What is known about 'American Covid' strain which is on rise in the UK. The XFG variant of SARS-CoV-2, also known as "American Covid” strain, formed from two earlier Omicron subvariants, LF.7 and LP.8.1.2, WHO said. First detected on January 27, 2025, XFG symptoms include sore throat, cough, fatigue and fever. The strain is currently on the rise in UK, but health experts say there is no evidence that XFG causes more severe disease.