The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus was first identified in December 2019 in Wuhan, China. The World Health Organization declared a Public Health Emergency of International Concern regarding COVID-19 on 30 January 2020, and later declared a pandemic on 11 March 2020. As of 4 June 2021, more than 172 million cases have been confirmed, with more than 3.7 million confirmed deaths attributed to COVID-19, making it one of the deadliest pandemics in history.
coronavirus 2 (SARS‑CoV‑2)[a]
(1 year, 6 months and 4 days)
Symptoms of COVID-19 are highly variable, ranging from none to life-threateningly severe. COVID-19 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 they can be inhaled 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 developed and widely distributed since December 2020. Current 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. Numerous jurisdictions have also worked to increase testing capacity and trace contacts of the infected.
The pandemic has resulted in significant 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, and food shortages. However, there have also been decreased emissions of pollutants and greenhouse gases. 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.
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 continue to experience a range of effects for months after recovery—named 
The virus is transmitted mainly via the respiratory route, when people inhale droplets and particles that infected people release as they breathe, talk, cough, sneeze or sing. The closer people interact, and the longer they interact, the more likely they are to transmit COVID-19, but infection can occur over longer distances, particularly indoors. People are at their peak of infectiousness when their symptoms start, and are infectious for up to 3 days prior to this. Their infectiousness declines after the first week, but they remain contagious for up to 20 days, and can spread the virus even if they never developed any symptoms.
The size of the infectious particles is on a continuum, ranging from small airborne particles that remain suspended in the air for long periods, to larger droplets that may remain airborne or fall to the ground. This continuum between droplets and aerosols has redefined the traditional understanding of how respiratory viruses transmit. The largest droplets of respiratory fluid do not travel far, and can be inhaled, or land on mucous membranes on the eyes, nose, or mouth to cause new infection. The fine aerosol particles are in highest concentration when people are in close proximity, leading to the virus transmitting easier when people are physically close. However, airborne transmission does occur at longer distances, mainly in locations that are poorly ventilated (such as restaurants, choirs, gyms, nightclubs, offices, and religious venues). In those conditions small particles can remain suspended in the air for minutes to hours.
The number of people generally infected by one infected person varies; with only 10 to 20% of people responsible for the diseases spread. However, in September 2020 it was estimated that one infected person will, as a crude average, infect between two and three other people. This is more infectious than influenza, but less so than measles. It often spreads in clusters, where infections can be traced back to an index case or geographical location. There is a major role of "super-spreading events", where many people are infected by one person.It is possible that a person might get COVID-19 indirectly by touching a contaminated surface or object before touching their own mouth, nose, or eyes, though strong evidence suggests this does not contribute substantially to new infections. Although it is considered possible, there is no direct evidence of the virus being transmitted by skin to skin contact. The virus is not known to spread through feces, urine, breast milk, food, wastewater, drinking water, or via animal disease vectors (although some animals can contract the virus from humans). It very rarely transmits from mother to baby during pregnancy.
SARS‑CoV‑2 belongs to the broad family of viruses known as coronaviruses. It is a positive-sense single-stranded RNA (+ssRNA) virus, with a single linear RNA segment. Coronaviruses infect humans, other mammals, and avian species, including livestock and companion animals. Human coronaviruses are capable of causing illnesses ranging from the common cold to more severe diseases such as Middle East respiratory syndrome (MERS, fatality rate ~34%). SARS-CoV-2 is the seventh known coronavirus to infect people, after 229E, NL63, OC43, HKU1, MERS-CoV, and the original SARS-CoV.Viral genetic sequence data can provide critical information about whether viruses separated by time and space are likely to be epidemiologically linked. With a sufficient number of sequenced genomes, it is possible to reconstruct a phylogenetic tree of the mutation history of a family of viruses. By 12 January 2020, five genomes of SARS‑CoV‑2 had been isolated from Wuhan and reported by the Chinese Center for Disease Control and Prevention (CCDC) and other institutions; the number of genomes increased to 42 by 30 January 2020. A phylogenetic analysis of those samples showed they were "highly related with at most seven mutations relative to a common ancestor", implying that the first human infection occurred in November or December 2019. As of 7 May 2020,[update] 4,690 SARS‑CoV‑2 genomes sampled on six continents were publicly available.[clarification needed]
Preventive measures to reduce the chances of infection include getting vaccinated, staying at home, wearing a mask in public, avoiding crowded places, keeping distance from others, ventilating indoor spaces, managing potential exposure durations, washing hands with soap and water often and for at least twenty seconds, practising good respiratory hygiene, and avoiding touching the eyes, nose, or mouth with unwashed hands.Those diagnosed with COVID-19 or who believe they may be infected are advised by the CDC to stay home except to get medical care, call ahead before visiting a healthcare provider, wear a face mask before entering the healthcare provider's office and when in any room or vehicle with another person, cover coughs and sneezes with a tissue, regularly wash hands with soap and water and avoid sharing personal household items.
