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 novel virus was first identified in the Chinese city of Wuhan in December 2019; a lockdown in Wuhan and other cities in surrounding Hubei failed to contain the outbreak, and it quickly spread to other parts of mainland China and around the world. The World Health Organization (WHO) declared a Public Health Emergency of International Concern on 30 January 2020, and a pandemic on 11 March 2020. Multiple variants of the virus have emerged and become dominant in many countries since 2021, with the Alpha, Beta, and Delta variants being the most virulent. As of 23 October 2021, more than 243 million cases and 4.94 million deaths have been confirmed, making it one of the deadliest pandemics in history. COVID-19 symptoms range from none to life-threatening. Severe illness is more likely in elderly patients and those with certain underlying medical conditions. Transmission of COVID-19 occurs 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 the virus can transmit over longer distances, particularly indoors and in poorly ventilated areas. Transmission can also occur, rarely, via contaminated surfaces or fluids. People remain contagious for up to 20 days, and can spread the virus even if they do not develop symptoms. Several vaccines have been approved and distributed in various countries, which have initiated mass vaccination campaigns since December 2020. Other recommended preventive measures include social distancing, wearing face masks in public, ventilation and air-filtering, covering one's mouth when sneezing or coughing, hand washing, disinfecting surfaces, and quarantining people who have been exposed or are symptomatic. 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, business closures, workplace hazard controls, testing protocols, and systems for tracing contacts of the infected. The pandemic has resulted in severe social and economic disruption around the world, including the largest global recession since the Great Depression in the 1930s. It has led to widespread supply shortages exacerbated by panic buying, agricultural disruption, and food shortages. The resultant near-global sustained quarantine saw an unprecedented decrease in the emission of pollutants. 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.