A newly designated sublineage of Omicron, named NB.1.8.1, has rapidly established itself as the dominant COVID-19 variant in parts of Asia and is now “pretty much everywhere” in Australia, according to leading virologists. First detected in January 2025, NB.1.8.1 carries mutations in the spike protein that appear to enhance its transmissibility and ability to evade immune defenses. In early May, the World Health Organization classified NB.1.8.1 as a Variant Under Monitoring, underscoring the need for heightened surveillance and vaccination efforts as the southern hemisphere heads into winter.
Global Spread and WHO Designation
NB.1.8.1 emerged from the JN.1 lineage of Omicron, which itself supplanted earlier variants such as BA.5 and XBB.1.5. By March, public health laboratories in China and Hong Kong reported NB.1.8.1 had quickly outcompeted other strains to account for the majority of new cases. Its rise coincided with increased respiratory illness across the region, prompting governments to reintroduce mask mandates in high-risk settings and accelerate booster campaigns.
On 5 May, the WHO formally added NB.1.8.1 to its list of Variants Under Monitoring, a category reserved for strains that exhibit worrisome genetic changes or for which preliminary data suggest altered transmissibility, immune escape, or clinical severity. Unlike a “Variant of Interest” or “Variant of Concern,” this classification does not imply definitive evidence of increased severity, but signals that additional research and data collection are needed.
Arrival and Detection in Australia
Associate Professor Lara Herrero of Griffith University, a noted virologist, confirmed that sequences of NB.1.8.1 have been identified in all major Australian jurisdictions. “We’re seeing it pretty much everywhere,” Herrero said. “There is a prediction that this might start taking over other strains, but it’s early days, so we’ll just wait and see.” Despite COVID-19 reporting no longer being mandatory in Australia, hospital emergency departments have observed a resurgence in COVID-related admissions since May.
Genomic surveillance programs run by the Doherty Institute and various state public health labs have tracked the proportion of COVID-19 cases due to NB.1.8.1 rising from under 5 percent in April to an estimated 30 percent by mid-May. The rapid increase aligns with the variant’s higher basic reproduction number (R₀), which preliminary modelling places at 1.4 to 1.6, compared with 1.1 to 1.3 for the previous dominant sublineages.
Clinical and Virological Characteristics
Unlike some earlier VOCs (Variants of Concern), NB.1.8.1 does not appear to cause more severe disease. Infectious disease physician Paul Griffin noted: “There’s no evidence that symptoms are any worse—patients present with fevers, cough, runny nose, headache, body aches, and occasionally gastrointestinal upset, much as we’ve seen throughout the pandemic.” Griffin cautioned, however, that the sheer volume of infections could overwhelm healthcare resources, particularly if concurrent influenza and RSV waves peak.
Laboratory assays indicate that NB.1.8.1 harbors several key spike mutations—namely L452R, F456L, and R346T—which studies suggest bolster binding affinity to the ACE2 receptor and reduce neutralisation by antibodies elicited by previous infection or vaccination. Neutralisation tests using post-booster sera demonstrate a 3- to 5-fold reduction in antibody potency against NB.1.8.1 compared with the reference JN.1 strain, but still retain sufficient activity to prevent severe outcomes when combined with T-cell–mediated immunity.
Vaccines and Boosters: Maintaining the Defense
Public health authorities are urging Australians to receive a COVID-19 booster—particularly the recently updated JN.1-targeted formulation—if they have not done so in the past twelve months. Health Minister Mark Butler emphasised the convenience of obtaining free boosters at local pharmacies and GP clinics, noting that all Australians aged 5 and above remain eligible.
Despite broad eligibility, uptake in the first half of 2025 has been alarmingly low: only 6.6 percent of adults have received any COVID booster since January. In contrast, annual influenza vaccination rates have hovered near 60 percent in recent years, suggesting that vaccine hesitancy and complacency toward COVID persists.
Dr. Herrero stressed the importance of dual protection: “The flu is nasty this season, too, so I’d very strongly recommend everyone get their yearly flu vaccine and the JN.1 COVID booster—it’s the best way you’re going to be protected if you haven’t had COVID in the last six months.” Similarly, Dr. Michael Bonning of the Australian Medical Association (NSW) echoed that “individual variants are probably less important than overall societal factors such as whether people are keeping up to date with boosters.”
