WHO adds NB.1.8.1 to global variant monitoring list as spread confirmed in 22 countries

The World Health Organization officially designated NB.1.8.1 as a Variant Under Monitoring (VUM) on May 23, 2025, after detecting its spread across at least 22 countries and confirming its presence in multiple global regions, including the Americas, Southeast Asia, and Europe. WHO’s Technical Advisory Group on SARS-CoV-2 Virus Evolution (TAG-VE) determined that the variant’s spike mutations warranted early-stage tracking, despite no current evidence of increased disease severity or vaccine evasion.

The classification places NB.1.8.1 into WHO’s first-tier category of variant monitoring, used to flag lineages with early signs of potential public health relevance. NB.1.8.1, a recombinant strain in the JN.1 lineage family, was first identified in early 2025 and has since shown consistent growth in genomic prevalence, particularly in nations with strong border screening infrastructure.

What Are the Mutations That Make NB.1.8.1 Noteworthy?

Virologists involved in WHO’s assessment report that NB.1.8.1 contains a cluster of notable spike protein mutations, including T22N, F59S, G184S, A435S, V445H, T478I, and Q493E. These alterations may affect both the variant’s binding affinity to human ACE2 receptors and its resistance to antibody neutralization. According to preliminary data reviewed by WHO, NB.1.8.1 demonstrates a 1.5 to 1.6-fold reduction in neutralization by sera from previously vaccinated or infected individuals when compared to LP.8.1.

While this immune evasion is not yet considered significant, WHO has highlighted these mutations as a reason for enhanced genomic and serological surveillance through the CoViNet system. TAG-VE emphasized that growth advantage, not clinical severity, was the primary driver behind the VUM classification.

How Does WHO Track Variants Like NB.1.8.1 in 2025?

WHO’s variant monitoring system is structured around a three-tier classification: Variants Under Monitoring (VUM), Variants of Interest (VOI), and Variants of Concern (VOC). VUMs are designated when genetic changes in the virus raise concerns but lack sufficient epidemiological evidence. This stage allows health agencies to intensify sequencing and collect data before deciding whether to elevate a variant’s status.

All classifications are maintained and reviewed by the TAG-VE, which evaluates genomic, clinical, and epidemiological evidence on a rolling basis. NB.1.8.1 met VUM criteria due to its growth trend, spike mutation pattern, and early detections in geographically distant regions, from North America to Southeast Asia.

What Is CoViNet and How Does It Support Global Surveillance?

To support timely identification and tracking of new COVID-19 variants, WHO launched the Coronavirus Variant Network (CoViNet) in 2023. As of 2025, CoViNet includes more than 60 partner laboratories across six WHO regions, enabling decentralized, real-time sharing of variant sequencing data and immunological response analyses.

In India, CoViNet collaboration is managed through CSIR-NEERI (Council of Scientific and Industrial Research – National Environmental Engineering Research Institute), which is a WHO collaborating center. The institute, along with the Indian SARS-CoV-2 Genomics Consortium (INSACOG), played a key role in detecting NB.1.8.1 through wastewater surveillance in Tamil Nadu in April 2025. This type of environmental surveillance is becoming a critical early warning tool, particularly as traditional clinical testing rates decline globally.

Where Has NB.1.8.1 Been Detected So Far?

As of late May 2025, NB.1.8.1 has been reported in at least 22 countries. U.S. health officials confirmed detections via airport-based sequencing in California, New York, Virginia, and Washington. While the Centers for Disease Control and Prevention (CDC) has not yet elevated NB.1.8.1 to its public dashboard, internal assessments are ongoing.

In India, INSACOG confirmed NB.1.8.1 sequences in Tamil Nadu and is currently conducting surveillance for wider community transmission. Singapore and Malaysia have also reported increasing detections, particularly in border regions. Germany, the United Kingdom, and Italy have identified the variant through international traveler screening and post-arrival testing programs.

What Are WHO and National Agencies Saying About the Risk?

The WHO, in its May 23 risk evaluation bulletin, stated that NB.1.8.1 poses a low global public health risk at this time, with no evidence suggesting increased hospitalization, ICU admission, or mortality. However, the agency underlined the importance of proactive monitoring due to the variant’s expansion and potential genetic divergence from existing vaccine coverage.

The CDC has echoed WHO’s stance, emphasizing that continued booster campaigns—especially for vulnerable populations—remain essential. India’s Ministry of Health and Family Welfare has issued internal guidance to state health departments to review their sequencing protocols and increase sample submissions to INSACOG.

Why Does Monitoring Emerging Variants Still Matter in 2025?

Although the acute pandemic phase has ended, SARS-CoV-2 remains a mutating respiratory pathogen that can evolve unpredictably. Variant surveillance is crucial to ensure that public health tools—including diagnostics, therapeutics, and vaccines—remain effective. WHO’s VUM-to-VOC tracking structure is designed to offer layered, data-informed responses based on changing evidence.

Variants like NB.1.8.1 that show early signs of growth or unusual mutational patterns provide global health agencies with opportunities to intervene before major community outbreaks occur. Moreover, the identification of such variants in international traveler populations suggests a potential for future displacement of dominant strains.

What Comes Next in the Global Response?

The WHO has urged member states to maintain genomic sequencing and integrate variant surveillance into routine public health infrastructure. CoViNet partners are being asked to prioritize sequencing of NB.1.8.1 samples and share results promptly with regional coordinating hubs. The WHO will reassess NB.1.8.1’s designation in mid-June based on new epidemiological data.

In the meantime, national governments are advised to continue monitoring hospitalization trends and clinical severity patterns, particularly among unvaccinated individuals and those with comorbidities. Should NB.1.8.1 exhibit stronger immune escape or clinical effects, its classification may be escalated to a VOI or VOC.