Tejal Somvanshi
A new COVID-19 subvariant called NB.1.8.1 is driving up infections across Australia, particularly in Western Australia where it has become the dominant strain in Perth’s wastewater. As winter sets in, health officials are closely monitoring this latest development in the ongoing pandemic.
The World Health Organization (WHO) designated NB.1.8.1 as a “variant under monitoring” on May 23, 2025, due to its increasing global spread. First detected in January 2025, this Omicron sublineage descended from the recombinant XDV lineage.
Rising Numbers in Western Australia
COVID-19 hospitalizations in Western Australia have increased to an average of 38 patients per day, up from 31 in the previous week. This coincides with higher concentrations of the virus in Perth wastewater.
The variant’s global presence has grown rapidly, jumping from just 2.5% of sequenced samples four weeks ago to 10.7% by late April. Beyond Australia, NB.1.8.1 has spread significantly across Asia, particularly in China and Hong Kong, where cases have reached their highest levels in 12 months.
What Makes This Variant Different?
Research suggests NB.1.8.1 may be more efficient at infecting cells than earlier strains. The variant carries specific mutations in its spike protein (including T22N, F59S, G184S, A435S, V445H, and T478I) that appear to enhance its ability to bind to human ACE2 receptors – the entry point for the virus into our cells.
A recent study found that antibodies from vaccinated or previously infected people showed around 1.5 times lower neutralizing response against NB.1.8.1 compared to another recent variant. This suggests people infected with NB.1.8.1 might be more likely to pass the virus to others.
Same Symptoms, Higher Transmission
Despite its increased transmissibility, the WHO has not observed evidence that NB.1.8.1 causes more severe disease than other circulating variants.
Symptoms remain consistent with previous Omicron subvariants:
- Sore throat
- Fatigue
- Fever
- Mild cough
- Muscle aches
- Nasal congestion
- Headache
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Some patients may also experience gastrointestinal symptoms. Loss of taste or smell, which was more prominent in earlier COVID-19 waves, is less frequently reported with this variant.
Vaccine Protection Remains
Health experts emphasize that current COVID-19 vaccines should still provide protection against severe disease from NB.1.8.1. The most recent boosters available in Australia target JN.1, from which NB.1.8.1 is descended, suggesting they should offer good protection.
“Even if neutralizing antibody levels are modestly reduced against NB.1.8.1, COVID-19 vaccines should still protect against severe disease with this variant,” the WHO noted.
Broader Respiratory Concerns
As Australia enters winter, COVID-19 isn’t the only respiratory illness of concern. Influenza activity is also increasing, with notifications now above the seasonal threshold, though health officials note this doesn’t yet indicate the start of flu season.
More than a quarter of this year’s flu cases in Western Australia have been in children under 15. While influenza notifications and hospitalizations are higher than the previous five-year average, deaths remain lower.
The Western Australian government is offering state-funded free flu vaccinations for all residents aged 5 to 64 until June 30, including international visitors and those without Medicare cards. Free RSV immunization is also available for infants and pregnant women.
Expert Advice
Health officials continue to recommend basic precautions:
- Stay up-to-date with vaccinations
- Practice good hand hygiene
- Consider masking in crowded spaces
- Stay home when sick
- Seek medical advice if symptoms worsen
With the rise of NB.1.8.1 and the approaching winter season, health authorities stress vigilance without panic. For most people, COVID-19 continues to cause mild to moderate illness, but those who are medically vulnerable should consider additional precautions, including timely boosters.
