What We Know About XBB.1.5, the New and Highly Contagious Omicron Subvariant


In just a month, the XBB.1.5 variant went from causing 1% to over 40% of new COVID-19 infections.

In just a month, the XBB.1.5 variant went from causing 1% to over 40% of new COVID-19 infections.

Omicron continues its reign as the dominant COVID-19 strain, and its new subvariant, XBB.1.5, is now most prevalent in the US.

As of the end of December 2022, Center for Disease Control and Prevention (CDC) genomic surveillance found XBB.1.5 was responsible for 40.5% of new COVID-19 infections. In the American Northeast, the CDC estimates XBB.1.5 is causing 75% of new infections.

Omicron BQ.1.1 and BQ.1, previously the reigning variants, are responsible for 26.9% and 18.3% of new cases, respectively.

XBB.1.5 swept across the country rapidly, as it made up only 1% of new infections a mere month ago. The subvariant appears to be 5 times more infectious than earlier Omicron strains, which were already 5 times more infectious than the original, wild-type COVID-19 virus.

Recent holiday gatherings, resistance to immune system antibodies, and an improved ability to bind tightly to the body’s ACE-2 receptors all likely contributed to the explosion of XBB.1.5 infections.

Although the World Health Organization (WHO) stated XBB.1.5 has a “growth advantage” above prior subvariants, there is currently no indication it will cause more severe or fatal disease. So far, symptoms of XBB.1.5 are believed to be consistent with earlier Omicron strains.

XBB.1.5 isn’t expected to cause more serious disease than prior COVID-19 variants, but it is still important to take all available precautions to avoid getting infected. The anticipated surge of XBB.1.5 infections will overburden the health system once again, and as we know, COVID-19 vaccines are less effective at preventing mild infection.

Fortunately, experts are confident COVID-19 vaccines will remain an effective prevention strategy. Individuals who have received an updated bivalent COVID-19 booster will benefit from even more effective protection.

Pfizer’s antiviral, Paxlovid, also significantly reduces the risk of severe or fatal disease progression.

This story will be updated as we learn more about the XBB.1.5 COVID-19 variant.

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