Another coronavirus that circulated in China in 2003 caused a more dangerous condition known as Severe Acute Respiratory Syndrome, or SARS. The virus was contained after it had sickened 8,098 people and killed 774. Middle East Respiratory Syndrome, or MERS, first reported in Saudi Arabia in 2012, is also caused by a coronavirus. The new virus has been named SARS-CoV-2. The disease it causes is called Covid-19.
Many forms are relatively unremarkable, characterized by a particular assortment of mutations. But scientists have been holding close watch on three rapidly evolving varieties that include an odd constellation of mutations, first identified in the UK, South Africa, and Brazil. They also share a mutation called N501Y that inhibits the spike protein's receptor binding domain (RBD), which is used by the virus to clasp and reach the receptors of human cells. The mutation replaces the 501st amino acid, asparagine, of SARS-CoV-2 with tyrosine, theoretically enabling it to bind more closely to ACE2 receptors, cell studies and animal models indicate.
A new strain of coronavirus that has not been previously identified in humans is SARS-CoV-2. The United States Centers for Disease Control and Prevention reports that signs can occur in as little as 2 days or as long as 14 days after exposure, but the incubation time of this strain is currently uncertain. Chinese researchers have suggested that during its incubation time, SARS-CoV-2 could be contagious.