Rapidly Emerging Covid Variant: Insights Revealed on NB.1.8.1
A new COVID-19 variant, NB.1.8.1, also known as "Nimbus," has surfaced and could play a significant role in Australia's upcoming winter respiratory season. This recombinant or hybrid virus, descended from the XDV lineage, has been making waves globally due to its increased infectivity and potential implications for immunity and vaccine effectiveness.
**Key Characteristics**
NB.1.8.1 is a unique strain resulting from the genetic recombination of multiple Omicron subvariants. It carries seven new mutations in its spike protein, as well as approximately 20 additional mutations elsewhere in its genome. These spike protein mutations enhance the virus's ability to strongly bind the ACE2 receptor on human cells, improving cell entry and infectivity.
**Transmission Rates**
Laboratory studies show NB.1.8.1 binds more strongly than most other variants to the ACE2 receptor and exhibits high infectivity in lab-grown cells. Its infectivity is approximately 2.5 times higher than LP.8.1, which was previously the most prevalent variant globally. Epidemiological data indicate NB.1.8.1 has rapidly increased in prevalence worldwide, from 2.5% of sequenced cases in late March 2025 to 10.7% by late April 2025, and has been detected in at least 22 countries.
**Immunity and Vaccine Effectiveness**
NB.1.8.1 shows marginal immune evasion compared to other circulating variants, but there is no evidence it significantly escapes immunity from prior infection or vaccination. Current COVID-19 vaccines are expected to continue providing protection against severe illness caused by NB.1.8.1. The variant’s increased transmissibility is thought to be more due to biological infectivity than enhanced immune escape.
**Symptoms and Severity**
Symptoms of NB.1.8.1 infections are similar to those of recent Omicron variants, including fatigue, fever, sore throat, congestion, and occasionally gastrointestinal symptoms. There is no evidence that NB.1.8.1 causes more severe disease compared to previous strains or other Omicron subvariants in circulation. The World Health Organization (WHO) has classified NB.1.8.1 as a "variant under monitoring" and assesses the public health risk as low as of late May 2025.
**Summary**
In essence, NB.1.8.1 spreads more efficiently due to enhanced infectivity but does not appear to cause more severe illness or significantly evade existing immunity or vaccines. Current health authorities recommend monitoring but do not consider it a high-risk variant at this time.
As we approach winter and with a new variant on the scene, it may be a good time to consider another COVID-19 booster if you're eligible, particularly for medically vulnerable individuals. Public health responses remain focused on close monitoring, continued genomic sequencing, and promoting the uptake of updated COVID-19 boosters. The WHO has not yet observed any evidence that NB.1.8.1 causes more severe disease compared to other variants.
- Gizmodo reports on the new COVID-19 variant, NB.1.8.1, also known as "Nimbus," which could significantly impact Australia's upcoming winter respiratory season.
- This recombinant virus, a unique strain resulting from the genetic recombination of multiple Omicron subvariants, carries seven new mutations in its spike protein and approximately 20 additional mutations elsewhere in its genome.
- Despite showing marginal immune evasion compared to other circulating variants, the increased transmissibility of NB.1.8.1 is thought to be more due to biological infectivity than enhanced immune escape, and current health authorities recommend monitoring but do not consider it a high-risk variant at this time.
- To stay protected during the upcoming winter season and against this new variant, it may be beneficial for eligible individuals, especially those with medical conditions, to consider getting another COVID-19 booster. Public health responses remain focused on close monitoring, continued genomic sequencing, and promoting the uptake of updated COVID-19 boosters.
