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Home Media Article for health COVID-19 "Nimbus" NB.1.8.1: Fast-Spreading Variant

COVID-19 "Nimbus" NB.1.8.1: Fast-Spreading Variant

May 28 / 2026

nimbus covid

 

 

     The COVID-19 pandemic situation has returned to the spotlight following the detection of a new subvariant named NB.1.8.1 or “COVID Nimbus,” which is currently causing an increase in outbreaks across several regions, particularly in Singapore and Thailand. This article summarizes key information to help you understand and prepare appropriately.

 

About the Disease: What is NB.1.8.1?

     NB.1.8.1, also known as "Nimbus," is an Omicron subvariant that evolved from the recombinant lineage XDV.1.5.1 and is linked to the JN.1 group. It was first detected in January 2025 and was declared by the World Health Organization (WHO) as a Variant Under Monitoring (VUM) on May 23, 2025.

 

Key Characteristics

     The defining feature of NB.1.8.1 is multiple mutations on its spike protein, which allow the virus to bind more tightly to human cells and better evade immunity. This contributes to its rapid transmission. However, there is currently no evidence indicating that this variant causes more severe symptoms compared to previous strains. (European Centre for Disease Prevention and Control, 2025)

 

  • Significant Mutations: It possesses 7 additional mutations on the spike protein compared to the JN.1 variant (such as S:A435S, S:V445H, S:T478I). The mutation at position 445 helps the virus bind more securely to human cells, while position 478 allows it to evade certain types of immune responses more effectively than before.

     

  • Statistics in Thailand: In Thailand, NB.1.8.1 rapidly became the dominant strain during April and May 2025, accounting for more than half of tested samples, despite not being detected at all at the beginning of the year.

 

 

Symptoms: "Sore throat like swallowing razor blades"

Symptoms for individuals infected with NB.1.8.1 are mostly mild, but a frequently reported specific characteristic is:

 

  • Severe Sore Throat (Razor-blade throat): Patients often report a sharp, severe pain in the throat, describing it as feeling like swallowing razor blades.
  • General Symptoms: Fever, fatigue, dry cough, muscle aches, nasal congestion, or a runny nose.
  • What Has Changed: Symptoms like loss of taste and smell are much less common with this variant.

 

 

COVID Nimbus

 

 

Vulnerable Groups Requiring Monitoring

Although recent reports in Thailand indicate that the majority of patients are within the working-age population (ages 20-29 and 30-35 years), there are other vulnerable groups that still require close monitoring:

 

  • The elderly
  • Individuals with underlying medical conditions
  • Infants and children aged 6 months and above, including older children and teenagers
  • Pregnant women, as they face a mortality rate up to 3 times higher than the general population. Vaccination during pregnancy also helps pass protective antibodies to the baby, protecting them for up to 6 months after birth.

 

 

Diagnosis and Testing

     Despite the virus's mutations, initial screening using ATK (Antigen Test Kit) remains effective. If symptoms such as fever, cough, or a runny nose develop, a test should be performed immediately. If the result is positive—especially for those in high-risk groups—a physician should be consulted for further diagnosis. At the laboratory level, public health agencies continue to utilize genetic sequencing to closely monitor strain changes.

 

 

Reference

 

 

 

 

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