Australia is witnessing a rise in COVID-19 cases linked to a newly identified variant, NB.1.8.1. This sublineage of Omicron has attracted global attention due to its increasing spread and distinct genetic characteristics.
As the colder months begin, public health officials are closely monitoring the situation to understand the implications of NB.1.8.1 for the coming respiratory season. Its emergence raises important questions about transmission, immunity, and vaccine effectiveness.
NB.1.8.1’s Spread and Prevalence in Australia and Beyond
According to the World Health Organization (WHO), the variant was first detected in January 2025 and is now designated as a “variant under monitoring” because of its rising presence worldwide. In Australia, genomic sequencing reveals a growing share of cases attributed to NB.1.8.1, with notable regional differences.
For example, less than 10% of sequenced cases in South Australia are linked to this variant, whereas in Victoria, it represents more than 40% of sequenced infections.
Wastewater surveillance in Perth, Western Australia, confirms NB.1.8.1 as the dominant strain in recent samples, indicating widespread community transmission. Internationally, the variant has seen rapid growth in Asia, particularly in Hong Kong and China, where it became the dominant strain by late April 2025.
The variant descends from the recombinant XDV lineage, which combines genetic material from multiple previous strains. This recombination may contribute to its distinctive properties and ability to spread efficiently.
Scientific Insights Into NB.1.8.1’s Characteristics and Vaccine Implications
The new variant carries multiple mutations in the spike protein—the key viral component that binds to human cells via ACE2 receptors. Early research, including a recent preprint study, suggests this strain exhibits a stronger binding affinity to ACE2 than several other variants tested. This feature could enhance the virus’s capacity to infect cells.
The same study observed that antibodies from vaccinated individuals or those previously infected showed approximately 1.5 times lower neutralising activity against NB.1.8.1 compared to other recent variants.
This reduced neutralisation might partly explain the variant’s increased transmissibility, though there is currently no evidence indicating more severe illness caused by NB.1.8.1.
Vaccination remains a critical defence. The latest booster available in Australia targets the JN.1 lineage, from which NB.1.8.1 descends, and is expected to maintain good protection against severe outcomes. Health authorities continue to recommend booster uptake, particularly for vulnerable populations, as the virus circulates during the winter months.
