused with
the effective reproduction number (commonly just called R), which takes into
account effects such as social distancing and herd immunity. By mid-May 2020, the effective R was close to
or below 1.0 in many countries, meaning the spread of the disease in these
areas at that time was stable or decreasing.
Deaths
Official deaths from COVID-19 generally
refer to people who died after testing positive according to protocols. These
counts may ignore deaths of people who die without having been tested. Conversely, deaths of people who had
underlying conditions may lead to over-counting. Comparisons of statistics for deaths for all
causes versus the seasonal average indicate excess mortality in many countries. This may include deaths due to strained healthcare
systems and bans on elective surgery. The
first confirmed death was in Wuhan on 9 January 2020. Nevertheless, the first reported death
outside of China occurred on 1 February 2020 in the Philippines, and the
first reported death outside Asia was in the United States on 6 February 2020.
More than 95 per cent of the people who contract COVID-19 recover.
Otherwise, the time between symptoms onset and death usually ranges from 6
to 41 days, typically about 14 days. As
of 21 August 2021, more than 4.42 million deaths have been attributed to
COVID-19. People at the greatest risk of mortality from COVID-19 tend to be
those with underlying conditions, such as those with a weakened immune system,
serious heart or lung problems, severe obesity, or the elderly (including
individuals age 65 years or older).
Multiple measures are used to quantify
mortality. These numbers vary by region
and over time, influenced by testing volume, healthcare system quality,
treatment options, government response, time since the initial outbreak, and
population characteristics, such as age, sex, and overall health. Countries like Belgium include deaths from
suspected cases of COVID-19, regardless of whether the person was tested,
resulting in higher numbers compared to countries that include only
test-confirmed cases.
The death-to-case ratio reflects the
number of deaths attributed to COVID-19 divided by the number of diagnosed
cases within a given time interval. Based on Johns Hopkins University
statistics, the global death-to-case ratio is 2.09 percent (4,420,984
deaths for 211,232,169 cases) as of 21 August 2021. The number varies by region.
Signs and Symptoms
Symptoms of COVID-19 are variable,
ranging from mild symptoms to severe illness.
Common symptoms include headache, loss of smell and taste, nasal
congestion and runny nose, cough, muscle pain, sore throat, fever, diarrhea,
and breathing difficulties. People with
the same infection may have different symptoms, and their symptoms may change
over time. Three common clusters of symptoms have been identified: one
respiratory symptom cluster with cough, sputum, shortness of breath, and fever;
a musculoskeletal symptom cluster with muscle and joint pain, headache, and
fatigue; a cluster of digestive symptoms with abdominal pain, vomiting, and diarrhea. In people without prior ear, nose, and throat
disorders, loss of taste combined with loss of smell is associated with COVID-19.
Of people who show symptoms, 81% develop
only mild to moderate symptoms (up to mild pneumonia), while 14% develop severe
symptoms (dyspnea, hypoxia, or more than 50% lung involvement on imaging) and
5% of patients suffer critical symptoms (respiratory failure, shock, or multiorgan
dysfunction). At least a third of the
people who are infected with the virus do not develop noticeable symptoms at
any point in time. These asymptomatic carriers
tend not to get tested and can spread the disease. Other infected people will develop symptoms
later, called "pre-symptomatic", or have very mild symptoms and can
also spread the virus.
As is common with infections, there is a
delay between the moment a person first becomes infected and the appearance of
the first symptoms. The median delay for COVID-19 is four to five days. Most symptomatic people experience symptoms
within two to seven days after exposure, and almost all will experience at
least one symptom within 12 days.
Most people recover from the acute phase
of the disease. However, some people – over half of a cohort of home-isolated
young patients – continue to experience a range of effects, such as fatigue,
for months after recovery, a condition called long COVID; long-term damage to
organs has been observed. Multi-year studies are underway to further
investigate the long-term effects of the disease.
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