Winter Respiratory Season: A Perfect Storm
Australia is entering what experts predict will be a particularly challenging winter, as evidenced by northern hemisphere trends. In New South Wales, recent data show a 29.2 percent rise in COVID-19 notifications, a 25.9 percent increase in influenza cases, and a 9.7 percent uptick in RSV over the past week alone. Emergency departments report crowded wards, and general practices are experiencing surges in respiratory illness consultations.
With NB.1.8.1’s enhanced transmissibility, co-circulation of seasonal pathogens, and waning immunity among the population, health systems face the risk of dual epidemics. Dr. Bonning warned: “We are expecting a spike in cases over the coming weeks, with an expectation of a particularly difficult winter respiratory season.” He urged continued mask usage in high-risk settings and staying home when symptomatic to curb nosocomial and community spread.
Public Health Measures and Self-Protection
Although most legal restrictions have been lifted, health experts recommend a layered approach to protection:
- Vaccination and Boosters: Ensure primary series and booster doses are up to date for both COVID-19 and influenza.
- Masks: Wear well-fitting masks in crowded, indoor, or poorly ventilated spaces, especially during peak respiratory season.
- Hygiene: Frequent handwashing, use of alcohol-based sanitiser, and routine cleaning of high-touch surfaces.
- Testing and Isolation: Perform rapid antigen tests when symptomatic, and isolate for at least five days or until symptom resolution, whichever is longer.
- Ventilation: Enhance indoor airflow through open windows, air purifiers, or HVAC system upgrades.
Associate Professor Herrero summarised: “We’re probably all getting tired of these messages, but I’d just say to people: be vigilant before you get sick. Wash your hands, don’t go out in public if you’re sick and spread it to everyone, get your vaccines if you want them. If you’ve got a cough or cold, I’d wear a mask because you don’t want to share that with other people.”
Addressing Vaccine Hesitancy and Equity
Public surveys indicate that many Australians underestimate the ongoing risk posed by COVID-19. Physician Paul Griffin noted that 500 people have already died this year from COVID-related illness, a stark reminder that the virus remains a significant public health threat.
To overcome vaccine fatigue, health departments are launching targeted communications campaigns—leveraging social media influencers, community ambassadors, and primary care networks—to highlight personal stories of severe COVID cases and the benefits of booster protection. Additionally, mobile vaccination clinics are being deployed in underserved and rural areas to enhance equity of access.
READ MORE: Early Measles Vaccination Gains Urgency Amid Global Outbreak
Employers and educational institutions are encouraged to facilitate on-site vaccination drives and provide paid leave for employees and students recovering from respiratory illnesses. By integrating COVID boosters into routine preventive health checks—such as annual flu clinics—authorities hope to normalise the practice and raise booster coverage toward the 70 percent threshold needed to blunt the next wave.
Surveillance and Research: Staying Ahead of the Curve
Genomic surveillance remains pivotal in tracking NB.1.8.1’s trajectory and detecting any emergent sublineages. The Australian Centre for Disease Preparedness is collaborating with international partners to sequence a representative sample of positive cases weekly. Early findings will inform vaccine strain updates and guide non-pharmaceutical intervention policies.
Meanwhile, clinical trials are underway to evaluate next-generation pan-beta-coronavirus vaccines and mucosal immunisation strategies aimed at blocking infection at the site of viral entry. Monoclonal antibody developers are also assessing broadly neutralising candidates against NB.1.8.1’s spike mutations, offering potential prophylactic options for immunocompromised individuals.
Outlook: Vigilance and Adaptation
More than five years since the declaration of the COVID-19 pandemic, the emergence of NB.1.8.1 serves as a reminder that SARS-CoV-2 will continue to evolve. While current vaccines retain protection against severe disease, the cycle of waning immunity and variant-driven waves underscores the need for sustainable public health strategies.
Through booster campaigns, masking when warranted, and ongoing surveillance, Australia aims to navigate the coming months with resilience. As Dr. Herrero concluded, “As the virus mutates, it gets a little sneakier and better at evading our immune response and antibodies. Our best defense remains vaccination, vigilance, and solidarity in protecting the most vulnerable.”
