In this latest video from Medcram, Dr. Seheult discusses the new COVID-19 subvariant known as NB.1.8.1, nicknamed “Nimbus”. A recent report from The Conversation sheds light on the evolving nature of SARS-CoV-2 and the continuing adaptations of the Omicron lineage. NB.1.8.1 is currently gaining traction in parts of Australia and Asia, especially as the Southern Hemisphere heads into winter.
What is NB.1.8.1?
NB.1.8.1 is a descendant of the Omicron variant, and early genomic sequencing reveals that it carries mutations in the spike protein that help it evade immune defenses more effectively than its predecessors. While it does not appear to increase the severity of illness, it does show signs of increased transmissibility, possibly due to tighter binding to the ACE2 receptor, the entry point for the virus into human cells. Preliminary studies, although not yet peer-reviewed, suggest this subvariant also exhibits modest immune escape, particularly affecting antibody neutralization.
The World Health Organization has designated NB.1.8.1 as a “variant under monitoring.” Wastewater surveillance—considered a more objective measure compared to individual testing—has shown NB.1.8.1 becoming dominant in Perth and Western Australia. Genomic data indicates the variant has risen from 2.5% to 10.7% of global sequenced cases as of April 2025, with Hong Kong and China seeing the highest prevalence. In the U.S., confirmed cases remain low (just 20 reported by late May), but the pattern of spread suggests it could rise, particularly given its potential for rapid transmission.
Symptoms of NB.1.8.1
Symptoms associated with NB.1.8.1 are similar to other Omicron subvariants: sore throat, fever, mild cough, fatigue, muscle aches, and nasal congestion, with some reports of gastrointestinal symptoms. Importantly, no evidence suggests an increase in disease severity, and current vaccines are still expected to protect against severe disease, even if neutralizing antibodies are slightly less effective.
SARS-CoV-2 continues to have a strong ability to evade the immune system. A key player here is the MAC1 gene, a viral component that enables SARS-CoV-2 to block the body’s interferon response—one of our innate immune system’s most powerful defenses against viruses. Interferons work by activating a cascade of genes that create an antiviral environment. Many viruses, including SARS-CoV-2, have evolved mechanisms to shut down this pathway. In the case of SARS-CoV-2, MAC1 allows it to bypass interferon signaling and establish infection.
Studies show that when the virus is engineered without a functioning MAC1 gene, interferon responses surge, suggesting that targeting this gene could make the virus far less effective. One promising therapeutic approach involves the use of pegylated interferon lambda, which, in a large randomized clinical trial, reduced COVID-related hospitalizations or emergency visits by approximately 50%, regardless of vaccination status. This reinforces the idea that bolstering interferon response could be a key strategy in combating not only current but future variants.
How does fever help?
Moreover, it’s been observed that fever itself—an increase in body temperature even by 1°C—can naturally enhance interferon activity. This raises important questions about the common practice of suppressing fevers with medication, as fever may be the body’s way of enhancing its antiviral response through upregulated interferon production. Lab studies support this, showing that macrophage and immune signaling pathways become more active at higher (but still safe) body temperatures, further confirming the potential protective role of fever.
Meanwhile, in a related development, the U.S. government recently canceled over $700 million in funding to Moderna for development of an mRNA-based vaccine for H5N1 (bird flu). This decision was made after an internal review concluded the project did not meet safety or scientific standards. While existing H5N1 vaccines do exist, they are not based on mRNA technology and may be ineffective against newer strains. Moderna has stated that it intends to explore alternative paths for developing the vaccine, but this move may slow progress on a potentially rapid-response tool if H5N1 were to begin spreading among humans.
Ultimately, the evolution of NB.1.8.1, the role of interferon in viral defense, and the regulatory setbacks in pandemic preparedness all underscore a key theme: public health vigilance remains essential. While the world has moved beyond the emergency phase of the COVID-19 pandemic, new variants will continue to arise, and our response—whether through updated vaccines, enhanced surveillance, or boosting innate immunity—must remain agile and scientifically grounded.
LINKS / REFERENCES:
A new COVID variant is sweeping through China. Here’s what to know about NB.1.8.1 (USA Today) | https://www.usatoday.com/story/news/h…