- Classification: Classified as a Variant Under Monitoring (VUM) by the WHO (officially designated on May 23, 2025).1
- Lineage: A descendant of the Omicron lineage (specifically a sub-lineage derived from XBB or JN.1).2
- Emergence & Spread:
- First detected in January 2025 (originating in China/Asia).3
- Reported in 22+ countries by mid-May 2025.4
- Showed a rapid growth advantage, accounting for approximately 10.7% of sequenced cases globally in late April 2025 (up from 2.5% four weeks prior).5
- Signature Symptom: The distinct, severe throat pain described anecdotally as “razor blade throat,” often felt sharply when swallowing.6
- Severity & Risk:
- Transmissibility: Considered highly transmissible due to spike protein mutations that enhance binding to the ACE2 receptor.7
- Severity: Current data do not indicate that Nimbus causes more severe illness, hospitalization, or death compared to other circulating Omicron variants.8
* **Immunity:** While it shows marginal **immune evasion** against existing antibodies, current COVID-19 vaccines (including updated boosters) are **still expected to protect against severe disease and hospitalization**.
This variant drew attention primarily for its aggressive spread and the intensity of the sore throat symptom, rather than for causing increased overall disease severity.
You can learn more about the public’s experience with the variant’s key symptom here: “Razor blade throat” COVID? What to know about new “Nimbus” variant.