Variants of SARS-CoV-2

Variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are viruses that, while similar to the original, have genetic changes that are of enough significance to lead virologists to label them separately. SARS-CoV-2 is the virus that causes coronavirus disease 2019 (COVID-19). Some have been stated to be of particular importance, due to their potential for increased transmissibility, increased virulence, or reduced effectiveness of vaccines against them. These variants contribute to the continued circulation of SARS-CoV-2.

As of 25 June 2025, the variants of interest as specified by the World Health Organization are JN.1, and the variants under monitoring are KP.3, KP.3.1.1, JN.1.18, LP.8.1, NB.1.8.1, XEC and XFG.

Overview

The origin of SARS-CoV-2 has not been identified. However, the emergence of SARS-CoV-2 may have resulted from recombination events between a bat SARS-like coronavirus and a pangolin coronavirus through cross-species transmission. The earliest available SARS-CoV-2 viral genomes were collected from patients in December 2019, and Chinese researchers compared these early genomes with bat and pangolin coronavirus strains to estimate the ancestral human coronavirus type; the identified ancestral genome type was labeled "S", and its dominant derived type was labeled "L" to reflect the mutant amino acid changes. Independently, Western researchers carried out similar analyses but labeled the ancestral type "A" and the derived type "B". The B-type mutated into further types including B.1, which is the ancestor of the major global variants of concern, labeled in 2021 by the WHO as alpha, beta, gamma, delta and omicron variants.

Early in the pandemic, the relatively low number of infections (compared with later stages of the pandemic) resulted in fewer opportunities for mutation of the viral genome and, therefore, fewer opportunities for the occurrence of differentiated variants.