A newly identified coronavirus, provisionally termed 2019-nCoV (an acronym for 2019 novel coronavirus) and subsequently named "severe acute respiratory syndrome coronavirus 2" (SARS-CoV-2), emerged in central China in November 2019. The disease caused by this virus, called COVID-19 (an acronym for "coronavirus disease 2019"), is currently a pandemic (worldwide epidemic) that has sickened and killed millions of people around the world. The infectious virus initially affected individuals in the city of Wuhan, predominantly those working at or frequenting certain animal markets. At first, the virus was thought to spread from animals (possibly bats or pangolins) to people. However, affected individuals who did not have exposure to any animal markets were subsequently identified, indicating that person-to-person transmission was occurring. In addition, studies indicated that the virus remains stable for several hours to days in aerosols and on surfaces; thus, individuals can acquire the virus either via the air or after touching contaminated objects. The many initial unknowns regarding this novel coronavirus and the rapidity with which it is spread prompted the World Health Organization (WHO) to declare COVID-19 a global health emergency on January 30, 2020. On March 11, 2020, the WHO officially announced that COVID-19 was a pandemic. See also: Animal virus; Coronavirus; Disease ecology; Epidemic; Epidemiology; Infectious disease; Virus; Virus classification
Coronaviruses comprise a major group of common animal viruses that typically infect mammals and birds. The name coronavirus (Latin corona, meaning crown or a halo appearance) comes from the shape of the virus seen when observing the virus using an electron microscope. Fewer than 10 coronaviruses have been determined to cause disease in humans. In the twenty-first century, though, a few emergent coronaviruses have resulted in serious and contagious diseases—especially pneumonia or other respiratory illnesses—in humans. Two of the most significant coronavirus diseases are severe acute respiratory syndrome (SARS), which was initially reported in Asia in 2003 and affected more than 8000 people (with 774 deaths), and Middle East respiratory syndrome (MERS), which was first reported in Saudi Arabia in 2012 and affected more than 2500 individuals (including at least 860 deaths). See also: Electron microscope; Middle East respiratory syndrome (MERS); Pneumonia; Severe acute respiratory syndrome (SARS)
COVID-19 cases have been reported in almost all countries across the world. As of early December 2021, COVID-19 was confirmed in more than 260,000,000 persons worldwide, and approximately 5,200,000 people have died, according to the WHO. The United States leads the world in the number of confirmed coronavirus cases with more than 47,900,000 cases, including over 773,000 deaths. In addition, the numbers of deaths are significant in Brazil (more than 614,000 deaths), India (more than 468,000 deaths), and Mexico (more than 293,000 deaths). As a result of the disease's severity, many countries have ordered lockdowns and closed their borders, and individuals (especially those persons most at risk, such as the elderly) have been encouraged to self-quarantine. Urgent emergency measures have been implemented across the United States, throughout Europe, and elsewhere in attempts to halt the pace of the community spread of the virus. Furthermore, multiple airlines have at times suspended international flights due to the coronavirus outbreak.
Individuals infected by COVID-19 have displayed a wide spectrum of symptoms, ranging from mild cold- or flu-like illness to severe respiratory distress and death. Typical symptoms include cough, fever, shortness of breath, and breathing difficulties. Symptoms have generally appeared in as few as two days or as long as 14 days after exposure to the coronavirus. This range is similar to that observed for the incubation period of MERS viruses. See also: Detection of respiratory viruses; Fever; Respiratory system; Respiratory system disorders
The chance of contracting COVID-19 is low for individuals who are not located in an area where COVID-19 is spreading, or for those who have not traveled from one of those areas or have not been in close contact with someone who has traveled from such an area and is feeling unwell. The risk becomes more serious for those who are an area where an outbreak of COVID-19 is occurring. Such individuals should follow advice issued by national and local health authorities. Although COVID-19 causes only mild illness for most people, the virus does make some people very ill. More rarely, the disease is fatal. Older people, and those with preexisting medical conditions [such as high blood pressure (hypertension), heart problems, or diabetes], are more likely to have severe outcomes. Standard recommendations to prevent the spread of infection include wearing facial masks when indoors, regular hand washing, and covering one's mouth and nose when coughing and sneezing. Avoidance of close contact with anyone showing symptoms of respiratory illness, especially coughing and sneezing, is important as well. See also: Cardiovascular system; Critical care medicine; Diabetes; Heart disorders; Hypertension
Massive efforts have been undertaken by scientists and pharmaceutical companies around the world in order to develop vaccines and specific antiviral therapies to prevent or treat COVID-19 infection. There are currently three available vaccines in the United States, made by Pfizer-BioNTech, Moderna, and Johnson & Johnson. The U.S. Centers for Disease Control and Prevention (CDC) considers each vaccine safe and effective. The Pfizer/BioNTech vaccine received full approval for use in the United States in late August 2021; the Moderna vaccine was approved for emergency use in December 2020; and the Johnson & Johnson vaccine was approved for emergency use in late February 2021. Moreover, a vaccine developed by AstraZeneca and Oxford University was granted emergency use approval in the United Kingdom in late December 2020 and in the European Union in late January 2021. In addition to vaccines, various treatments have also been developed or been found to be effective in improving clinical outcomes for COVID-19 patients. The use of corticosteroids, for example, can reduce damaging multisystem inflammation triggered by the virus. Other treatments include administration of the antiviral drug remdesivir, convalescent plasma rich in antibodies from previously infected individuals, and pharmaceutically manufactured monoclonal antibodies. See also: Antibody; Immunology; Inflammation; Monoclonal antibodies; Pharmacology; Searching for a COVID-19 vaccine; Serology; Vaccination
Various SARS-CoV-2 mutations have appeared and which have resulted in more transmissible and/or more virulent variants of the original novel coronavirus. For example, mutant strains of the coronavirus in India, South Africa, Brazil, and the United Kingdom have been evaluated and tracked closely by epidemiologists because these strains have been detected in other locations around the world. In particular, the mutant Delta variant (B.1.617.2, which originated in India) has proven highly contagious, being especially transmissible among unvaccinated individuals. So far, the approved vaccines have shown protection against the variants. See also: Mutation