Credit NIAID
#17,227
Citing a lack of data (see WHO: Countries Reporting COVID Data Continues To Decline), this week's RRA on the emerging XBB.1.5 Omicron variant leaves a lot of questions unanswered.
According to the WHO, both the quality, and quantity, of the available data is insufficient to gauge its ultimate impact.
In a nutshell, they report:
Based on its genetic characteristics and early growth rate estimates, XBB.1.5 may contribute to increases in case incidence globally. To date, the overall confidence in the assessment is low as growth advantage estimates are only from one country, the United States of America
But, as the following report indicates, it may be weeks before we have enough data to say - with any certainty - whether XBB.1.5 produces any greater severity of illness than previous Omicron variants, or whether it will spread globally as quickly as it has in the United States.
From this week's WHO Epidemiological Update (#125):
Annex 3. 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.
This assessment from early December looks at 3 characteristics of these variants (Growth advantage, Immune Escape, and Infection Severity) and found with moderate confidence that in two out of three categories (marked in red), these variants are `worse than BA.5'.
They also found (albeit with low confidence) that for the third characteristic - infection severity - these two new variants remain comparable to BA.5.
We should get a better idea tomorrow from the CDC's Nowcast how fast XBB.1.5 is spreading in the United States. Initial estimates - released 2 weeks ago - were rolled back last week (see COVID Nowcast: CDC Cuts Previous Estimate On XBB.1.5 By Roughly Half) after additional data was received.
