Stratus and Nimbus Lead UK Covid Infections

Two newly named Omicron subvariants have become the most common causes of Covid-19 infection in the United Kingdom, health authorities said, as cases and hospital admissions edge higher. Data from the UK Health Security Agency for the week to September 21 show XFG, nicknamed Stratus, accounted for about one third of sequenced infections, while NB.1.8.1, known as Nimbus, made up just over 10 percent of cases.

Both variants were first detected earlier this year. Stratus was identified in a sample dated January 27, 2025, and is a recombinant of earlier lineages. Nimbus was first detected on January 22, 2025. The World Health Organization has designated Stratus a variant under monitoring after several countries in Southeast Asia reported rises in cases and some increases in hospitalisations in areas where the variant was found.

The UK is experiencing a mild uptick in indicators of viral activity. The proportion of positive tests reported rose from 7.6 to 8.4 over a recent week, and hospital admissions increased from 2.00 to 2.73 per 100,000, according to the UKHSA. The WHO has said current data do not indicate these variants cause more severe illness, adding that monitoring and...