NB.1.8.1 variant triggers global COVID-19 surge amid endemic transition

As of May 29–30, 2025, global health authorities have confirmed that a new COVID-19 subvariant—NB.1.8.1—is driving a measurable resurgence of cases across several continents. The World Health Organization (WHO) classified NB.1.8.1 as a Variant Under Monitoring (VUM) in its late-May report, citing rapid international spread, potential immune escape mutations, and elevated transmission patterns.

The subvariant, a descendant of the Omicron XBB lineage, has been detected in over 22 countries to date. The highest concentrations of sequenced cases have emerged in China, Australia, and the United States, with early signs of upward pressure on hospital systems in some regions. This latest development underscores that COVID-19, despite having moved into the endemic phase, continues to evolve and test the adaptability of global health infrastructures.

Where Is NB.1.8.1 Spreading Most Rapidly?

In China, NB.1.8.1 is now the predominant variant in active circulation, according to genomic sequencing data shared by provincial health authorities in Guangdong and Zhejiang. Multiple hospitals in Shanghai and Beijing have reported surges in outpatient visits for flu-like symptoms, with mild-to-moderate COVID-19 illness making a marked comeback.

Australia has recorded one of the sharpest spikes, with NB.1.8.1 responsible for over 44% of recent case growth in Victoria, according to the Victorian Department of Health. New South Wales and Western Australia have also flagged the variant as a concern, triggering renewed public health advisories.

In the United States, the Centers for Disease Control and Prevention (CDC) confirmed NB.1.8.1’s presence in inbound travelers screened at airports in California, New York, Washington, and Virginia. While local transmission remains low—under 20 confirmed domestic sequences as of May 27—the CDC is expanding wastewater surveillance and port-of-entry monitoring.

Elsewhere, rising cases have also been reported in parts of Southeast Asia, the Middle East, and Southern Europe, particularly in tourist-heavy zones ahead of the summer travel season.

What Are the Symptoms and How Does NB.1.8.1 Compare to Earlier Variants?

Clinically, NB.1.8.1 presents with symptoms largely similar to Omicron and its subvariants. These include sore throat, mild fever, runny nose, dry cough, fatigue, and muscle aches. Some patients have also experienced gastrointestinal symptoms such as bloating and short-term nausea. Hospital systems in China and Thailand have noted that elderly individuals with comorbidities remain the most vulnerable to complications.

The variant’s distinguishing feature lies in its spike protein mutations, which enhance its ability to bypass immunity from prior infection or vaccination. However, as of late May, no evidence has emerged suggesting increased virulence or higher mortality risk. WHO scientists have reiterated that hospitalisation spikes appear to stem more from transmission volume than severity.

Global Testing, Surveillance, and Positivity Rates Rising Again

According to WHO’s COVID-19 dashboard, the global test positivity rate reached 11% in the week ending May 26—matching levels last observed during the KP.2-driven mini-wave of July 2024. While testing has declined significantly in most countries, the rise in positivity indicates elevated community spread in multiple regions.

India has also registered localized surges, particularly in Kerala, Tamil Nadu, and Maharashtra. On May 27, the Union Health Ministry confirmed over 1,000 active cases nationally, with Kerala alone accounting for more than 430. The Indian SARS-CoV-2 Genomics Consortium (INSACOG) has resumed targeted sequencing in urban clusters where reinfections and post-vaccination cases have increased.

Thailand, the Maldives, and parts of the UAE have similarly recorded sharp upswings in test positivity, prompting revised travel advisories and temporary testing mandates for incoming travelers from affected regions.

Are Vaccines Still Effective Against NB.1.8.1?

According to updated guidance from the WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC), existing mRNA and inactivated vaccines offer meaningful protection against severe illness caused by NB.1.8.1. However, waning antibody responses and the variant’s immune evasion characteristics make booster campaigns essential.

In the U.S., the Food and Drug Administration has requested that updated fall 2025 booster shots target the LP.8.1 and JN.1 lineages. Pfizer and Moderna are currently developing monovalent formulations for emergency rollout pending further variant analysis. The European Medicines Agency is conducting parallel assessments on whether NB.1.8.1 warrants modification to scheduled bivalent vaccine production.

India’s Bharat Biotech and Serum Institute have initiated laboratory assays to determine neutralization efficacy of existing Covaxin and Covishield lots against NB.1.8.1, with results expected by mid-June.

Institutional Sentiment and Economic Implications

While global markets have largely shrugged off the resurgence, institutional investors are beginning to price in mild disruptions to tourism, air travel, and pharmaceutical supply chains—especially in Asia-Pacific trade corridors. Shares of diagnostic testing companies and vaccine producers saw modest gains on May 28, with Moderna and Sinopharm posting early upticks on expectations of renewed demand.

Travel operators in Southeast Asia and Southern Europe are bracing for possible summer slowdowns if governments reimpose pre-boarding testing or health declaration requirements. The International Air Transport Association (IATA) has advised carriers to remain flexible as the variant’s trajectory becomes clearer.

In a May 29 briefing, the International Monetary Fund (IMF) noted that while the NB.1.8.1 impact is “currently limited,” its emergence is a reminder that structural readiness and real-time disease surveillance remain critical to global economic stability.

Are Public Health Measures Being Reintroduced?

No national lockdowns or school closures have been announced as of May 30, but countries are adopting preventive strategies. In Australia, Victoria’s Health Minister has reinstated mask advisories for hospitals and aged-care facilities. In China, cities like Hangzhou and Nanjing have advised large offices to shift to hybrid work setups for the next two weeks.

The CDC in the United States has advised immunocompromised individuals and the elderly to receive updated boosters once available and to consider masking in high-risk settings. No travel restrictions have been issued, but monitoring continues.

India has not imposed new restrictions but has reactivated its COVID-19 war rooms in Mumbai and Chennai to coordinate hospital readiness and data monitoring.

Future Outlook: Will This Be a Summer Wave or a Flash Flare?

Public health officials remain cautiously optimistic that NB.1.8.1 will not trigger a repeat of earlier pandemic waves. WHO’s current risk assessment deems the variant “low to moderate” in terms of public health impact, due to its lack of increased severity. However, that designation could change if recombination with other circulating variants occurs.

Leading virologists, including Dr. Maria Van Kerkhove of the WHO, have reiterated that countries must maintain “flexible vaccination and surveillance systems” to prevent avoidable mortality and disruption. The real threat may not be NB.1.8.1 itself, but the complacency it could breed in populations fatigued by four years of pandemic life.

As the world enters another summer of post-pandemic normalization, health systems are tasked with striking a balance between endemic stability and outbreak responsiveness. Whether NB.1.8.1 becomes a footnote or a flashpoint may depend less on the virus—and more on how nations choose to respond.