Omicron A Year Later: What Should We Know About the XBB.1.5 Subvariant?

By Francisco R. Velázquez, M.D., S.M., FCAP – Health Officer, Spokane Regional Health District

It was right around Thanksgiving 2021 when we first heard of a new SARS-CoV-2 variant of concern classified as B.1.1.529. Initially identified in South Africa, the new variant was assigned the next letter of the Greek alphabet, “O” (omicron). By the first week of December 2021, the presence of the new variant was confirmed in California. Now a year-plus later, and with over 300 subvariants of omicron identified, the newest member of the family, XBB.1.5, is circulating the world, identified in at least 29 countries, including here in the United States. Its presence has been increasing, accounting for roughly 1% of cases in the U.S. in early December, and as of Jan. 13, it is estimated to be 43% of all sequences in the U.S. In the northeast part of the country, over 70% of sequenced cases are XB.1.5. This is not unusual as one of the characteristics of the omicron sublineages has been the lack of total dominance by a single subvariant at a given point in time.

What do we know about this new subvariant? It is a descendant of the XBB omicron subvariant first identified in October. The “XBB” nomenclature points to a recombinant origin. Recombination, which is the process by which genetic material is exchanged in the viral genome during replication, is not uncommon in coronaviruses. In the XBB and XBB.1 scenario, it is the result of recombination of BA.2.75 and BJ.1, both members of the BA.2 family. Although XBB and XBB.1 were first identified in India, the origin of XBB.1.5 is unclear. It was first identified in the U.S., specifically in New York and Connecticut, thus raising the possibility that it originated in this country.

Biologically, this subvariant has demonstrated a higher level of immune evasion in various reported studies. This means it is more effective in terms of transmission as it evades post-infection and post-vaccine immunity in laboratory studies better that its predecessors. There is also some early evidence that it might be better at attaching to the human target receptor cells.

From a clinical perspective it does not seem to cause more severe disease for the average person than prior omicron subvariants. In recent months we saw its sibling, XBB, cause a significant increase in the total number of cases in places like Singapore but not a parallel increase in hospitalizations. One caveat is that the number of hospitalizations varies with immunizations status, age, pre-existing conditions and overall community activity. Although vaccines may not prevent disease transmission 100% of the time, COVID-19 vaccines have demonstrated to be very effective in preventing severe disease, hospitalizations and mortality. Recently published research suggests that while the XBB family is better at immune-evasion, people who have received an updated bivalent booster are more protected than those who have not.

What does this mean for all of us? First and foremost, we must remember that during the winter months many other respiratory viruses, like the flu, are more prevalent. We have seen the increased transmission with flu in all age groups as well as with RSV more specifically in children. This means that getting your flu and COVID-19 booster shots is very important. Following the basic precautions to protect yourself from respiratory viruses is critical: stay home if sick, contact your provider to get guidance about the appropriateness of testing or treatment, wash your hands, practice respiratory etiquette, and wear a mask in healthcare and public settings where it is difficult to distance yourself from others, especially if you’re at high risk of severe symptoms.

We have come a long way from the early days of the pandemic; however, the virus is still here and will be here for the foreseeable future. Let’s apply all the knowledge gained and all the resources that we now have, such as updated vaccines, so we can continue to manage its presence in the community and minimize its impact. We just experienced the most “normal” holiday season in the past three years. Let’s stay diligent so we can all continue to enjoy our great community. Happy New Year and best wishes for a healthy, happy and prosperous 2023.