New COVID-19 Variant NB.1.8.1 Dominates China and Hong Kong, Spreads to Australia and US

The World Health Organization designated NB.1.8.1 as a “variant under monitoring” on 30 May 2025 due to its growing global spread and notable characteristics.

NB.1.8.1 was first detected from samples collected in January 2025. The variant is a sublineage of the Omicron variant, descending from the recombinant XDV lineage where genetic mixing of two or more existing variants creates new strains.

By late April 2025, NB.1.8.1 comprised roughly 10.7% of all submitted sequences globally. This figure jumped from just 2.5% four weeks prior.

The variant now dominates in China and Hong Kong. It has also been detected in sewage samples in California, USA, and is spreading across the US and parts of Europe.

NB.1.8.1 COVID Variant Shows Strong Transmission Capabilities in Australia

Genomic sequencing confirmed NB.1.8.1 is among the circulating strains in Australia and generally increasing. Of cases sequenced up to 6 May across Australia, NB.1.8.1 ranged from less than 10% in South Australia to more than 40% in Victoria.

Wastewater surveillance in Western Australia determined NB.1.8.1 is now the dominant variant in wastewater samples collected in Perth.

Associate Professor Lara Herrero from Griffith University stated the NB.1.8.1 variant might overtake other strains. “The new strain is now the dominant coronavirus strain in China and Hong Kong and, in Australia, we’re seeing it pretty much everywhere,” she said.

Available data suggests case numbers in Australia were ticking upwards in late May 2025. It remains more difficult to track virus occurrence nowadays as fewer people are testing and reporting infections.

NB.1.8.1 carries mutations in the spike protein including T22N, F59S, G184S, A435S, V445H, and T478I. Lab-based research found NB.1.8.1 had the strongest binding affinity to the human ACE2 receptor of several variants tested.

The study showed the neutralising response of antibodies was around 1.5 times lower to NB.1.8.1 compared with another recent variant, LP.8.1.1. This suggests a person infected with NB.1.8.1 may be more likely to pass the virus to someone else compared with earlier variants.

COVID-19 Variant NB.1.8.1 Symptoms and Vaccination Protection Remain Similar

Dr John Swartzberg from the University of California, Berkeley, warned that low COVID-19 case numbers in 2025 may not continue and could change by autumn or winter.

“This variant appears to attach more easily to human cell receptors, which means it has the potential to be more infectious. This is not good news,” Dr Swartzberg said.

The WHO has not observed any evidence that NB.1.8.1 causes more severe disease compared with other variants. Symptoms should align closely with other Omicron subvariants.

Common symptoms include sore throat, fatigue, fever, mild cough, muscle aches and nasal congestion. Gastrointestinal symptoms may also occur in some cases.

Health authorities in Hong Kong expect cases to decline in “a month or two.” Thailand reported 67,484 cases of the virus in just seven days, prompting many to mask up again in China, Thailand, and Singapore.

Current COVID vaccines should still protect against severe disease with this variant, according to the WHO. The most recent booster available in Australia and many other countries targets JN.1, from which NB.1.8.1 is descended.

Experts don’t see a need for travel restrictions or worldwide lockdowns yet. Vaccine jabs are highly recommended, especially for those who are travelling.

Public health responses remain focused on close monitoring, continued genomic sequencing and promoting the uptake of updated COVID boosters.