As many as six cases of Covid-19 cases of the highly-contagious Omicron subvariant category XBB were detected at a hospital in Pakistan’s Karachi city on Wednesday.The XBB cases were confirmed at Aga Khan University Hospital (AKUH) in Karachi, Dawn reported.”We have detected six cases, however, others have been found around the country,” AKUH Infectious Diseases Section Head Dr Faisal Mehmood told Dawn. “These have started since November.”The XBB is a highly contagious subvariant of COVID-19’s Omicron strain, according to the World Health Organisation (WHO). The XBB variant had a higher reinfection risk, as compared to other circulating Omicron sublineages, the Dawn report said.The Omicron subvariant XBB.1.5, a relative strain of the XBB variant, makes up to 40.5 per cent of new infections across the United States, The Hill reported last week, citing Centers for Disease Control and Prevention (CDC).According to the CDC, the XBB.1.5 Omicron subvariant has pushed out the BQ.1 and the BQ.1.1 subvariants from their previous positions as the most detected coronavirus mutations.The XBB subvariant, from which XBB.1.5 descends, is a recombinant of two subvariants that descended from the BA.2 omicron subvariant. That means it carries genetic data from two versions of the coronavirus that originated from the BA.2 subvariant, The Hill reported.Karachi’s Dr Mehmood said the XBB variant can spread rapidly in people who do not have pre-existing immunity from vaccination or previous infections.”The symptoms are similar to the other Covid variants,” he was quoted as saying by Dawn. The expert said adequate amounts of testing were the most important thing to counter the spread of the new variant.