Omicron BA.2 Lineage, the "Stealth" Variant: Is It Truly a Silent Epidemic? A Literature Review

The epidemic curve of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is silently rising again. Worldwide, the dominant SARS-CoV-2 variant of concern (VOC) is Omicron, and its virological characteristics, such as transmissibility, pathogenicity, and resistance to both vaccine- and infection-induced immunity as well as antiviral drugs, are an urgent public health concern. The Omicron variant has five major sub-lineages; as of February 2022, the BA.2 lineage has been detected in several European and Asian countries, becoming the predominant variant and the real antagonist of the ongoing surge. Hence, although global attention is currently focused on dramatic, historically significant events and the multi-country monkeypox outbreak, this new epidemic is unlikely to fade away in silence. Many aspects of this lineage are still unclear and controversial, but its apparent replication advantage and higher transmissibility, as well as its ability to escape neutralizing antibodies induced by vaccination and previous infection, are rising global concerns. Herein, we review the latest publications and the most recent available literature on the BA.2 lineage of the Omicron variant.