Omicron-B.1.1.529: Striking Immune Evasion but Causing Less Severe Disease than Delta

A new mutated version of SARS-COV-2 virus was detected near the end of November 2021, in South Africa. The lineage was called B.1.1.529 (or BA.1) (or Nextstrain clade 21K). World Health Organization (WHO) labelled it as ‘Omicron’ and later on declared it as a Variant of Concern (VOC). The Omicron variant, the fifth VOC, accumulated a large number of mutations in its Spike region which is considered to be the most identified mutations in any COVID-19 VOC so far. The most urgent question that arose was if these mutations cause immune evasion to current vaccineinduced immunity or prior infections. In the previous article, we describe the newly identified Omicron VOC (Khandelwal and Yau, 2021). In this article, we present a comprehensive review on Omicron BA.1, with a special focus on its immunity evasion and the impact of disease severity caused by it based on current available data and publications.