2025-05-28T14:40:30Z

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As winter approaches in Australia, COVID-19 is once again making headlines with the emergence of a new variant known as NB.1.8.1. This variant has recently been designated as a “variant under monitoring” by the World Health Organization (WHO) due to its increasing prevalence and unique characteristics that may differentiate it from earlier strains.

So, what exactly do you need to know about this new variant?

The Current COVID Situation

Five years after COVID-19 was declared a pandemic, Australia continues to experience recurring waves of infections. The current landscape of COVID-19 has become more complex to navigate, as fewer individuals are engaging in testing and reporting their infections. Nevertheless, available data indicates that by late May 2025, COVID case numbers in Australia were on the rise once again. Genomic sequencing has confirmed that NB.1.8.1 is among the strains circulating within the country, with its prevalence steadily increasing. According to reports up to May 6, NB.1.8.1 accounted for less than 10% of COVID cases in South Australia but surged to over 40% in Victoria. Moreover, wastewater surveillance in Western Australia revealed that NB.1.8.1 is now the predominant variant found in samples collected from Perth.

On an international scale, the spread of NB.1.8.1 is also noteworthy. By the end of April 2025, this variant made up approximately 10.7% of all sequenced COVID samples globally, a sharp increase from just 2.5% four weeks earlier. Despite the absolute numbers of sequenced cases being relatively low, the consistent upward trend has prompted public health authorities worldwide to intensify their monitoring efforts. Notably, NB.1.8.1 has gained traction in Asia and emerged as the dominant variant in regions such as Hong Kong and China by the end of April.

Origins of NB.1.8.1

According to the WHO, NB.1.8.1 was first identified in samples collected in January 2025. It belongs to a sublineage of the Omicron variant, specifically descending from the recombinant XDV lineage. The term “recombinant” refers to new variants that arise from the genetic mixing of two or more existing strains, which can potentially lead to significant changes in the virus’s behavior and characteristics.

Research Insights

As with its predecessors, NB.1.8.1 carries a series of mutations in its spike protein, the component of the virus that enables it to infect human cells via ACE2 receptors. These mutations include T22N, F59S, G184S, A435S, V445H, and T478I. Given that it is still early in the emergence of this variant, comprehensive data on the implications of these mutations remains limited. However, preliminary findings from a recent preprint study (a study not yet peer-reviewed) shed light on the variant’s potential for increased transmissibility. Lab-based models indicated that NB.1.8.1 exhibited the strongest binding affinity to the ACE2 receptor among several variants tested, suggesting that it may have a greater capacity to infect cells than earlier strains. Additionally, the study examined how effectively antibodies from vaccinated or previously infected individuals neutralized the variant, revealing that the neutralizing response was approximately 1.5 times lower for NB.1.8.1 compared to another recently identified variant, LP.8.1.1. This finding raises concerns that an individual infected with NB.1.8.1 could potentially transmit the virus more easily than with earlier variants.

Symptoms Associated with NB.1.8.1

Current evidence suggests that NB.1.8.1 may have a propensity for easier transmission and could partially evade immunity acquired from prior infections or vaccinations. These factors may help explain its rapid increase in sequencing data. Importantly, however, the WHO has not yet found any evidence indicating that it causes more severe disease compared to other variants. Symptoms of NB.1.8.1 are anticipated to align closely with those seen in other Omicron subvariants, including sore throat, fatigue, fever, mild cough, muscle aches, and nasal congestion. In some cases, gastrointestinal symptoms may also be present.

Vaccination Outlook

Given the potential impact of this variant, especially during Australia’s winter respiratory season, public health strategies remain focused on vigilant monitoring, ongoing genomic sequencing, and encouraging the uptake of updated COVID-19 vaccine boosters. While neutralizing antibody levels may show modest reductions against NB.1.8.1, the WHO asserts that existing COVID-19 vaccines should still offer protection against severe disease caused by this variant. The most recent booster available in Australia, as well as in several other countries, targets JN.1, the ancestor variant of NB.1.8.1, suggesting that it should continue to provide adequate protection.

As winter sets in and with the introduction of this new variant, it may be prudent for eligible individuals to consider receiving another COVID-19 booster shot. For those who are particularly vulnerable due to medical conditions, COVID-19 can still pose serious health risks.

This article is authored by Lara Herrero, an Associate Professor and Research Leader in Virology and Infectious Disease at Griffith University, and is republished from The Conversation under a Creative Commons license. For further insights, readers can refer to the original article.