What we know about Omicron subvariant XBB.1.5 spreading across the US

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Thursday, January 5, 2023
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NEW YORK CITY -- A new Omicron subvariant is now driving COVID-19 outbreaks in the U.S.

At the beginning of December, Omicron sub-variant XBB.1.5 made up just 1.3% of all COVID-19 cases in the U.S. By the end of that same month, XBB.1.5 was responsible for 40% of cases in the U.S, according to data from the U.S. Centers for Disease Control and Prevention (CDC).

The percentage of cases attributed to XBB.1.5 doubled in the span of one week at the end of December, from 21.7% to 40.5%, according to the CDC.

This variant's sudden growth is causing concern among health experts, who warn that this variant may have a higher resistance to antibodies than previous strains.

The Public Health Agency of Canada (PHAC) told CTVNews.ca in an email that they are continuing to monitor and identify COVID-19 variants in Canada, including sublineages of the Omicron variant, but that we aren't seeing a trend similar to the U.S. at the moment.

"At this time, it is too early to tell if the XBB.1.5 variant is growing in Canada," the agency stated.

"PHAC scientists continue to monitor cases in Canada and track developments internationally."

What is XBB.1.5 and when did it first show up?

XBB.1.5 is the latest in a long string of descendants of the Omicron variant of SARS-CoV-2, the virus that causes COVID-19.

As the virus evolves, it develops new mutations that subtly change its structure and plan of attack - the variants and subvariants that catch on are the ones that have developed mutations that allow them to better infect our cells or evade antibodies. Since Omicron emerged, its offshoots have dominated COVID-19 infections across the globe.

It's currently unclear where XBB.1.5 first emerged, but scientists began to warn about a new Omicron lineage in the fall.

In a statement on Oct 27, the World Health Organization (WHO) explained that XBB and its sublineages were actually a recombinant of the Omicron BA.2.10.1 and BA.2.75 subvariants. This means that the two variants exchanged genetic material to create a new version that carries aspects of both, something that can occur when two different variants co-infect the same cell.

As of Oct. 17, the WHO stated that XBB had been reported in 26 countries. While XBB and XBB.1 are believed to have been first identified in India before spreading across regions of Asia such as Singapore, XBB.1.5 was first detected in the U.S. in New York and Connecticut in late October, according to the Global Initiative on Sharing Avian Influenza Data, an international organization that aims to track and sequence variants.

According to CDC data, XBB.1.5 started spreading quickly across the U.S. in December. In the northeast, the variant has taken over: XBB.1.5 makes up 72% of all cases in New York State and New Jersey, and 75% in New England, per the CDC.

What do we know about it?

Not much is known about XBB.1.5 in particular yet, but early research has suggested that XBB and its sublineages are significantly better at evading antibodies generated by vaccines or previous infection.

"Available preliminary laboratory-based evidence suggests that XBB is the most antibody-evasive SARS-CoV-2 variant identified to date," the WHO stated in its Oct. 19th epidemiological update.

A study published in the peer-reviewed journal Cell in mid-December found that the BQ and XBB Omicron subvariants were much better at evading antibodies. While these subvariants carried the same trait that allowed Omicron to better attach to cell receptors to infect human cells, monoclonal antibodies capable of neutralizing the original Omicron variant largely weren't able to stop these newer variants, the study found.

The results of another small study published Dec 21 in the peer-reviewed New England Journal of Medicine suggest that mRNA booster shots may be much less effective at neutralizing XBB and BQ.1.1. In one test looking at the serum samples of participants who received a bivalent booster shot, the level of neutralization was 12 to 26 times lower in XBB and BQ.1.1 compared to the original 2020 strain, and "neutralizing activity was lowest against the XBB subvariant". However, authors cautioned that their study was limited by a very small sample size of around 35 participants.

Is it more dangerous?

If XBB.1.5 is more transmissible and can evade antibodies easier than other variants, it could be more dangerous in terms of number of infections, since a virus that infects more people has more chances to inflict harm or even death.

The WHO noted in its October statement that the data did not suggest that XBB and its sublineages were causing more severe disease.

However, it added that the risk of reinfection appears to be higher with XBB than with other circulating Omicron variants.

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