COVID-19 pandemic

The COVID-19 pandemic, also known as the coronavirus pandemic, is a global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identified in an outbreak in the Chinese city of Wuhan in December 2019. Attempts to contain it there failed, allowing the virus to spread to other areas of Asia and then worldwide in early 2020. The World Health Organization (WHO) declared the outbreak a public health emergency of international concern (PHEIC) on 30 January 2020. The WHO ended its PHEIC declaration on 5 May 2023. As of 26 December 2023, the pandemic has caused 772,837,981 cases and 6,988,666 confirmed deaths, ranking it fifth in the list of the deadliest epidemics and pandemics in history.
include fever, sore throat, nocturnal cough, and fatigue. Transmission of the virus is often through airborne particles. Mutations have produced many strains (variants) with varying degrees of infectivity and virulence.
COVID-19 vaccines were widely deployed in various countries beginning in December 2020. Treatments include novel antiviral drugs and symptom control. Common mitigation measures during the public health emergency included travel restrictions, lockdowns, business restrictions and closures, workplace hazard controls, mask mandates, quarantines, testing systems, and contact tracing of the infected.
The pandemic caused severe social and economic disruption around the world, including the largest global recession since the Great Depression. Widespread supply shortages, including food shortages, were caused by supply chain disruptionsand panic buying. Reduced human activity led to an unprecedented temporary decrease in pollution. Educational institutions and public areas were partially or fully closed in many jurisdictions, and many events were cancelled or postponed during 2020 and 2021. Many white-collar workers began working from home. Misinformation circulated through social media and mass media, and political tensions intensified. The pandemic raised issues of racial and geographic discrimination, health equity, and the balance between public health imperatives and individual rights.
== Terminology ==
Further information: COVID-19 naming
epidemic occurring over a very wide area, crossing international boundaries, and usually affecting a large number of people". During the COVID-19 pandemic, as with other pandemics, the meaning of this term has been challenged.
During the initial outbreak in Wuhan, the virus and disease were commonly referred to as "coronavirus", "Wuhan coronavirus", "the coronavirus outbreak" and the "Wuhan coronavirus outbreak", with the disease sometimes called "Wuhan pneumonia". In January 2020, the WHO recommended 2019-nCoV and 2019-nCoV acute respiratory disease as interim names for the virus and disease per 2015 international guidelines against using geographical locations (e.g. Wuhan, China), animal species, or groups of people in disease and virus names in part to prevent social stigma. WHO finalized the official names COVID-19 and SARS-CoV-2 on 11 February 2020. Tedros Adhanom Ghebreyesus explained: CO for corona, VI for virus, D for disease and 19 for when the outbreak was first 
identified (31 December 2019). WHO additionally uses "the COVID-19 virus" and "the virus responsible for COVID-19" in public communications.
WHO named variants of concern and variants of interest using Greek letters. The initial practice of naming them according to where the variants were identified (e.g. Delta began as the "Indian variant") is no longer common. A more systematic naming scheme reflects the variant's PANGO lineage (e.g., Omicron's lineage is B.1.1.529) and is used for other variants.
SARS-CoV-2 is a virus closely related to bat coronaviruses, pangolin coronaviruses, and SARS-CoV. The first known outbreak (the 2019–2020 COVID-19 outbreak in mainland China) started in Wuhan, Hubei, China, in December 2019. Many early cases were linked to people who had visited the Huanan Seafood Wholesale Market there, but it is possible that human-to-human 
=== Cases ===
Main articles: COVID-19 pandemic by country and territory and COVID-19 pandemic cases
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 whether or not they experienced symptomatic disease. Due to the effect of sampling bias, studies which obtain a more accurate number by extrapolating from a random sample have consistently found that total infections considerably exceed the reported case counts. Many countries, early on, had official policies to not test those with only mild symptoms. The strongest risk factors for severe illness are obesity, complications of diabetes, anxiety disorders, and the total number of conditions.
During the start of the COVID-19 pandemic it was not clear whether young people were less likely to be infected, or less likely to develop symptoms and be tested. A retrospective cohort study in China found that children and adults were just as likely to be infected.
Among more thorough studies, preliminary results from 9 April 2020, found that in Gangelt, the centre of a major infection cluster in Germany, 15 percent of a population sample tested positive for antibodies. Screening for COVID-19 in pregnant women in New York City, and blood donors in the Netherlands, found rates of positive antibody tests that indicated more infections than reported. Seroprevalence-based estimates are conservative as some studies show that persons with mild symptoms do not have detectable antibodies.
Initial estimates of the basic reproduction number (R0) for COVID-19 in January 2020 were between 1.4 and 2.5, but a subsequent analysis claimed that it may be about 5.7 (with a 95 percent confidence interval of 3.8 to 8.9).
