According to the Ho Chi Minh City Department of Health, 83% of Covid-19 patients recently tested carry the NB.1.8.1 variant - a sublineage of the Omicron JN.1 strain currently circulating in more than 20 countries including the U.S., Canada, Australia, China, Japan, and South Korea.

Gene sequencing data from the Hospital for Tropical Diseases and the Oxford University Clinical Research Unit (OUCRU) show that this subvariant accounted for the majority of cases hospitalized during the third week of May 2025. NB.1.8.1 was first identified earlier this year and has shown signs of heightened transmissibility.

According to the city’s infectious disease surveillance system, Covid-19 cases began to rise from weeks 16 to 20 (April 14 to May 18), with an average of 11 cases per week - up from just 1–2 weekly in the first 15 weeks of the year. In week 20 alone, 26 new cases were recorded, a 16-case increase over the previous four-week average.

As of mid-May, Ho Chi Minh City has logged 79 Covid-19 cases in 2025, a 75.5% decrease compared to the same period in 2024. Of these, 43 were hospitalized and 36 were outpatient cases, with no serious illnesses or respiratory complications.

In response, the Health Department on May 21 urged hospitals and medical centers to prepare for possible outbreaks, ensure timely detection and treatment of severe cases, and prioritize protection of high-risk groups. The HCMC Center for Disease Control (HCDC) is also working with OUCRU to monitor case trends and variants, and to propose appropriate prevention measures.

The Department of Health advises residents not to panic, but to adhere to Ministry of Health guidelines: wear masks in public, wash hands regularly, avoid large gatherings, maintain good health, and seek medical care when experiencing symptoms such as fever, cough, or shortness of breath. Travelers from high-case countries should monitor their health closely.

Characteristics of NB.1.8.1

Although not currently classified as a variant of concern by the World Health Organization (WHO), NB.1.8.1 is a new Omicron subvariant with an elevated transmission rate.

Preliminary data suggest NB.1.8.1 binds more effectively to human cells than previous strains, increasing its contagiousness. Symptomatically, it mirrors earlier Omicron variants, with patients commonly reporting sore throat, fatigue, mild fever, body aches, nasal congestion, and cough. Some cases experience prolonged low-grade fever, as well as headaches, nausea, appetite loss, and digestive discomfort.

Despite its rapid spread, there is no current evidence that NB.1.8.1 causes more severe illness than existing variants of SARS-CoV-2.

Phuong Thuy