Pandemic coronavirus: an overview of SARS-CoV-2 and COVID-19 disease

A novel coronavirus has emerged in the human population every eight to 10 years of the 21st century. Severe acute respiratory syndrome coronavirus (SARS-CoV) was first noticed in 2002, while Middle Eastern Respiratory Syndrome coronavirus (MERS-CoV) was recognised in 2012. The latest one is severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of COVID-19.¹ This was first reported from China in December 2019 – although the first cases might have occurred in November – and has spread globally since January 2020. COVID-19 was declared a pandemic by the World Health Organization on 11 March 2020.¹

Virology

Coronaviruses are enveloped, positive-sense single-stranded RNA viruses. The name comes from the appearance of the viral particles under electron microscopy (Fig 1). Glycoprotein spikes (S proteins) are observed at the surface of the lipid envelope and, along with the overall pleomorphic shape (Fig 2), are reminiscent of the corona of the sun.² Thousands of coronaviruses have been recognised.³ In humans, two species (HCoV-229E and HCoV-OC43) were first identified in the 1960s. These are well-established in the population as causative agents of the common cold.⁴ Sporadic cases of respiratory infection have been attributed to two further species (HCoV-NL63 and HKU1) isolated and characterised in the mid-2000s.⁴ Coronaviruses associated with epidemic (SARS-CoV, MERS-CoV) and pandemic (SARS-CoV-2) transmission are betacoronaviruses (Table 1).