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COVID-19: from the structure and replication cycle of SARS-CoV-2 to its disease symptoms and treatment.

In December 2019, a small number of cases of pneumonia of unknown origin were recognized in the city of Wuhan, China. Soon, the disease, whose etiological factor was recognized as a coronavirus SARS-CoV-2, had spread across the world. The resulting CoV-associated diseases were classified by the WHO as COVID-19, and a pandemic was declared in March 2020. By 25 November 2021, there have been nearly 256.8 million of confirmed cases of COVID-19 around the world, including 5.17 million deaths. This review focuses on basal characteristics of the SARS-CoV-2 virus - its structure, replication cycle, variants and course of infection. It also briefly characterizes the currently recommended drugs and vaccines. Coronaviruses (CoVs) are a group of RNA viruses with a characteristic solar corona image observable on electron micrographs. SARS-CoV-2 possesses high affinity to human angiotensin converting enzyme 2 (ACE2) which serves as a cellular entry receptor. Its replication in human cells is accompanied by a high mutation rate. Six variants of SARS-CoV-2 have been found to be associated with essential changes of global public health significance; they are referred to as 'variants of concern' (VOC). The main route of transmission is through respiratory droplets. Although COVID-19 presents primarily as a respiratory disease, it can affect various other organs and systems that present the ACE2 protein to which the virus binds, including the heart, kidneys, intestines, liver, muscular and nervous system. COVID-19 infection can result in uncontrolled systemic hyperinflammation caused by release of a large amount of pro-inflammatory cytokines (a 'cytokine storm'), which can lead to multi-organ failure, rapid clinical deterioration and even death. Around 30% of those infected with SARS-CoV-2 remain asymptomatic, with the majority of patients demonstrating only mild or moderate symptoms; however, about 20% develop severe or critical disease. Three main groups of medications are currently recommended for therapy of COVID-19: monoclonal antibodies against the S protein of SARS-CoV-2, antiviral drugs and immunosuppressants which inhibit the cytokine storm. At present, the safest and most cost-effective way to prevent COVID-19 illness is a preventative vaccination.