Overview

• First detected in January 2025, NB.1.8.1 was designated a variant under monitoring on May 23 after its share of global sequences rose from 2.5% to 10.7% by late April.
• The variant has overtaken other strains to become dominant in Hong Kong and China and has been identified in over 20 countries including Thailand, the UK and Australia.
• In California, NB.1.8.1’s prevalence climbed from roughly 2% to 19% of cases since April with detections reported in multiple US states pending formal CDC tracking.
• WHO rates the variant’s global risk as low and expects current COVID-19 vaccines to remain effective against severe disease while advising against travel or trade restrictions.
• Public health authorities in Thailand and across the US are urging masks, handwashing, booster shots and swift medical care for symptoms similar to other Omicron subvariants.