COVID: What we know about Omicron’s XBB.1.5 sub-variant

A new Omicron sub-variant is now driving the COVID-19 outbreak in the US

At the beginning of December, the XBB.1.5 sub-variant of Omicron accounted for only 1.3% of all COVID-19 cases in the United States. By the end of that month, XBB.1.5 was responsible for 40% of cases in the United States, according to data from the US Centers for Disease Control and Prevention (CDC).

According to the CDC, the proportion of cases attributed to XBB.1.5 doubled over a one-week period in late December, from 21.7% to 40.5%.

The sudden growth of this variant is worrying medical experts, who warn that the variant may be more resistant to antibodies than previous strains.

The Public Health Agency of Canada (PHAC) told in an email that it is continuing to monitor and identify COVID-19 variants in Canada, including sublines of the Omicron variant, but they are I don’t see the same trend as the US at the moment.

“At this point, it is too early to know if the XBB.1.5 variant is in development in Canada,” the agency said.

“PHAC scientists continue to monitor cases in Canada and monitor developments internationally.”


XBB.1.5 is the latest in a long line 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 alter its structure and attack plan – catch-up variants and sub-variants are those that have evolved mutations for allow them to better infect our cells or evade antibodies. Since Omicron appeared, its affiliates have dominated COVID-19 infections globally.

It is currently unclear where XBB.1.5 first appeared, but scientists began warning of a new strain of Omicron in the fall.

In a statement on October 27, the World Health Organization (WHO) explained that XBB and its sublines are actually a recombination of the Omicron sub-variants BA.2.10.1 and BA .2.75. This means that the two variants have exchanged genetic material to create a new version that has characteristics of both, something that can happen when two different variants infect the same cell.

As of October 17, WHO states that XBB has been reported in 26 countries. While XBB and XBB.1 are believed to have first been identified in India before spreading throughout Asian regions such as Singapore, XBB.1.5 was first detected in the United States in New York and Connecticut. in late October, according to the Global Initiative for Avian Influenza Data Sharing, an international organization that aims to track and sequence variants.

According to CDC data, XBB.1.5 began spreading rapidly across the US in December. In the northeast, the variant took over: XBB.1.5 accounted for 72% of all cases in New York State and New York. Jersey, and 75% in New England, according to the CDC.


Not much is known specifically about XBB.1.5, but early research has suggested that XBB and its sublines are significantly better at avoiding vaccine-generated antibodies or previous infection.

“Preliminary laboratory-based evidence available suggests that XBB is the most antibody-resistant SARS-CoV-2 variant identified to date,” the WHO said in its October 19 epidemiological update.

A study published in the journal Cell in mid-December found that the BQ and XBB Omicron sub-variants were much better at avoiding antibodies. Although these sub-variants carry the same trait that allows Omicrons to better bind to cellular receptors to infect human cells, monoclonal antibodies are capable of neutralizing the original Omicron variant for the most part. could not prevent these newer variants, the study found.

The results of another small study published December 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 a trial that looked at serum samples from participants who had received a booster dose of bivalent, the level of neutralization in XBB and BQ.1.1 was 12 to 26 times lower than in the 2020 baseline and “ neutralizing activity was the lowest compared with the XBB sub-variant”. However, the authors caution that their study was limited by a very small sample size of about 35 participants.


If XBB.1.5 is more transmissible and can evade antibodies more easily than other variants, it could be more dangerous in terms of number of infections, as the virus infects more people with a greater chance harm or even death.

The WHO noted in its October statement that the data do not suggest that XBB and its subtypes cause more serious disease.

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


XBB and its sublines have been detected in Canada, but presently in very small numbers. According to Public Health Ontario’s risk assessment in early November, there were six cases of XBB and five cases of XBB.1 in Ontario between September 25 and October 22.

According to the most recent PHAC data, BA.5 and its sublines remained the most dominant strain across Canada as of mid-December, accounting for 92.5% of the samples analyzed at that time.

Detailed analysis of variants discovered in Canada weekly through genome sequencing lists XBB.1.5 accounting for approximately 0.6% of samples analyzed during the week of 11 December.

In the same week, the sub-variant BQ.1.1, counted by PHAC as BA.5, accounted for 30.7% of the sequenced samples.


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