July 2, 2025, 2:03 pm | Read time: 5 minutes
Sharp throat pain that feels like swallowing razor blades—this symptom is particularly noticeable in infections with the new coronavirus variant NB.1.8.1. The subvariant, also known as “Nimbus,” is spreading rapidly worldwide and is often initially mistaken for a common respiratory infection. But appearances can be deceiving: FITBOOK editor Julia Freiberger explains what NB.1.8.1 is all about and how dangerous the new variant really is.
“Nimbus,” officially called NB.1.8.1, is a new Omicron subvariant that, according to the WHO, has been spreading worldwide since January. It already dominates in China, is gaining ground in the U.S., and has now been detected in Germany. Particularly notable: the sometimes extremely severe sore throat. Below, FITBOOK discusses the new coronavirus variant.
Overview
Notable Symptom of NB.1.8.1: Razor Blade Feeling in the Throat
A particularly noticeable sign of infections with NB.1.8.1 is the intense sore throat that many affected individuals report. The pain is described not as ordinary but as unusually strong and sharp—like “razor blades in the throat.” Especially when swallowing, patients feel a sharp pain deep in the throat, which is sometimes perceived as excruciating. Chinese doctors report patients describing these symptoms as so extreme that it feels like swallowing razor blades. This drastic description has earned the variant the nickname “Razor Throat” or “Razor Blade Throat.”1 According to experts, the viruses may multiply more in the throat area, which could explain the increased occurrence of sore throats.
The international expert initiative “World Health Network” refers to this symptom combination of severe sore throat and massive fatigue as “razor-blade throat fatigue.” Despite the strain, the variant is not considered fundamentally more dangerous. Fever, runny nose, vomiting, and diarrhea can also occur—a symptomatology that goes beyond what was previously known from earlier variants.2
Other Symptoms of the Coronavirus Variant
In addition to sore throats, classic symptoms such as dry cough, shortness of breath, a stuffy or runny nose, loss of smell or taste, and headaches and body aches are also mentioned. Many infected individuals also report extreme fatigue. Health facilities, however, point out that distinctive symptoms of individual virus variants have so far mostly been described only sporadically and are not yet scientifically proven.3
What is NB.1.8.1 (“Nimbus”)?
The coronavirus variant NB.1.8.1 is a subvariant of the Omicron line and traces back to a recombinant form called XDV.1.5.1, as FITBOOK previously reported. It has several mutations in the spike protein that could make the virus more contagious. Early analyses, however, show that the new variant has not yet led to more serious illnesses than predecessor variants. Initial laboratory and clinical data also support the assumption that current vaccines continue to provide protection. Breakthrough infections can occur in people with waning immunity or those who are unvaccinated.4
Why is the Coronavirus Variant Called “Nimbus”?
The name “Nimbus” does not come from an official health authority but was proposed 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 the media and experts.
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 was responsible for about 37 percent of recorded coronavirus cases in the two weeks ending June 7–a significant increase compared to 15 percent two weeks earlier.5 This places it second behind the currently dominant line LP.8.1.
However, the CDC emphasizes that the data’s reliability is limited, as fewer genetic virus analyses are being conducted.
According to official reports, the coronavirus variant 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, 22 countries were affected by the variant, with a global share of 10.7 percent.6,7
What is the Situation in Germany?
According to the RKI, the variant NB.1.8.1 was first detected in Germany at the end of March 2025.8 Since then, only isolated cases have been identified. However, current data show that its share of the examined SARS-CoV-2 samples rose to about 20 percent in May, up from around six percent in April.9 It is currently not possible to make statements about how strongly or quickly the subvariant is spreading.
Overall, coronavirus infections in Germany remain at a low level. In the week ending June 8, the share of COVID-19 cases among respiratory diseases was only one percent, according to the Robert Koch Institute.10 However, the number of unreported cases is likely significantly higher—partly because very few people are being tested now. The so-called wastewater monitoring provides clues to other undetected infections: It measures how many virus residues are present in wastewater at treatment plants. Here, too, there is a slight increase, but the overall infection situation is still considered low.
WHO Assessment
The World Health Organization (WHO) currently lists NB.1.8.1 as a “variant under monitoring” (VUM)—the lowest of three risk categories. Although the subtype has genetic changes that could promote faster spread, there are no signs of more severe disease courses or reduced vaccine effectiveness so far. A classification as a “variant of interest” (VOI) or even as a “variant of concern” (VOC) would only occur if noticeable impacts on public health were observed. Currently, the WHO sees no reason for this.11
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How Dangerous is NB.1.8.1?
According to current knowledge, NB.1.8.1 does not cause more severe disease courses than other virus variants. International health authorities report rising case numbers and isolated hospitalizations but have not yet seen any evidence of increased disease severity. Chinese authorities also report no significant worsening in clinical outcomes despite the variant’s spread.