NB.1.8.1 triggers COVID crisis in Hong Kong—Global agencies on high alert

Hong Kong is experiencing its most severe COVID-19 hospitalization wave in over a year, according to newly released data from the Centre for Health Protection and the Hospital Authority. Officials have linked the ongoing surge to the rapid spread of NB.1.8.1—a subvariant of the Omicron JN.1 lineage that was added to the World Health Organization‘s Variant Under Monitoring (VUM) list on May 23. In just four weeks, the city has recorded 81 severe COVID-19 cases and 30 related deaths, a majority of them in residents aged 70 and above.

The outbreak marks the most acute COVID resurgence in Hong Kong since the BA.5 and XBB waves in 2022–2023, which had strained ICU capacity and driven high mortality in aged care facilities. While population-level immunity has since increased, health authorities now acknowledge that waning booster protection and public complacency may be leaving elderly residents exposed to emerging variants.

What Makes NB.1.8.1 a Variant of Concern in Practice?

NB.1.8.1, a descendant of JN.1 and sibling to LP.8.1 (the current dominant U.S. variant), was first sequenced in early 2025 and rapidly gained share in genomic surveillance across Asia and North America. Its genetic profile includes several spike protein mutations—A435S, V445H, T478I, and Q493E—which are suspected to enhance both transmissibility and modest immune evasion.

WHO’s Technical Advisory Group on Virus Evolution (TAG-VE) noted in its latest bulletin that NB.1.8.1 shows a 1.5–1.6-fold reduction in neutralization capacity by antibodies derived from prior infection or vaccination. This places it within the range of known immune-evasive subvariants, although it is not currently linked to increased severity in most populations.

However, the concentration of deaths and ICU admissions in Hong Kong, particularly among unboosted elderly patients, has triggered heightened concern among epidemiologists and public health planners.

What Is the Situation in Hong Kong Hospitals?

Hong Kong’s public hospital system has reported a 25–30% surge in isolation ward and high-dependency unit occupancy in the past two weeks. The Hospital Authority said that while most cases remain mild or moderate, the number of daily ER visits has doubled since mid-April. Triage teams have reintroduced COVID-dedicated patient pathways, and several private hospitals have been advised to prepare contingency bed allocations.

Dr. Albert Au of the Centre for Health Protection told local media that “delayed booster uptake and low mask usage in elderly groups” were contributing factors to the surge. He also noted that many recent fatalities had occurred in residents with no COVID booster dose in the past 12 months, despite prior eligibility.

What Are the Symptoms and Clinical Pattern of NB.1.8.1?

NB.1.8.1 infections are symptomatically similar to earlier Omicron waves, with common signs including sore throat, mild fever, fatigue, nasal congestion, cough, and muscle aches. Physicians at Queen Mary Hospital and Prince of Wales Hospital have noted an increase in gastrointestinal complaints, such as nausea and diarrhea, especially in older adults.

While most vaccinated individuals continue to experience mild illness, clinicians warned of rapid oxygen desaturation in unvaccinated elderly patients or those with chronic heart and lung conditions. Medical staff have been advised to monitor high-risk individuals more closely during the first 48 hours of hospitalization.

What Are Hong Kong Authorities Doing in Response?

The government has not reinstated full-scale public health restrictions, but a mask advisory has been reissued for all public transit and indoor crowded spaces, particularly for elderly and immunocompromised individuals. Hospital visitor restrictions have been reactivated, and mobile vaccination outreach has resumed in nursing homes across Kowloon and the New Territories.

Hong Kong’s Secretary for Health, Lo Chung-mau, said in a press briefing that the administration is prioritizing booster campaigns and genomic surveillance. He added that additional vaccine shipments have been secured to support a targeted summer immunization drive for adults over 65.

How Does This Compare to Previous COVID Waves in Hong Kong?

In March 2022, Hong Kong faced a deadly fifth wave dominated by the BA.2 subvariant, which overwhelmed healthcare systems and led to a record-high fatality rate per capita among global cities at that time. Since then, vaccine coverage has improved, with over 94% of the population having received at least two doses, but booster uptake has plateaued at around 39% among seniors according to recent government estimates.

Public health experts warn that Hong Kong’s demographics—specifically its aging population and densely populated urban housing—make it vulnerable to hospital system shocks during variant waves, even when overall infection rates are moderate.

Where Else Has NB.1.8.1 Been Detected?

Globally, NB.1.8.1 has now been confirmed in 22 countries, with cases rising in Singapore, China, Malaysia, the United States, and several EU nations. In the U.S., the Centers for Disease Control and Prevention (CDC) has identified the variant through airport screening in California, Washington, Virginia, and New York. Community transmission has also been detected in Ohio, Hawaii, and Rhode Island.

While the CDC has not yet added NB.1.8.1 to its COVID Data Tracker, officials have confirmed that internal assessments are ongoing, and more updates may follow in the June surveillance report.

How Are WHO and Global Agencies Reacting?

The World Health Organization classified NB.1.8.1 as a Variant Under Monitoring on May 23, citing a growing number of detections across continents and mutations linked to moderate immune escape. The WHO emphasized that current data does not suggest increased severity, but highlighted the need for continued sequencing, hospitalization tracking, and real-world vaccine effectiveness studies.

In the United States, the Food and Drug Administration (FDA) has endorsed a new monovalent vaccine targeting LP.8.1 for the fall 2025 booster campaign. Given the genetic proximity of LP.8.1 and NB.1.8.1, health experts believe that updated vaccines will likely offer cross-protection against both.

What Does This Mean for Global Preparedness?

The Hong Kong experience has offered a sobering reminder that COVID-19’s risk profile remains dynamic, particularly for elderly populations with lapsing immunity. While most countries have moved away from emergency declarations, WHO and regional agencies continue to warn that seasonal surges and regional flare-ups can still produce significant clinical and systemic impacts.

Public health officials in Japan, Australia, and the EU are monitoring the Hong Kong wave closely as they prepare for potential summer or early autumn increases, particularly in tourism-heavy regions with low booster coverage. The CDC, ECDC, and Singapore’s Ministry of Health have each reiterated calls for vaccine uptake, masking in high-risk settings, and data transparency in variant reporting.