In-depth characterization of the BA.2 versus BA.1 variant


In a latest examine printed within the journal Nature, researchers evaluated the pathogenicity and infectivity of extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron BA.2 variant in hamsters and mice.

The emergence of the Omicron BA.1, BA.2, and BA.1.1 strains has elevated issues of diminished efficacy of coronavirus illness 2019 (COVID-19) vaccines. This has accelerated the event of antiviral brokers and monoclonal antibodies (mAbs) to broaden the therapeutic panorama of COVID-19.

Study: Characterization and antiviral susceptibility of SARS-CoV-2 Omicron/BA.2. Image Credit NIAID​​​​​​​Research: Characterization and antiviral susceptibility of SARS-CoV-2 Omicron/BA.2. ​​​​​​​Picture Credit score NIAID

In regards to the examine

Within the current examine, researchers evaluated BA.2 pathogenicity and infectivity in hamsters and mice compared to the SARS-CoV-2 D614G WA1/2020 D614G, Beta, and Omicron BA.1 variants.

BA.2 variants similar to HP353, NCD1288, TY40-385, and HP354 have been remoted in VeroE6/TMPRSS2 (transmembrane serine protease 2) cell strains. TY40-385 and NCD1288 isolates have been obtained from Indian vacationers arriving in Japan, whereas HP354 and HP353 isolates have been obtained from Japanese residents.

BALB/c mice have been inoculated intranasally with 105 plaque-forming models (PFU) of BA.1 or BA.2. Subsequently, adjustments of their weight and pulmonary operate have been assessed. Their Rpef and Penh values have been measured by whole-body plethysmography (WBP) to determine pulmonary adjustments. Moreover, the pulmonary and nasal turbinate tissues of the mice have been subjected to histopathological evaluation, in situ hybridization, and immunohistochemistry evaluation and their cytokine and chemokine ranges have been assessed.

Related analyses have been carried out in human angiotensin-converting enzyme 2 (hACE2)-expressing transgenic K18 mice and hamsters for comparative evaluation of the D614G, Beta, BA.1, and BA.2 variants. As well as, micro-computed tomography (micro-CT) evaluation and next-generation sequencing (NGS) have been carried out.

BA.2 neutralization was assessed amongst COVID-19 convalescents and BNT162b2 vaccinees by focus discount neutralization checks (FRNT) and the titers have been in comparison with these of the D614G, Delta, BA.1, and BA.1.1 variants. Additional, FRNT assays utilizing SARS-CoV-2-infected hamster antisera have been carried out to evaluate the antigenic properties of the three Omicron variants. Therapeutic efficacies of Meals and Drug Administration (FDA)-authorized mAbs and antiviral brokers in opposition to BA.1 and BA.2 have been additionally evaluated.


At two days post-infection (dpi), BA.1- and BA.2-infected BALB/c mice didn’t display any adjustments of their weight or pulmonary operate, in distinction to considerably increased Penh and decrease Rpef values amongst Beta-infected mice. The pulmonary BA.2 titers (6.9 log10 PFU/g) have been increased than BA.1 titers (6.4 log10 PFU/g). At 5 dpi, the pulmonary BA.2 titers decreased by 33-fold in comparison with BA.1 at 5 dpi. However, BA.1 and BA.2 titers within the nasal turbinates remained related.

Histopathological evaluation confirmed minimal inflammatory infiltrate in pulmonary alveolar and peri-bronchial/bronchiolar areas amongst BA.1- and BA.2-infected mice. In situ hybridization evaluation revealed the presence of SARS-CoV-2 ribonucleic acid (RNA) within the alveolar and bronchiolar epithelium of BA.1- and BA.2-infected mice. The immunohistochemistry evaluation confirmed an analogous distribution of SARS-CoV-2 antigen and RNA amongst mice contaminated by BA.1 or BA.2. The analyses indicated comparable BA.1 and BA.2 infectivity, albeit decrease than Beta.

Compared to BA.1-infected mice, these contaminated by BA.2 confirmed a considerably better expression of inflammatory chemokines and cytokines, similar to interleukin-1 beta (IL-1β), interferon-gamma (IFN-ꓬ), and macrophage inflammatory protein-1 beta (MIP-1β). Nevertheless, the inflammatory expression was considerably decrease than these of Beta infections, indicative of the low BA.2 replicative functionality.

At three dpi, hACE2-expressing K18 mice confirmed considerably decrease BA.1 and BA.2 titers and RNA within the lungs and nasal turbinates than D614G titers. The BA.2-induced expression of chemokines and cytokines [IL-1β, MIP-1α, and tumor necrosis factor-alpha (TNF-α)] have been increased than these induced by BA.1 however decrease than these by D614G. This means decrease pathogenicity for BA.1 and BA.2 than for D614G.

Syrian hamsters didn’t display any variations in weight or pulmonary operate on inoculation with 103 or 105 PFU doses of SARS-CoV-2 strains. At three dpi and 103 inoculations, the nasal turbinate and pulmonary BA.1 titers have been considerably better than BA.2 titers. Nevertheless, at 105 inoculation doses, the BA.1 and BA.2 pulmonary titers have been related. As well as, no important variations have been detected in BA.1- and BA.2-infected hamsters within the in situ hybridization, histopathological evaluation, and immunohistochemistry evaluation. The findings point out that BA.1 and BA.2 have comparable pathogenicity.

The micro-CT evaluation confirmed pneumonia-like pulmonary pathological adjustments amongst BA.1- and BA.2-infected hamsters with increased CT severity scores amongst these contaminated by BA.2. NGS evaluation confirmed BA.1 predominance within the lungs and nasal turbinates of the hamsters at each inoculation doses.

All K18 transgenic hamsters (together with M51 cell line) inoculated with 103 PFU of D614G died at 5 dpi, whereas most BA.1- and BA.2-infected hamsters survived. Pulmonary BA.2 titers have been decrease by 100-fold and 10,000-fold than the corresponding BA.1 titers and D614G titers, respectively. Nevertheless, all strains confirmed comparable titers within the nasal turbinates.

The FRNT evaluation confirmed that BNT162b2 vaccination led to a extra important discount of BA.1 and BA.1.1 titers in comparison with BA.2 titers. Delta-infected vaccinees confirmed excessive 50% FRNT (FRNT50) values in opposition to Delta however low FRNT50 values in opposition to the three Omicron strains. Omicron-infected vaccinees confirmed FRNT50 values 2.9-fold to three.6-fold decrease in opposition to the Omicron strains than Delta.

Hamster antisera raised in opposition to the Omicron strains confirmed markedly low FRNT50 titers in opposition to the D614G and Delta strains. As well as, 17.4-fold and 11.7-fold decrease neutralization of BA.1.1 and BA.1 and in comparison with BA.2, respectively, have been noticed. This means that BA.2 differs antigenically from the D614G, Delta, BA.1, and BA.1.1 strains.

Amongst mAbs, COV2-2196/COV2-2130, S309, and REGN10987/REGN10933 inhibited pulmonary SARS-CoV-2 replication in BA.2-infected hamsters. Amongst antiviral medicine, all considerably decreased the pulmonary BA.2 titers. As well as, S-217622 decreased BA.2 titers within the nasal turbinates.

General, the examine findings confirmed that BA.2 pathogenicity and infectivity have been similar to BA.1 however decrease than different SARS-CoV-2 variants.

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