Cases of Covid-19 have risen sharply across the UK this month, driven largely by a variant of the virus known as ‘XFG’.

Sometimes referred to as ‘Stratus’ and the ‘American strain’, owing to the fact that it is now the most common strain in North America, it was first identified in January 2025 and has since spread worldwide.

Between August and September, Covid cases in Britain jumped 230 per cent, from 1,374 to 4,589 new infections, half of which were caused by the XFG strain.

Hospitalisation rates have also increased by 15 per cent in the same period, according to the UK Health Security Agency (UKHSA).

The true number of cases is likely to be much higher, as most people who contract Covid-19 experience a milder illness and will not visit hospital or receive an official diagnosis via their GP.

What are the symptoms, and how is it different from other variants?

Symptoms of XFG are similar to other variants of Covid-19 like Delta and Omicron, and typically begin with a sore throat, before developing…