The World Health Organisation and the UK Health Security Agency (UKHSA) both placed BA.2.86 on their monitoring lists on Thursday because of the high number of mutations it carries.
Its discovery has amplified fears of a new wave of Covid in the UK. Hospital admissions for coronavirus have risen in the past month, coinciding with the effectiveness of vaccines wearing off and a new variant emerging.
At the same time, ministers have decided Covid boosters will not be offered to nearly 12 million Britons this winter.
Most healthy adults under 65 will not be eligible for a booster, the Joint Committee on Vaccination and Immunisation advised, and the government accepted.
Last autumn, all over-50s were invited for a jab, but eligibility has been tightened this year.
According to official data, as of last Saturday, there were an extra 930 Covid cases in England compared with the previous week.
Dr Meera Chand, deputy director of UKHSA, said: “We’re aware that BA.2.86 has been detected in the UK. UKHSA is assessing the situation and will provide further information in due course.”
So far, three cases of the new BA.X strain, which is also known as BA.2.86, have been detected in Denmark and Israel, and later a fourth was found in Michigan in the US.
The strain has more than 30 mutations on its spike protein – more than other circulating variants, which is thought to have prompted the WHO to escalate it swiftly.
Luke Blagdon Snell, a clinical research fellow at King’s College London, said a patient at Guy’s and St Thomas’ in the capital had first shown symptoms five days ago, and had acquired the infection “locally”.
Kristian G Andersen, an immunologist and infectious diseases expert, said the lineage had all the hallmarks of something that could take off, but added: “Our immunity landscape is now complex, so it’s too early to say it will.”
Dr S. Wesley Long, medical director of diagnostic microbiology at Houston Methodist, a flagship Texan hospital, said it remained to be seen whether BA.2.86 would be able to out-compete other strains of the virus or have any advantage in escaping immune responses from prior infection or vaccination.
The US Centers for Disease Control and Prevention, which is monitoring the variant, wrote: “As we learn more about BA.2.86, CDC‘s advice on protecting yourself from Covid-19 remains the same.”
Symptoms of the new variant include a runny nose, headache, fatigue, sneezing and a sore throat.
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