In December 2021, the number of cases continued to climb due to several factors, including new COVID-19 variants. As of that 28 December, 282,790,822 individuals worldwide had been confirmed as infected. As of 14 April 2022, over 500 million cases were confirmed globally. Most cases are unconfirmed, with the Institute for Health Metrics and Evaluation estimating the true number of cases as of early 2022 to be in the billions.
As of 10 March 2023, more than 6.88 million deaths had been attributed to COVID-19. The first confirmed death was in Wuhan on 9 January 2020. 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.
Multiple measures are used to quantify mortality. Official death counts typically include people who died after testing positive. Such counts exclude deaths without a test.Conversely, deaths of people who died from underlying conditions following a positive test may be included.Countries such as Belgium include deaths from suspected cases, including those without a test, thereby increasing counts.
Official death counts have been claimed to underreport the actual death toll, because excess mortality (the number of deaths in a period compared to a long-term average) data show an increase in deaths that is not explained by COVID-19 deaths alone. Using such data, estimates of the true number of deaths from COVID-19 worldwide have included a range from 18.2 to 33.5 million (≈27.4 million) by 18 November 2023 by The Economist, as well as over 18.5 million by 1 April 2023 by the Institute for Health Metrics and Evaluationand ≈18.2 million (earlier) deaths between 1 January 2020, and 31 December 2021, by a comprehensive international study.Such deaths include deaths due to healthcare capacity constraints and priorities, as well as reluctance to seek care (to avoid possible infection). Further research may help distinguish the proportions directly caused by COVID-19 from those caused by indirect consequences of the pandemic.
In May 2022, the WHO estimated the number of excess deaths by the end of 2021 to be 14.9 million compared to 5.4 million reported COVID-19 deaths, with the majority of the unreported 9.5 million deaths believed to be direct deaths due the virus, rather than indirect deaths. Some 
A December 2022 WHO study estimated excess deaths from the pandemic during 2020 and 2021, again concluding ≈14.8 million excess early deaths occurred, reaffirming and detailing their prior calculations from May as well as updating them, addressing criticisms. These numbers do not include measures like years of potential life lost and may make the pandemic 2021's leading cause of death.
The time between symptom onset and death ranges from 6 to 41 days, typically about 14 days. Mortality rates increase as a function of age. People at the greatest mortality risk are the elderly and those with underlying conditions.
==== Infection fatality ratio (IFR) ====
See also: List of human disease case fatality rates
IFR estimate per age group
Age group	IFR
0–34 	0.004%
35–44 	0.068%
45–54 	0.23%
55–64 	0.75%
65–74 	2.5%
75–84 	8.5%
85 + 	28.3%
The infection fatality ratio (IFR) is the cumulative number of deaths attributed to the disease divided by the cumulative number of infected individuals (including asymptomatic and undiagnosed infections and excluding vaccinated infected individuals). It is expressed in percentage points. Other studies refer to this metric as the infection fatality risk.
In November 2020, a review article in Nature reported estimates of population-weighted IFRs for various countries, excluding deaths in elderly care facilities, and found a median range of 0.24% to 1.49%. IFRs rise as a function of age (from 0.002% at age 10 and 0.01% at age 25, to 0.4% at age 55, 1.4% at age 65, 4.6% at age 75, and 15% at age 85). These rates vary by a factor of ≈10,000 across the age groups. For comparison, the IFR for middle-aged adults is two orders of magnitude higher than the annualised risk of a fatal automobile accident and much higher than the risk of dying from seasonal influenza.
In December 2020, a systematic review and meta-analysis estimated that population-weighted IFR was 0.5% to 1% in some countries (France, Netherlands, New Zealand, and Portugal), 1% to 2% in other countries (Australia, England, Lithuania, and Spain), and about 2.5% in Italy. This study reported that most of the differences reflected corresponding differences in the population's age structure and the age-specific pattern of infections. There have also been reviews that have compared the fatality rate of this pandemic with prior pandemics, such as MERS-CoV.
For comparison the infection mortality rate of seasonal flu in the United States is 0.1%, which is 13 times lower than COVID-19.
==== Case fatality ratio (CFR) ====
Another metric in assessing death rate is the case fatality ratio (CFR), which is the ratio of deaths to diagnoses. This metric can be misleading because of the delay between symptom onset and death and because testing focuses on symptomatic individuals.
Based on Johns Hopkins University statistics, the global CFR is 1.02 percent (6,881,955 deaths for 676,609,955 cases) as of 10 March 2023. The number varies by region and has generally declined over time.
== Disease ==
Main article: COVID-19
=== Variants ===
Main article: Variants of SARS-CoV-2
Several variants have been named by WHO and labelled as a variant of concern (VoC) or a variant of interest (VoI). Many of these variants have shared the more infectious D614G. As of May 2023, the WHO had downgraded all variants of concern to previously circulating as these were no longer detected in new infections. Sub-lineages of the Omicron variant (BA.1 - BA.5) were considered separate VoCs by the WHO until they were downgraded in March 2023 as no longer widely circulating.
=== Signs and symptoms ===
Main article: Symptoms of COVID-19