Brits told to stick to 20-second rule as Covid variants XFG and NB.1.8.1 spreadThe advice comes as two variants of the infection are currently the most prevalent in the UK. View Image The UKHSA has issued advice on how to prevent the spread of Covid (Image: Getty)The UK Health Security Agency (UKHSA) has issued a 20-second warning to help curb the spread of Covid, as two variants of the infection are currently the most prevalent in the UK. ‌In an update, the UKHSA revealed that the most common variants in the UK at present are XFG and NB. ‌Currently, it is not believed that these variants cause more severe illness than other circulating variants. In addition, it offered advice for anyone who is unwell or experiencing Covid symptoms.