Emergent Omicron BR.2.1 sublineage of SARS-CoV-2 in New South Wales, Australia: a subvariant with high fitness but without increased disease severity

Int J Infect Dis. 2023 May:130:38-41. doi: 10.1016/j.ijid.2023.02.019. Epub 2023 Feb 25.


Objectives: To describe the epidemiology and impact of Omicron BR.2.1, an emergent SARS-CoV-2 Omicron BA.2.75 sublineage displaying high fitness compared to other cocirculating subvariants in New South Wales, Australia.

Methods: From September 01 to November 26, 2022, 4971 SARS-CoV-2 consensus genomes from unique patients were generated, and correlated with international travel and reinfection history, and admission to the intensive care unit.

Results: BR.2.1 became the predominant variant by late November, and was responsible for a significantly higher proportion of community-acquired cases during the study period (55.1% vs 38.4%, P < 0.001). Reinfections (defined as occurring between 6 and 24 weeks after a prior diagnosis of COVID-19) were significantly higher among BR.2.1 compared to non-BR.2.1 infected persons (17.0% vs 6.0%, P < 0.001). BR.2.1 cases were also significantly younger compared to non-BR.2.1 (median age 48 years (interquartile range [IQR] 32) vs 53 years (IQR 32), P = 0.004). The proportion of patients admitted to the intensive care unit with BR.2.1 was not significantly higher than other subvariants (2.3% vs 2.0%, P = 0.717).

Conclusion: Having emerged locally within New South Wales, BR.2.1 caused a significant number of SARS-CoV-2 reinfections, but with disease severity comparable with other currently circulating lineages. Given its rapid rise in prevalence, BR.2.1 has the potential to become established internationally.

Keywords: COVID-19; Genomic surveillance; Omicron; SARS-CoV-2; Variants of concern.

MeSH terms

  • Adult
  • Australia
  • COVID-19* / diagnosis
  • COVID-19* / epidemiology
  • Humans
  • New South Wales / epidemiology
  • Patient Acuity
  • Reinfection
  • SARS-CoV-2*


  • carboxymethyl-dextran-A2-gadolinium-DOTA