COVID-19, contagious viral disease caused by severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2, a coronavirus that is genetically related to SARS-CoV, which causes SARS. Symptoms generally develop between 2 and 14 days after exposure, with many persons showing symptoms after 5 days. Although some infected individuals may experience no or very mild symptoms, patients typically may have a fever, dry cough, a sudden loss of smell or taste, and shortness of breath or difficulty breathing. Some patients experience chills (in some cases with shaking), body aches, headache, fatigue, a sore throat, and nausea, vomiting, or diarrhea. More serious illness may progress to pneumonia, unusual blood thickening and clotting, heart failure and arrhythmia, and acute respiratory distress syndrome. Persons who are 60 or older or who have such underlying medical conditions as heart or lung disease, diabetes, obesity, or certain cancers, are at higher risk for developing more serious complications and dying from the disease. Although children generally have a less severe response to the infection, in rare cases children who have been infected or been around infected persons have developed pediatric multisystem inflammatory syndrome, which is marked by fever, abdominal pain, vomiting, diarrhea, fatigue, rash, bloodshot, or other symptoms and may involve the heart, lungs, kidneys, brain, skin, eyes, or gastrointestinal organs. Many recovered patients continue to experience fatigue, difficulty in concentrating, and other after-effects.

Treatment consists of medication that can alleviate the symptoms and other supportive care; the antiviral remdesivir may shorten recovery time by several days, and some corticosteroids have been found to improve survival rates for severely ill patients. Monoclonal antibody treatments have been authorized on an emergency basis to treat mild to moderate cases, and blood plasma from recovered patients, which contains antibodies to the virus, has also been used on an emergency basis to treat the severely ill. Significant and rapid research into a potential cure or vaccine led to the experimental or emergency use of several vaccines by late 2020. Measures such as wearing masks, physical distancing, cleaning hands and surfaces, and quarantine are relied on to control transmission because the virus is spread by droplets produced by coughing or through contact with contaminated surfaces. COVID-19 is generally less severe and less deadly than SARS and MERS, with many studies estimating that the actual fatality rate (as opposed to that based on reported cases) is between .5% to 1%, but the virus has proved especially deadly in nursing home settings, and rapid increases in the number of serious cases in some regions have overwhelmed hospitals at times.

As with SARS and MERS, COVID-19 is believed to be caused by a bat coronavirus that spread to humans, but it is unclear how SARS-CoV-2 was transferred. First identified in Wuhan, China, in Dec., 2019, COVID-19 was initially downplayed by local officials and soon became epidemic in China, greatly surpassing the number of cases that occurred in the SARS outbreak (2002–3). The Chinese government publicly acknowledged the seriousness of the epidemic in late Jan., 2020, after the disease was identified in a traveler to Thailand, and the rapid spread of virus led the World Health Organization to declare a global public health emergency at the end of the month. China quarantined Hubei, province where Wuhan is located, as well as a number of other locations, with significant economic impacts.

Despite travel restrictions and spot quarantine efforts by other countries, COVID-19 gradually spread worldwide. Many nations also were initially slow to respond, but most ultimately instituted a range of restrictive public health measures in an attempt to constrain the disease's further spread. Studies have suggested that the disease in fact spread earlier and unnoticed before travel restrictions were in place. By April the disease had had significant health and economic impacts worldwide, especially in Western Europe, Iran, and the United States. The last had the highest number of reported cases and deaths, with the greater New York City area the site of the worst outbreak. As the year progressed, the worst hit nations were the United States, India, and Brazil, all of which generally instituted less restrictive control measures for shorter periods of time.

In early 2021, several new vaccines were introduced on an emergency basis, with the one-third of the population in the US having received at least one dose of a vaccine by the end of March; vaccination rates have been slower in the rest of the world. However, new variants of the disease—notably in the United Kingdom, South Africa, and Brazil—developed that appear to be more contagious than the original virus and perhaps are more lethal as well. The UK returned to a full shutdown in late 2020 to battle the rapidly spreading variant, followed by Germany and France in early 2021. Variants have subsequently been found in other parts of the world, including the United States, including the so-called Delta (which became the dominant form of the disease in 2021) and Omicron variants, both highly contagious.

In Dec. 2021, Omicron spread rapidly in the United States and major European countries and became the dominant strain across the world by early 2022. By Jan. 2022, new cases rose to a seven-day average of around 750,000 in the United States with an average of 2.5 million cases worldwide, both rapidly increasing. Total reported cases exceeded 61.5 million and deaths exceeded 825,000 in the United States. At the same, cases worldwide reached 290 million and deaths exceeded 5.5 million.

The economic effects of COVID-19, due to the measures used to control its spread and to the efforts taken by people to avoid becoming infected, led to the world's worst economic crisis since the Great Depression. The world economy, which the International Monetary fund had predicted to grow by 2.5% in 2020, shrank by 4.3%. Tens of millions lost their jobs, some only temporarily but others permanently. Increased government spending on unemployment benefits and on aid to businesses helped mitigate some of the economic effects in varying degrees internationally, but also dramatically increased government deficits and public debt.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.

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