The United States is seeing a sharp rise in COVID-19 cases linked to a new variant called XFG, or “Stratus,” which has become the third-most common strain this summer. First detected in Southeast Asia in January 2025, XFG was almost non-existent in the US until May. But cases began climbing in April, reaching 2%, then 6% in late May, 11% in early June, and 14% by the end of June, according to the Centers for Disease Control and Prevention (CDC).
States with high or very high levels of XFG include Alabama, Alaska, California, Delaware, Florida, Hawaii, Kentucky, Louisiana, and Texas. Cases are also rising in many others, including New York, New Jersey, Pennsylvania, Georgia, and Washington.
Another variant, NB.1.8.1 or “Nimbus,” is also circulating widely and is known for causing extreme sore throats.
The World Health Organization (WHO) says XFG is a recombinant of two earlier lineages, LF.7 and LP.8.1.2, with the earliest known sample collected on January 27, 2025. It is currently classified as a variant under monitoring due to its increasing presence globally. Experts believe the variant’s mutations could help it evade immune responses, but WHO rates its overall public health risk as low.
“There is no evidence that XFG causes more severe illness or significantly different symptoms than previous Omicron variants,” said Subhash Verma, professor of microbiology and immunology at the University of Nevada, Reno. Approved COVID-19 vaccines are still expected to protect against severe disease caused by XFG.
The CDC lists common symptoms of XFG as fever or chills, cough, shortness of breath, sore throat, congestion, loss of taste or smell, fatigue, body aches, headache, and nausea. Health experts continue to monitor the variant closely as it spreads across the US and Europe.
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Shivam Verma is a journalist with over three years of experience in digital newsrooms. He currently works at NewsX, having previously worked for Firstpost and DNA India. A postgraduate diploma holder in Integrated Journalism from the Asian College of Journalism, Chennai, Shivam focuses on international affairs, diplomacy, defence, and politics. Beyond the newsroom, he is passionate about football—both playing and watching—and enjoys travelling to explore new places and cuisines.
