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As the world continues to grapple with the COVID-19 pandemic, new variants of the virus have emerged, raising concerns about their potential impact on public health. One such variant is the Omicron XBB.1.5, a sublineage of the XBB variant. This variant has been reported in 38 countries, with the majority of cases coming from the United States (82.2%), the United Kingdom (8.1%), and Denmark (2.2%).
The World Health Organization’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, the variant may contribute to increases in case incidence globally. However, the overall confidence in this assessment is low as growth advantage estimates are currently only available from one country, the United States.
To better understand the potential risks associated with XBB.1.5, WHO and TAG-VE have recommended that member states prioritize the following studies:
- 1. Analysis of growth advantage from additional countries where XBB.1.5 has been detected
- 2. Neutralization assays using human sera representative of the affected communities and XBB.1.5 live virus isolates
- 3. Comparative assessment to detect changes in rolling or ad hoc indicators of severity
Regarding growth advantage, national weekly growth advantage has been reported in the United States, with regional differences within the country. In the northeast part of the United States, there has been a rapid increase in proportion, from 1% in week 47 to 8% in week 50. However, it is important to note that data on growth advantage is currently only available from one country, so confidence in a global assessment is low.
Regarding antibody escape, XBB* variants, including XBB.1.5, are among the most antibody-resistant variants to date. Using pseudotyped virus neutralization assays, XBB.1.5 is equally immune evasive as the Omicron subvariant with the highest immune escape to date. These data have shown that sera from individuals with a) BA.1, b) BA.5 or c) BF.7 breakthrough infection and three doses of the inactivated vaccine (Coronavac) or d) BA.5 infection following three or four doses of mRNA vaccine (BNT162b2 or mRNA-1273) do not induce high neutralization titers against XBB.1.5. However, there is currently no data on real-world vaccine effectiveness against severe disease or death.
There is currently no data available in terms of severity and clinical considerations. Severity assessments are ongoing, and XBB.1.5 does not carry any mutation associated with potential severity changes.
In conclusion, the Omicron XBB.1.5 variant is a sublineage of the XBB variant reported in 38 countries, with the majority of cases coming from the United States, the United Kingdom, and Denmark. While early growth rate estimates suggest that this variant may contribute to increases in case incidence globally, the overall confidence in this assessment is low as growth advantage estimates are currently only available from one country. WHO and TAG-VE have recommended that member states prioritize studies to understand better the potential risks associated with XBB.1.5. As more data becomes available, the rapid risk assessment will be revised accordingly.
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