More immunoevasive and transmissible, but not more serious. The evidence on the variant of Sars-CoV-2 baptized Kraken on social media, i.e. Omicron XBB.1.5, is strengthened. And these are the qualities that now appear to be more accurately looming, according to the World Health Organization’s (WHO) latest assessment of the risk posed by this mutant, reported in its weekly Covid update. “There is evidence of an increased risk of transmission and immune escape. This evidence is of moderate strength.” Based on its genetic characteristics and growth rate estimates, it “is likely to contribute to the increased incidence of ‘Covid’ cases globally.” From reports from several countries, “no early signs of increased severity have been observed.”
But, it is pointed out, “the number of cases associated with XBB.1.5 is still low and therefore the severity cannot yet be assessed with confidence”. Taken together, the WHO assessment concludes, the available information suggests that Kraken “appears to have no additional public health risks compared to other Omicron descendant lineages.” The new UN health agency analysis comes after the latest expert meeting of the WHO Technical Advisory Group on the Evolution of the Virus (TAG-Ve), which was held on 23 January. WHO has also revised the level of confidence in the risk assessment, which now rises from low (January 11) to moderate (January 25), as the analysis relied on additional reports from countries on the prevalence and benefit of Kraken growth and additional laboratory studies.
XBB.1.5 is the descendant lineage of XBB, recombinant of two BA.2 descendant lineages. Most of his sequences deposited in the database come from the USA. From October 2022 to January 23, 2023, 8,931 Kraken sequences were reported from 54 countries, 75% of which were from the United States. The countries with a prevalence above 1% are the United Kingdom (9.9%), Canada (3%), Denmark (2%), Germany (1.5%), Ireland (1.3%) and Austria (1.3%).
WHO and TAG-Ve recommend Member States prioritize studies to overcome the uncertainties related to growth advantage, antibody escape and severity of XBB.1.5. Overall the agency is currently closely monitoring four Omicron descendant lineages: BF.7, the BQ.1 group (and BQ.1.1 Cerberus), BA.2.75 Centaurus (including its ‘children’ BA.2.75.2 and CH.1.1) and the XBB family (including Kraken XBB.1.5). The risk analysis is disseminated precisely for the latter.
Compared to early January assessments, WHO notes, “more countries have reported an increase in the prevalence of XBB.1.5. The variant has a growth advantage, based on reports from the US, UK and the European Center for Prevention and disease control (ECDC). Preliminary laboratory studies on antibody escape “indicate that XBB.1.5 has greater immunoevasiveness than other Omicrons prior to XBB in vaccinated with three doses of mRNA vaccine, even if neutralization was restored by a bivalent booster. These results point to confirmed in vaccine efficacy studies.
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