From the end of 2020, multiple variants of concern have emerged during the COVID-19 pandemic. Most recently, the Omicron variant has become dominant worldwide over other strains, with the potential for the emergence of other new variants or subvariants in the future. The Omicron variants have demonstrated increasing transmissibility and therefore are more challenging to control (Kraemer et al., 2021; World Health Organization, 2022). In general, increased transmissibility for a variant indicates an increased transmission strength, a higher transmission speed, or both.
