We directly compared all variants, showing that convalescence greater than 5 months post-symptom onset from ancestral computer virus provides little protection against SARS-CoV-2 variants. while a three-dose vaccine regimen provides over 50-fold enhanced protection against Omicron BA.1 compared to a two-dose. A novel Mab neutralizes Omicron BA.1 and BA.2 variants better than the clinically approved Mabs, although neither can neutralize Omicron BA.4 or BA.5. Thus, the need remains for continued vaccination-booster efforts, with development for vaccine and Mab improvement for broadly neutralizing activity. The usefulness of specific Mab applications links with the windows of clinical opportunity when a cognate viral variant is present in the infected populace. Keywords:SARS-CoV-2 variant, Omicron, neutralization assay, monoclonal antibody == 1. Introduction == SARS-CoV-2 was first recognized in the Lexibulin dihydrochloride western hemisphere near Seattle, Lexibulin dihydrochloride WA, USA, in January 2020. Since then, the computer virus has undergone quick genetic diversification leading to the progressive outgrowth of new computer virus strains underlying the pandemic coronavirus infectious disease 2019 (COVID-19) [1]. SARS-CoV-2 has CR1 shown amazing genomic diversification, achieving > 1500 unique Phylogenetic Assignment of Named Global Outbreak Lineages (PANGOLIN) [2]. Some variants have demonstrated increased transmissibility, virulence, and/or immune evasion and are Lexibulin dihydrochloride defined as variants of concern (VOC) [3]. The three vaccines Lexibulin dihydrochloride approved by the FDA for use in the United States all target the spike protein of the original ancestral SARS-CoV-2 [4]. The neutralizing antibody responses and vaccine effectiveness gradually decline after vaccination and are less effective against emerging VOC [5,6,7,8,9,10]. The mRNA-based vaccine boosters can enhance neutralizing immunity [6,11,12]. Even though viral dynamics of the VOC infections are comparable between vaccinated and unvaccinated persons [13], the effectiveness of immunity from previous infection with the non-Omicron computer virus to prevent reinfection has been substantially lower for the Omicron VOC (56%) compared to the alpha (90%), beta (86%), and delta (92%) variants, indicating differences in immune evasion across these VOC [14]. Consistent with a more considerable immune escape, a study of household SARS-CoV-2 transmission showed higher transmission for Omicron than delta for fully vaccinated adults [15]. These epidemiological results closely match results from immunogenicity studies showing high levels of escape from neutralizing antibody immunity for Omicron subvariants [16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31]. As humoral immunity is currently the hallmark for protection against SARS-CoV-2 contamination, we as well as others have focused on developing human monoclonal antibodies (Mabs) as leverage in immune therapeutics to treat contamination [32,33,34,35]. In particular, therapeutic monoclonal antibodies are useful for treating high-risk and severe COVID-19 patients [36]. We have recognized a panel of monoclonal antibodies with neutralizing activity against ancestral SARS-CoV-2 [35]. Here we present a first side-by-side analysis of the extent of humoral immune protection against SARS-CoV-2 variants from convalescent sera following recovery from ancestral computer virus infection. We also assess novel Mabs for neutralization of emerging SARS-CoV-2 Omicron variants. Our studies reveal a continual need for vaccine applications and the development of Mab therapeutics against contemporary SARS-CoV-2 variants for immune protection against a progressing pandemic. == 2. Materials and Methods == == 2.1. Isolation of SARS-CoV-2 Variants from Clinical Samples == SARS-CoV-2 specimens were collected by the University or college of Washington Virology Laboratory. To generate P0 stock, the samples were filtered through Corning Costar Spin-X centrifuge tube filter (CLS8160), and 0.1 mL was used to infect Vero E6 cells ectopically expressing human Ace2 and TMPRSS2 (a gift from Dr. Barney Graham, National Institutes of Health, Bethesda MD) in a 48-well plate. P1 computer virus stock cultures were produced in Vero E6/TMPRSS2 cells (JCRB1819) and tittered as explained [37,38]. Lexibulin dihydrochloride == 2.2. Sequencing == An aliquot of P1 stock was subject to RNA extraction (Zymo Research, R1040) and sequencing using the Swift SARS-CoV148 2 SNAP Version 2.0 kit (Swift Biosciences, Ann Arbor, MI, USA) on Illumina NextSeq 500 (Illumina, San Diego, CA, USA). Consensus genome sequences were generated through a covid-swift-pipeline (https://github.com/greninger-lab/covid_swift_pipeline, accessed on 11 May 2021), and the lineages were assigned based on the Pangolin dynamic lineage nomenclature plan [39]. == 2.2.1..