Thailand’s Department of Disease Control confirmed today, June 3, that the Covid-19 NB.1.8.1 variant has remained the country’s dominant strain since mid-2025, but officials have found no evidence that it causes more severe illness than earlier variants.
DDC director-general Dr Montien Kanasawat said the Ministry of Public Health continues to monitor Covid-19 and changes in the SARS-CoV-2 virus through the Digital Disease Surveillance system, event-based monitoring, and laboratory surveillance.
Data from the DDS system on June 2 recorded 4,156 Covid-19 cases and one death. The highest number of infections was found among people aged 30 to 39, followed by those aged 60 and above, and people aged 20 to 29.
Montien said cases have risen seasonally over the past month, but the number remains below the five-year median.
Variant surveillance by the Department of Medical Sciences between January 1, 2025, and April 23, 2026, found NB.1.8.1 accounted for 50.95% of detected strains in Thailand. JN.1 followed at 24.97%, while XEC accounted for 9.14%.
Montien said NB.1.8.1 has mutations that may help it spread and evade immunity, but current data does not show more severe symptoms or higher death risk than earlier strains.
Most patients still show symptoms similar to common respiratory infections, including fever, cough, sore throat, and runny nose.
Thailand continues to monitor respiratory infections through a network of 26 sentinel hospitals nationwide. The system covers Covid-19, influenza, and other viral respiratory infections.
Samples from patients who meet surveillance criteria are tested systematically. If unusual signs or potentially significant changes are found, the samples are sent to the Department of Medical Sciences for further variant identification and risk assessment.
DDC deputy director-general Dr Direk Khampaen said officials have not found signs of widespread outbreaks beyond previous seasonal trends.
He said Covid-19 remains a respiratory infection that can be found throughout the year, especially during the rainy season, when people are more likely to gather indoors.
The DDC advised people to maintain personal hygiene, wash their hands regularly, wear a face mask in crowded places or when they have respiratory symptoms, and avoid close contact with sick people.
People with fever, cough, sore throat, or a runny nose should take an initial screening test and avoid close contact with high-risk groups, including elderly people, people with underlying illnesses, and pregnant women.
Anyone seeking more information can contact the DDC hotline on 1422.
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