In Phase III trials, several COVID‑19 vaccines have demonstrated efficacy as high as 95% in preventing symptomatic COVID‑19 infections. As of April 2021[update], 16 vaccines are authorized by at least one national regulatory authority for public use: three RNA vaccines (Pfizer–BioNTech and Moderna), seven conventional inactivated vaccines (BBIBP-CorV, CoronaVac, Covaxin, WIBP-CorV, CoviVac, Minhai-Kangtai and QazVac), five viral vector vaccines (Sputnik Light, Sputnik V, Oxford–AstraZeneca, Convidecia, and Johnson & Johnson), and two protein subunit vaccines (EpiVacCorona and RBD-Dimer).[failed verification] In total, as of March 2021[update], 308 vaccine candidates are in various stages of development, with 73 in clinical research, including 24 in Phase I trials, 33 in Phase I–II trials, and 16 in Phase III development.Many countries have implemented phased distribution plans that prioritize those at highest risk of complications, such as the elderly, and those at high risk of exposure and transmission, such as healthcare workers. Single dose interim use is under consideration in order to extend vaccination to as many people as possible until vaccine availability improves.
On 21 December 2020, the European Union approved the Pfizer BioNTech vaccine. Vaccinations began to be administered on 27 December 2020. The Moderna vaccine was authorized on 6 January 2021 and the AstraZeneca vaccine was authorized on 29 January 2021.
On 4 February 2020, US Secretary of Health and Human Services Alex Azar published a notice of declaration under the Public Readiness and Emergency Preparedness Act for medical countermeasures against COVID-19, covering "any vaccine, used to treat, diagnose, cure, prevent, or mitigate COVID-19, or the transmission of SARS-CoV-2 or a virus mutating therefrom", and stating that the declaration precludes "liability claims alleging negligence by a manufacturer in creating a vaccine, or negligence by a health care provider in prescribing the wrong dose, absent willful misconduct". The declaration is effective in the United States through 1 October 2024. On 8 December it was reported that the AstraZeneca vaccine is about 70% effective, according to a study.
There is no specific, effective treatment or cure for coronavirus disease 2019 (COVID-19), the disease caused by the SARS-CoV-2 virus. Thus, the cornerstone of management of COVID-19 is supportive care, which includes treatment to relieve symptoms, fluid therapy, oxygen support and prone positioning as needed, and medications or devices to support other affected vital organs.
Most cases of COVID-19 are mild. In these, supportive care includes medication such as paracetamol or  body aches, cough), proper intake of fluids, rest, and nasal breathing. Good personal hygiene and a healthy diet are also recommended. The U.S. Centers for Disease Control and Prevention (CDC) recommend that those who suspect they are carrying the virus isolate themselves at home and wear a face mask.
People with more severe cases may need treatment in hospital. In those with low oxygen levels, use of the dexamethasone is strongly recommended, as it can reduce the risk of death. Noninvasive ventilation and, ultimately, admission to an intensive care unit for mechanical ventilation may be required to support breathing. Extracorporeal membrane oxygenation (ECMO) has been used to address the issue of respiratory failure, but its benefits are still under consideration.
Several experimental treatments are being actively studied in clinical trials. Others were thought to be promising early in the pandemic, such as hydroxychloroquine and lopinavir/ritonavir, but later research found them to be ineffective or even harmful. Despite ongoing research, there is still not enough high-quality evidence to recommend so-called early treatment. Nevertheless, in the United States, two monoclonal antibody-based therapies are available for early use in cases thought to be at high risk of progression to severe disease. The antiviral remdesivir is available in the U.S., Canada, Australia, and several other countries, with varying restrictions; however, it is not recommended for people needing mechanical ventilation, and is discouraged altogether by the World Health Organization (WHO), due to limited evidence of its efficacy.
- B.1.1.7, first detected in the UK, which has spread to over 120 countries
- P.1, first detected in Brazil, which has spread to more than 50 countries
- B.1.351, first detected in South Africa, which has spread to over 80 countries
Speed and scale are key to mitigation, due to the fat-tailed nature of pandemic risk and the exponential growth of COVID-19 infections. For mitigation to be effective, (a) chains of transmission must be broken as quickly as possible through screening and containment, (b) health care must be available to provide for the needs of those infected, and (c) contingencies must be in place to allow for effective rollout of (a) and (b).
