June 16, 2025, 10:50 am | Read time: 4 minutes
Cough, sore throat, fever–initially, an infection with the new coronavirus variant NB.1.8.1 appears like a typical respiratory infection. But that’s misleading: The subvariant, also known as “Nimbus,” not only causes sometimes severe symptoms but is also spreading rapidly worldwide. Affected individuals frequently report extremely painful sore throats. FITBOOK editor Julia Freiberger explains the underlying causes of these symptoms and assesses the true danger of the new variant.
“Nimbus,” scientifically known as NB.1.8.1, is a new Omicron subvariant that the WHO reports has been increasingly detected since January. While it already dominates in China, its prevalence is also rising significantly in the U.S. In Germany, initial detections have been made–though many infections are likely to go unnoticed.
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Overview
What is NB.1.8.1 (“Nimbus”)?
The coronavirus variant NB.1.8.1 is a subvariant of the Omicron lineage, tracing back to a recombinant form called XDV.1.5.1, as previously reported by FITBOOK. It has several mutations in the spike protein that could make the virus more contagious. However, early analyses indicate that the new variant has not yet led to more severe illnesses than previous variants. Initial lab and clinical data also support the assumption that current vaccines continue to offer protection. Breakthrough infections may occur in individuals with waning immunity or those who are unvaccinated.1
Why is the variant called “Nimbus”?
The name “Nimbus” was not given by an official health authority but was suggested on social media by Canadian evolutionary biologist T. Ryan Gregory in late May 2025. He had previously named other variants, such as the “FLiRT” strains. Although the term “Nimbus” is unofficial, it is now frequently used by media and experts.
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Typical symptoms of the coronavirus variant
The symptoms caused by NB.1.8.1 largely resemble those of earlier Omicron variants. Commonly reported are fever, fatigue, cough, and sore throat. Notably, some individuals report particularly intense sore throats–sometimes feeling like “razor blades in the throat.” Experts suspect that the virus variant may prefer to multiply in the throat area, potentially intensifying local symptoms.
Other typical symptoms include:
- Dry cough
- Shortness of breath
- Runny or stuffy nose
- Loss of smell or taste
- Head and body aches
- Severe fatigue
Health facilities emphasize, however, that distinctive symptoms of individual virus lines have not yet been scientifically confirmed and are usually only described in isolated cases.2
Spread in the U.S.
In the United States, the share of NB.1.8.1 is increasing significantly. According to the U.S. health agency CDC (Centers for Disease Control and Prevention), the variant accounted for about 37 percent of recorded COVID-19 cases in the two weeks ending June 7–a significant increase from 15 percent two weeks earlier.3 This places it second behind the currently dominant lineage LP.8.1.
The CDC, however, emphasizes that the data’s reliability is limited, as fewer genetic virus analyses are being conducted.
According to official reports, NB.1.8.1 had been identified in at least 14 states by mid-June, including California, New York, Illinois, Hawaii, and Virginia. The WHO also reported that by May 27, the variant had affected 22 countries, with a global share of 10.7 percent.4,5
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What is the situation in Germany?
According to the RKI, the variant NB.1.8.1 was first detected in Germany in late March 2025.6 Since then, only isolated cases have been identified. It is currently not possible to make statements about how strongly or quickly the subvariant is spreading.
Overall, COVID-19 infections in Germany remain at a low level. In the week ending June 8, the share of COVID-19 cases among respiratory illnesses was only one percent, according to the Robert Koch Institute.7 However, the number of unreported cases is likely much higher–partly because very few people are being tested now. The so-called wastewater monitoring provides clues to other unrecorded infections: It measures how many virus residues are present in wastewater at treatment plants. Here, too, a slight increase is evident–but the overall infection situation is still considered low.
How dangerous is NB.1.8.1?
According to current knowledge, NB.1.8.1 does not cause more severe illness than other virus variants. International health authorities report rising case numbers and isolated hospitalizations but see no evidence of increased disease severity. Chinese authorities also report no significant worsening in clinical outcomes despite the variant’s spread.