Inactivated SARS-CoV-2 Variant Kappa, Lineage B.1.617.1 (USA/CA-Stanford-15_S02/2021)

Since its emergence in late 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for the current COVID-19 pandemic, has evolved several new viral variants of concern (VOCs) and variants of interest (VOIs). SARS-CoV-2 enters host cells by binding to angiotensin-converting enzyme 2 (ACE2), a binding mechanism that varies between species. For example, ACE2 in mice, New World monkeys, and koalas does not effectively bind to the SARS-CoV-2 spike protein, hindering viral entry into these species. Furthermore, mutations in the spike protein, a target for vaccines and therapeutic antibodies, could alter SARS-CoV-2''s transmission, host tropism, pathogenicity, and susceptibility to vaccine-induced antibodies. For example, the D614G mutation, discovered early in the pandemic, promotes spike binding to ACE2, thereby enhancing viral transmission. Subsequently, the N501Y mutation found in the spike protein of strains B.1.1.7, B.1.351, and B.1.1.28.1 increases the binding affinity between the receptor binding domain (RBD) and ACE2, thereby enhancing viral adaptability and infectivity.

In 2021, India experienced a sharp rise in COVID-19 cases and deaths, and the increased spread of the virus has been linked to the newly discovered SARS-CoV-2 variants B.1.617 and B.1.618, which harbor mutations in their spike proteins. B.1.617.1 (kappa) harbors an E154K mutation in the spike protein N-terminal domain (NTD), L452R and E484Q mutations in the spike protein RBD, and a P681R mutation near the furin cleavage site. It has been designated a variant of concern (VOI) by the World Health Organization (WHO). The B.1.617.2 (Delta) virus has the L452R and T478K mutations in the spike protein receptor binding domain (RBD), as well as the P681R mutation, and has been designated a VOC. The B.1.618 virus has the Δ145–146 (deletion of residues 145 and 146) and E484K mutations in the nucleoside triphosphate (NTD) and receptor binding domain (RBD), respectively. Indeed, some mutations in the Kappa, Delta, and B.1.618 viruses have been found in other variants. For example, the L452R mutation has been found in the B.1.427 and B.1.429 variants, both of which are associated with increased infectivity and reduced susceptibility to vaccine-induced antibodies. The T478K mutation has been found in the Mexican variant, B.1.1.519.