The Global Virus Network (GVN) is closely monitoring the emergence of a newly identified SARS-CoV-2 variant, NB.1.8.1, a sublineage of the Omicron family. This variant was first identified in January 2025 and has rapidly spread across Asia and into other regions, including parts of the United States. The World Health Organization (WHO) has designated NB.1.8.1 as a Variant Under Monitoring due to its increasing prevalence and potential public health implications. Based on current evidence, GVN advises vigilance, not alarm, and reinforces the critical role of vaccination in preventing severe disease and death.
Similar to previous Omicron subvariants, NB.1.8.1 contains spike protein mutations associated with increased transmissibility. However, no evidence suggests that NB.1.8.1 causes more severe illness or significantly evades vaccine-induced or natural immunity. Early laboratory and clinical data indicate that updated COVID-19 vaccines, including bivalent and XBB-based boosters, protect against severe outcomes such as hospitalization and death. There is no evidence at this time that NB.1.8.1 causes more severe illness than previous variants.
Breakthrough infections may occur, particularly among individuals with waning immunity or those who are unvaccinated. Nevertheless, vaccines remain highly effective in reducing serious illness and death. Antiviral treatments such as nirmatrelvir/ritonavir (Paxlovid) and remdesivir demonstrate efficacy against a range of Omicron subvariants, including BQ.1, BQ.1.1, and XBB.1.5.
NB.1.8.1 has been linked to significant increases in COVID-19 cases across several countries. According to the WHO, as of May 18, 2025, the NB.1.8.1 variant has been identified in 22 countries, accounting for 10.7% of global SARS-CoV-2 sequences submitted to the Global Initiative on Sharing All Influenza Data (GISAID) during epidemiological week 17 (April 21–27, 2025). This marks a significant increase from 2.5% four weeks prior.
