A new COVID-19 strain is gaining attention, not just for its spread, but for a distinctive symptom that’s earned it a grim nickname. Officially known as NB.1.8.1 and nicknamed “Nimbus,” this variant may be linked to what some describe as a “razor blade throat” – an intensely painful sore throat.
While severe sore throats have been associated with various COVID-19 variants in the past, the “razor blade” description has become notably prominent alongside the spread of NB.1.8.1. Reports of this specific, painful symptom have emerged from doctors and media outlets in the United Kingdom, India, and elsewhere, including anecdotal accounts shared on social media platforms like Reddit.
But what else should you know about Nimbus, its potential risks, and how it fits into the broader picture of the pandemic?
What is the NB.1.8.1 “Nimbus” Variant?
The NB.1.8.1 variant was first detected in China in January. Health experts characterize it as a “slightly upgraded version” of the previously dominant LP.8.1 strain. According to CDC Nowcast estimates for the two-week period ending June 7, NB.1.8.1 accounted for a significant 37% of cases in the U.S., making it the second most common variant nationally, closely following LP.8.1 (38%). Globally, the variant’s presence increased substantially, accounting for 10.7% of sequenced samples in April, up from just 2.5% the previous month, according to data reported by the World Health Organization (WHO).
Some experts, like professor of microbiology and immunology Subhash Verma, suggest that NB.1.8.1 may be more transmissible and potentially better at evading antibodies from prior infection or vaccination compared to LP.8.1. Due to this potential, Verma believes the variant warrants careful monitoring.
Symptoms to Watch For
While the “razor blade throat” symptom is the most talked-about characteristic linked to Nimbus, the CDC has not outlined specific symptoms unique to this variant. Experts generally agree that the symptoms associated with NB.1.8.1 appear similar to those of earlier COVID-19 strains.
Common COVID-19 symptoms, according to the CDC, include:
Fever or chills
Cough
Shortness of breath or difficulty breathing
Sore throat (though potentially severe with Nimbus)
Congestion or runny nose
New loss of taste or smell
Fatigue
Muscle or body aches
Headache
Nausea or vomiting
The CDC also advises seeking immediate medical care for severe symptoms such as trouble breathing, persistent chest pain or pressure, new confusion, inability to wake or stay awake, and pale, gray, or blue skin, lips, or nail beds (depending on skin tone).
Spread and Risk Assessment
The WHO reported in late May that NB.1.8.1 appeared to be driving a recent rise in COVID-19 cases, primarily concentrated in the eastern Mediterranean, Southeast Asia, and western Pacific regions. The variant has also been detected in the United States via airport screening of travelers arriving from these areas, with cases identified in California, Washington state, Virginia, and New York.
California, for example, has seen an increase in coronavirus levels reflected in wastewater surveillance and a rising positive test rate (up to 2.8% state-wide from a March low of 1.1%). NB.1.8.1 was projected to make up a dominant 55% of circulating virus in California as of May.
Despite the increase in cases and the notable sore throat symptom, health experts and the World Health Organization currently assess the overall public health risk posed by the Nimbus variant as low at the global level. While some western Pacific countries have reported increases in both cases and hospitalizations, there is currently no evidence to suggest that the disease caused by NB.1.8.1 is more severe compared to infections from other variants.
The WHO has designated Nimbus as a “variant under monitoring” rather than a variant of concern, reflecting the current assessment that it does not pose a substantially increased risk to public health based on available data.
Protection and Recent Policy Shifts
Fortunately, the WHO expects currently approved COVID-19 vaccines to remain effective against the NB.1.8.1 variant, particularly in preventing symptomatic and severe disease. A CDC recommendation dated January 7, 2025, advises everyone over six months old to receive the 2024-2025 COVID-19 vaccine, with particular emphasis on individuals who have never been vaccinated, those age 65 and older, the immunocompromised, residents of long-term care facilities, pregnant or breastfeeding individuals, those trying to conceive, and those wishing to avoid long COVID.
However, recent developments in U.S. federal health policy have introduced complexity regarding vaccine guidance and access. In May, the Department of Health and Human Services (HHS) under Secretary Robert F. Kennedy Jr. announced changes to the CDC’s official recommendations. Rather than recommending COVID vaccines for all individuals age 6 months and up, the guidance shifted to offering “no guidance” for healthy pregnant women and suggesting parents of healthy children consult a healthcare provider. Additionally, the Food and Drug Administration (FDA) indicated plans to require new clinical trials for the approval of annual COVID-19 boosters for healthy individuals under 65, which could potentially result in some individuals needing to pay out-of-pocket for the vaccine. (Note: Updated/annual vaccines differ from “booster shots,” which are additional doses of the same vaccine; updated vaccines target newer variants like NB.1.8.1).
These federal actions, including the recent dismissal of members of the Advisory Committee on Immunization Practices (ACIP) which advises the CDC on vaccine policy, have drawn strong objections from numerous medical professional organizations, health experts, and state/local health officials. Critics argue these moves weaken the U.S. vaccine program, risk access and insurance coverage, propagate misinformation (particularly regarding pregnant women, who face higher risks from COVID), and erode trust in public health recommendations. Governors and state health departments in states like California have stated they will maintain current, broader recommendations for vaccination based on scientific evidence, despite changes at the federal level.
For those without health insurance, free COVID-19 testing continues to be available nationwide through the federal Increasing Community Access to Testing, Treatment and Response (ICATT) program.
In summary, while the NB.1.8.1 “Nimbus” variant is spreading and may cause a distinctly painful “razor blade throat,” public health experts currently assess the overall risk as low, and existing vaccines are expected to offer protection against severe outcomes. However, staying informed about symptoms, monitoring local spread data, and consulting healthcare providers about vaccination remain important steps amidst evolving public health landscapes.
