Despite intensive public health efforts to grind the COVID-19 pandemic to a halt, the recent emergence of the highly transmissible, extensively drug-resistant and profoundly immune system-evading XBB.1.5 SARS-CoV-2 subvariant is putting the global community on edge.
What is XBB.1.5?
In the naming convention for SARS-CoV-2 lineages, the prefix “X” denotes a pedigree that arose through genetic recombination between two or more subvariants.
The XBB lineage emerged following natural co-infection of a human host with two omicron subvariants, namely BA.2.10.1 and BA.2.75. It was first identified by public health authorities in India during summer 2022. XBB.1.5 is a direct descendent, or more accurately, the “fifth grandchild” of the original XBB subvariant.
Genetic lineage of COVID-19 subvariant XBB.1.5. (Sameer Elsayed), Author provided
How does XBB.1.5 differ from omicron?
XBB.1.5 is one of many omicron subvariants of concern that have appeared on the global pandemic scene since the onset of the first omicron wave in November 2021. In contrast to other descendants of the original omicron variant (known as B.1.1.529), XBB.1.5 is a mosaic subvariant that traces its roots to two omicron subvariant lineages.
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XBB.1.5 is arguably the most genetically rich and most transmissible SARS-CoV-2 omicron subvariant yet.
Where is XBB.1.5 prevalent?
According to the World Health Organization, XBB.1.5 is circulating in at least 38 countries, with the highest prevalence in the United States, where it accounts for approximately 43 per cent of COVID-19 cases nationwide. Within the U.S., there is wide geographic variation in the proportion of cases caused by XBB.1.5, ranging from seven per cent in the Midwest to over 70 per cent in New England.
XBB.1.5 has also been officially reported by governmental agencies in Australia, Canada, the European Union, Japan, Kuwait, Russia, Singapore, South Africa and the United Kingdom. Real-time surveillance data reveals that XBB.1.5 is rapidly spreading across the globe and will likely become the next dominant subvariant.
XBB.1.5 has also been detected in municipal wastewater systems in the United States, Europe and other places.
How likely is XBB.1.5 to cause serious illness?
There is limited data about the ability of XBB.1.5 to cause serious illness. According to the World Health Organization, XBB.1.5 does not have any specific mutations that make it any more dangerous than its ancestral subvariants.
Nonetheless, XBB.1.5 is perceived as being equally capable of causing serious illness in elderly and immunocompromised persons compared to previous omicron subvariants of concern.
Are current mRNA vaccines effective against XBB.1.5?
XBB.1.5 and XBB.1 are the omicron subvariants with the greatest …