NB.1.8.1: Emerging Covid-19 Sub-Variant
NB.1.8.1: Emerging Covid-19 Sub-Variant and Its Public Health Implications
A new sub-variant of Covid-19, named NB.1.8.1, has been identified in India and is gaining attention due to its potential for increased transmissibility. This strain is a descendant of the Omicron variant JN.1 and has prompted the World Health Organization (WHO) to classify it as a “Variant Under Monitoring” (VUM). Although it does not yet qualify as a “Variant of Interest,” its genetic features suggest the need for ongoing observation.
Origins and Genetic Evolution
NB.1.8.1 is believed to have emerged from the recombinant variant XDV.1.5.1. Its earliest known samples were detected in January 2025. What makes this variant notable is the number of mutations it carries in the spike protein region—six more than its related strain LP8.1 and eight more than JN.1. These genetic changes, particularly mutations such as A435S, V445H, and T478I, may allow the virus to bind more efficiently to human cells, potentially increasing its transmission rate and providing it with limited immune escape capabilities.
Symptoms and Clinical Presentation
The clinical symptoms associated with NB.1.8.1 remain similar to earlier Omicron sub-variants. Patients typically experience mild respiratory symptoms such as sore throat, fatigue, low-grade fever, nasal congestion, and mild cough. Gastrointestinal symptoms like nausea and mild abdominal discomfort have also been reported in some cases. Unlike the early strains of Covid-19, the hallmark symptom of loss of taste or smell is less frequently seen with this variant.
Geographical Spread and Impact
While the sub-variant is still under study, its spread has already been observed beyond India. In countries like China and Singapore, NB.1.8.1 appears to be spreading rapidly. Singapore, for instance, recorded an increase in weekly Covid-19 cases from approximately 11,000 to over 14,000 in early May 2025. In India, as of May 19, 2025, the number of active Covid-19 cases stood at 257, with slight upticks reported in states such as Kerala and Tamil Nadu. The dominant circulating variant remains JN.1, followed by BA.2, though NB.1.8.1 is being closely monitored for any shifts in dominance.
Case Study: Bengaluru Infant
One unique case that drew attention was a nine-month-old infant in Bengaluru who tested positive for Covid-19. The baby, who is reportedly stable, is undergoing treatment. This case has further highlighted the importance of vigilance, especially among vulnerable age groups.
Vaccination and Public Health Measures
Health experts currently believe that NB.1.8.1 does not lead to more severe disease than previous variants. Most cases are manageable at home with mild symptoms, and hospitalisation rates remain low. Preliminary assessments suggest that existing Covid-19 vaccines continue to offer protection against severe illness caused by this variant.
NB.1.8.1 serves as a reminder that the Covid-19 virus continues to evolve. Although not classified as a variant of concern, its potential for faster spread necessitates close surveillance. The public is urged to maintain preventive habits such as proper hygiene, mask-wearing in crowded spaces, and seeking medical advice if symptoms develop. With timely action and continued vaccine coverage, the public health impact of NB.1.8.1 can likely be contained.