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 has been called COVID-19 (an acronym for coronavirus disease 2019). 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, some studies indicate that the virus remains stable for several hours to days in aerosols and on surfaces; thus, individuals may be acquiring the virus either via the air or after touching contaminated objects. Because of the many unknowns concerning this novel coronavirus and the rapidity with which it is spreading, health professionals and epidemiologists are extremely concerned. On January 30, 2020, the World Health Organization declared COVID-19 to be a global health emergency. On March 11, 2020, the World Health Organization officially announced that COVID-19 is a pandemic (worldwide epidemic). 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 when the virus is observed using an electron microscope. Fewer than ten 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: Middle East respiratory syndrome (MERS); Severe acute respiratory syndrome (SARS)
COVID-19 cases have been reported in almost all countries across the world. As of mid-October 2021, COVID-19 has been confirmed in more than 240,000,000 persons worldwide, and approximately 4,900,000 people have died. The United States leads the world in the number of confirmed coronavirus cases (more than 44,800,000 cases, including over 720,000 deaths). In addition, the numbers of deaths are significant in Brazil (more than 602,000 deaths), India (more than 452,000 deaths), and Mexico (more than 284,000 deaths). As a result, 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 are being implemented across the United States, throughout Europe, and elsewhere in attempts to halt the pace of community spreading of the virus. Furthermore, multiple airlines have temporarily suspended most international flights due to the coronavirus outbreak. Overall, airlines are adopting a series of measures to prevent the spread of the deadly disease. See also: Pneumonia; Respiratory system disorders
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 even death. Typical symptoms include cough, fever, shortness of breath, and breathing difficulties. Although further determinations are necessary, symptoms have appeared in as few as 2 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. However, COVID-19 is not the same as the coronavirus that causes either MERS or SARS. Despite this, preliminary genetic analyses suggest that the new virus emerged from a virus related to SARS. See also: Detection of respiratory viruses; Genetics
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 and is feeling unwell. The risk becomes more serious for those who are located in 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 can make some people very ill. More rarely, the disease can be fatal. Older people, and those with preexisting medical conditions (such as high blood pressure, heart problems, or diabetes), appear to be more vulnerable. Standard recommendations to prevent the spread of infection include regular hand washing, and covering 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.
Massive efforts are being undertaken by scientists and pharmaceutical companies around the world in order to develop a vaccine or specific antiviral therapies to prevent or treat COVID-19 infection. Until the disease is brought under full control, uninfected individuals (except for properly protected health-care professionals) need to avoid contact with afflicted persons. In general, those infected with COVID-19 should receive supportive treatment based on their clinical presentation—that is, to help relieve symptoms in relatively mild cases or to ensure respiratory function in the most severe cases. In December 2020, the United Kingdom, the European Union, and the United States granted emergency use authorization to a vaccine developed jointly by Pfizer in the United States and BioNTech in Germany. The Pfizer/BioNTech vaccine received full approval for use in the United States in late August 2021. In addition, another vaccine developed by Moderna in Cambridge, Massachusetts, was approved for emergency use in the United States as well. 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. Another effective vaccine developed by Johnson & Johnson in the United States was approved for emergency use in the United States in late February 2021. Various SARS-CoV-2 mutations have appeared as well, which may be more transmissible. For example, mutant strains of the coronavirus in India, South Africa, Brazil, and the United Kingdom are being 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) is highly contagious, being especially transmissible among unvaccinated individuals. So far, the approved vaccines have shown protection against the variants. See also: Critical care medicine; Searching for a COVID-19 vaccine