SARS‑CoV‑2 is the novel coronavirus responsible for coronavirus disease 2019 (COVID‑19), a respiratory illness first identified in Wuhan, China, in late 2019. It is an enveloped, positive‑sense, single‑stranded RNA virus belonging to the Betacoronavirus genus and lineage B.
Structure and Biology
SARS‑CoV‑2 has a genome of approximately 29.9 kilobases, encoding nonstructural proteins that form the replication–transcription complex and structural proteins including spike (S), envelope (E), membrane (M) and nucleocapsid (N). The virion is spherical with a lipid envelope about 80‑120 nm in diameter, with S proteins forming the characteristic corona‑like appearance. The S protein binds the human angiotensin‑converting enzyme 2 (ACE2) receptor; proteolytic activation by transmembrane serine protease 2 (TMPRSS2) facilitates membrane fusion and viral entry. Once internalized, the viral RNA is translated to produce polyproteins that are cleaved into nonstructural proteins for replication. New genomes and subgenomic mRNAs are synthesised in double‑membrane vesicles in the cytoplasm. Virions assemble at the endoplasmic reticulum–Golgi intermediate compartment and are released by exocytosis. The virus originated from a bat coronavirus, with a probable intermediate host yet to be conclusively identified. Its relatively high affinity for ACE2 and the ability to spread efficiently among humans distinguish it from other known coronaviruses. Clinical manifestations range from asymptomatic infection to severe pneumonia, acute respiratory distress syndrome and multi‑system inflammation; risk of severe disease increases with age and comorbidities.
Pandemic Spread and Variants
The emergence of SARS‑CoV‑2 in December 2019 led to an unprecedented global pandemic. By mid‑2025, more than 770 million confirmed cases and over 7 million deaths had been reported worldwide. Transmission occurs primarily via respiratory droplets, aerosols and close contact, with a basic reproduction number (R₀) initially estimated between 2 and 3. Public health responses, including physical distancing, mask wearing, diagnostic testing and vaccination, have been critical in reducing transmission. The virus evolves through mutations in the spike protein; several variants of concern have emerged, including Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2) and Omicron (B.1.1.529) and its sublineages. These variants differ in transmissibility, antigenicity and virulence, necessitating ongoing surveillance and vaccine updates. Vaccines based on mRNA, adenoviral vectors and inactivated virus platforms have been developed and deployed globally, dramatically reducing severe disease and mortality.
SARS‑CoV‑2 is a lineage B betacoronavirus that adapted to efficient human‑to‑human transmission and caused the COVID‑19 pandemic. Understanding its structure, receptor usage and evolutionary dynamics has informed the development of therapeutics and vaccines. Continued vigilance and global cooperation are essential to monitor emerging variants and mitigate future outbreaks.
Related Terms: SARS‑CoV, MERS‑CoV, COVID‑19, ACE2 receptor, Coronavirus variants