Screening, containment and mitigation
Strategies in the control of an outbreak are screening, containment (or suppression), and mitigation. Screening is done with a device such as a thermometer to detect the elevated body temperature associated with fevers caused by the infection. Containment is undertaken in the early stages of the outbreak and aims to trace and isolate those infected as well as introduce other measures to stop the disease from spreading. When it is no longer possible to contain the disease, efforts then move to the mitigation stage: measures are taken to slow the spread and mitigate its effects on the healthcare system and society. A combination of both containment and mitigation measures may be undertaken at the same time. Suppression requires more extreme measures so as to reverse the pandemic by reducing the basic reproduction number to less than 1.
Part of managing an infectious disease outbreak is trying to delay and decrease the epidemic peak, known as flattening the epidemic curve. This decreases the risk of health services being overwhelmed and provides more time for vaccines and treatments to be developed. Non-pharmaceutical interventions that may manage the outbreak include personal preventive measures such as hand hygiene, wearing face masks, and self-quarantine; community measures aimed at physical distancing such as closing schools and cancelling mass gathering events; community engagement to encourage acceptance and participation in such interventions; as well as environmental measures such surface cleaning. Some measures, particularly those that focus on cleaning surfaces rather than preventing airborne transmission, have been criticized as hygiene theatre.
More drastic actions aimed at containing the outbreak were taken in China once the severity of the outbreak became apparent, such as quarantining entire cities and imposing strict travel bans. Other countries also adopted a variety of measures aimed at limiting the spread of the virus. South Korea introduced mass screening and localised quarantines and issued alerts on the movements of infected individuals. Singapore provided financial support for those infected who quarantined themselves and imposed large fines for those who failed to do so. Taiwan increased face mask production and penalised the hoarding of medical supplies.
Simulations for Great Britain and the United States show that mitigation (slowing but not stopping epidemic spread) and suppression (reversing epidemic growth) have major challenges. Optimal mitigation policies might reduce peak healthcare demand by two-thirds and deaths by half, but still result in hundreds of thousands of deaths and overwhelmed health systems. Suppression can be preferred but needs to be maintained for as long as the virus is circulating in the human population (or until a vaccine becomes available), as transmission otherwise quickly rebounds when measures are relaxed. Long-term intervention to suppress the pandemic has considerable social and economic costs.
Contact tracing is an important method for health authorities to determine the source of infection and to prevent further transmission. The use of location data from mobile phones by governments for this purpose has prompted privacy concerns, with Amnesty International and more than a hundred other organisations issuing a statement calling for limits on this kind of surveillance.
Several mobile apps have been implemented or proposed for voluntary use, and as of 7 April 2020 more than a dozen expert groups were working on privacy-friendly solutions such as using Bluetooth to log a user's proximity to other cellphones. (Users are alerted if they have been near someone who subsequently tests positive.)
On 10 April 2020, Google and Apple jointly announced an initiative for privacy-preserving contact tracing based on Bluetooth technology and cryptography. The system is intended to allow governments to create official privacy-preserving coronavirus tracking apps, with the eventual goal of integration of this functionality directly into the iOS and Android mobile platforms. In Europe and in the U.S., Palantir Technologies is also providing COVID-19 tracking services.
Increasing capacity and adapting healthcare for the needs of COVID-19 patients is described by the WHO as a fundamental outbreak response measure. The ECDC and the European regional office of the WHO have issued guidelines for hospitals and primary healthcare services for shifting of resources at multiple levels, including focusing laboratory services towards COVID-19 testing, cancelling elective procedures whenever possible, separating and isolating COVID-19 positive patients, and increasing intensive care capabilities by training personnel and increasing the number of available ventilators and beds. In addition, in an attempt to maintain physical distancing, and to protect both patients and clinicians, in some areas non-emergency healthcare services are being provided virtually.
Due to capacity limitations in the standard supply chains, some manufacturers are 3D printing healthcare material such as nasal swabs and ventilator parts. In one example, when an Italian hospital urgently required a ventilator valve, and the supplier was unable to deliver in the timescale required, a local startup received legal threats due to alleged patent infringement after reverse-engineering and printing the required hundred valves overnight. On 23 April 2020, NASA reported building, in 37 days, a ventilator which is currently undergoing further testing. NASA is seeking fast-track approval.