What is NB.1.8.1? India’s new Covid variant explained

The NB.1.8.1 sub-variant, which descends from the recombinant lineage XDV.1.5.1, was first identified globally in January 2025

India has detected a new sub-variant of Covid-19, NB.1.8.1, which has been classified by the World Health Organization (WHO) as a 'Variant Under Monitoring' (VUM) as of May 2025. The variant, linked to the Omicron lineage JN.1, was identified from a sample collected in Tamil Nadu and submitted to India’s SARS-CoV-2 genome sequencing consortium, INSACOG, in April.

According to health authorities and initial global data, NB.1.8.1 appears to carry spike protein mutations that suggest higher transmissibility and a degree of immune evasion, although it is not currently considered a Variant of Interest or Concern.

The NB.1.8.1 sub-variant, which descends from the recombinant lineage XDV.1.5.1, was first identified globally in January 2025. According to The Indian Express, it has six mutations in its spike protein compared to another variant called LP8.1, and eight mutations compared to JN.1. Some of these mutations — named A435S, V445H, and T478I — may help the virus stick more easily to human cells, possibly making it spread more easily.

So far, 58 cases of the NB.1.8.1 Covid-19 variant have been recorded in global genome databases from 22 different countries. These include the United States, Japan, South Korea, Thailand, and Singapore. In the U.S., the variant was identified through airport screenings in states such as California, Washington, Virginia, and New York.

Early data from China and Southeast Asia indicate that the NB.1.8.1 variant is spreading rapidly in certain areas. In Singapore, for example, weekly COVID-19 cases rose from 11,100 to more than 14,000 in early May. However, the variant has not yet become the most common strain in most places.

The NB.1.8.1 variant presents symptoms similar to earlier Omicron strains—such as sore throat, mild fever, fatigue, nasal congestion, headache, stomach-related issues, reduced appetite and nausea. Although loss of taste or smell, once common with variants like Delta, is now rarely observed.

As of May 19, India has 257 active Covid-19 cases, with slight rises in Kerala (273 cases in May), Maharashtra, and Tamil Nadu. The NB.1.8.1 variant remains rare, while the JN.1 sub-variant continues to be the most common, accounting for 53% of sequenced samples, followed by BA.2 at 26%.

Both the WHO and Indian health authorities have indicated that NB.1.8.1 does not appear to cause more serious illness or lead to higher rates of hospitalization or death. Most infections have been mild and managed at home, with few hospital admission.

Although NB.1.8.1 is being carefully monitored, experts say there’s no need to worry right now. Vaccination, ongoing genome tracking, and prompt reporting continue to be important in managing and controlling the virus as it changes.