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XBB.1.5 Rapid risk assessment, 11 January 2023
The Omicron XBB.1.5 variant is a sublineage of XBB, which is a recombinant of two BA.2 sublineages. From 22 October 2022 to 11 January 2023, 5 288
sequences of the Omicron XBB.1.5 variant have been reported from 38 countries. Most of these sequences are from the United States of America
(82.2%), the United Kingdom (8.1%), and Denmark (2.2%).
WHO’s Technical Advisory Group on Virus Evolution (TAG-VE) met on 5 January 2023 to discuss the latest evidence on XBB.1.5 and assess the public
health risk associated with this variant. Based on its genetic characteristics and early growth rate estimates, XBB.1.5 may contribute to increases in
case incidence. To date, the overall confidence in the assessment is low as growth advantage estimates are only from one country, the United States
of America.
WHO and the TAG-VE recommend Member States to prioritize the following studies to better address uncertainties relating to the growth advantage,
antibody escape, and severity of XBB.1.5. The suggested timelines are indicative and will vary from one country to another based on national capacities:
• Analysis of growth advantage from additional countries where XBB.1.5 has been detected (1-3 weeks).
• Neutralization assays using human sera representative of the affected community(ies) and XBB.1.5 live virus isolates (2-6 weeks).
• Comparative assessment to detect changes in rolling or ad hoc indicators of severity (see table below, 4-12 weeks)
The rapid risk assessment below is based on currently available evidence and will be revised regularly as more evidence and data from additional
countries become available.
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