New Covid strains are sparking fresh health concerns across the globe as the world welcomes 2023. Descendants of the highly-transmissible Omicron variant - XBB and XBB.1.5 - have seen a surge in cases in many countries over winter. But what exactly are they? XBB is a subvariant of the Omicron BA.2 variant, and XBB.1.5 is a subvariant of XBB. Japanese researchers have studied XBB's characteristics, and results suggest that the subvariant is highly transmissible and has developed resistance to immunity. Countries including the UK, US, China, India, Pakistan and Australia have all reported cases of XBB and XBB.1.5. Watch more videos at the Independent TV: https://www.independent.co.uk/tv/editors-picks Click here to subscribe to The Independent: https://bit.ly/Subscribe-to-Independent About The Independent: Making Change Happen. The Independent is the world’s most free-thinking newsbrand, providing global news, commentary and analysis for the independently-minded. Connect with The Independent: Check out our full video catalog: null Videos, daily editorial and more: http://www.theindy.com/ Click here to get the best of The Independent daily: https://www.independent.co.uk/newsletters Like The Independent on Facebook: https://www.fb.com/TheIndependentOnline Follow The Independent on Twitter: https://twitter.com/Independent Follow The Independent on Instagram: https://www.instagram.com/the.independent Download the iOS & Android app: https://www.independent.co.uk/subscribe/app Help to support truly independent journalism. Every dollar you contribute will directly fund additional special reports and investigations from a free-thinking, award-winning newsroom you can trust - https://www.independent.co.uk/donations Subscribe to Independent Premium for exclusive content & live events: https://bit.ly/2MiOONB