Omicron subvariant XBB.1.5 jumps from 9.9% to 40.5% of U.S. COVID cases in two weeks

The COVID data tracker of the US Centers for Disease Control and Prevention (CDC) is showing a rapid increase in the proportion of the Omicron subvariant XBB.1.5 among circulating variants in the United States. This variant was fourth in prevalence for the week ending December 17th, accounting for 9.9% of circulating variants. During that same week, the most prevalent variants were BQ.1.1 (35.1%), BQ.1 (27.3%) and BA.5 (10.3%). By the week ending December 24th, XBB.1.5 had risen to third place (21.7%), behind BQ.1.1 (33.2%) and BQ.1 (24.1%).1 By December 31, XBB.1.5 had risen to 40.5% of circulating variants, followed by BQ.1.1 (26.9%), BQ.1 (18.3%) and BA.5 (3.7%).1 XBB is believed to be a recombinant of Omicron BA.2.10.1 and BA.2.75 sublineages.2 This suggests that the two variants exchanged genetic material to create a new version that carries aspects of both, which can occur when two different variants co-infect the same cell.3 Dr. Barbara Mahon, director of the CDC’s Coronavirus and Other Respiratory Viruses Division, reported to NBC News that a lot is still unknown about the XBB subvariant, including whether it is more contagious than other forms of Omicron. She also noted that COVID-19 hospitalizations have been increasing recently across the United States, but they do not appear to be rising more in the areas that have a higher prevalence of XBB.1.5.4 The XBB variant has also been the driving force behind an increase in cases in parts of Asia, including Singapore. Although some experts contend that it is more transmissible than other variants, it has not resulted in a surge in hospitalizations.5 However, experts are warning that this variant may also have a higher resistance to antibodies generated by vaccines or previous infection, or to therapeutic monoclonal antibodies, compared to previous strains.3 In mid-October 2022, the World Health Organization indicated that available preliminary laboratory-based evidence suggests that XBB is the most antibody-evasive SARS-CoV-2 variant identified to date.6 Dr. Isaac Bogoch, an infectious disease physician at University Health Network and epidemiologist at the University of Toronto, told NBC News that “It’s clear that there’s immune evasive properties of XBB. That’s been demonstrated both in laboratory studies and seen clinically in cases and hospitalizations. However, because of the high level of population immunity in the United States—through infection, vaccination or both—it is hoped that, even if cases start to rise significantly, there won’t be a dramatic spike in hospitalizations or deaths as seen in previous waves.”4 A small study recently published in the New England Journal of Medicine (online) found that the new bivalent (BA.4/BA.5) COVID-19 vaccine boosters from Moderna and Pfizer-BioNTech provide better protection against the XBB variant (and several other subvariants of Omicron) than the original or monovalent boosters.7 The key point to convey to the public is to get a booster shot with a bivalent vaccine to bolster the immune system against the newer subvariants. Getting the bivalent COVID booster is especially important for those over the age of 65, a high-risk group that has seen fairly low booster uptake in the United States.4 The Public Health Agency of Canada continues to monitor and identify COVID-19 variants in Canada, including sublineages of the Omicron variant; however, they are not yet seeing a trend similar to the United States. The Agency stated (via an email to CVV News) that “At this time, it is too early to tell if the XBB.1.5 variant is growing in Canada.”3 References 1. Centers for Disease Control and Prevention. COVID data tracker. Variant proportions. Weekly Nowcast estimates. https://covid.cdc.gov/covid-data-tracker/#variant-proportions (accessed January 3, 2023). 2. World Health Organization. TAG-VE statement on Omicron sublineages BQ.1 and XBB. October 27, 2022. https://www.who.int/news/item/27-10-2022-tag-ve-statement-on-omicron-sublineages-bq.1-and-xbb (accessed January 4, 2023). 3. Jones AM. What we know about Omicron subvariant XBB.1.5 spreading across the U.S. CTV News. Updated January 4, 2023. https://www.ctvnews.ca/health/coronavirus/too-early-to-tell-if-new-omicron-subvariant-xbb-1-5-spreading-across-u-s-is-growing-in-canada-phac-1.6216768 (accessed January 5, 2023). 4. Syal A. CDC reports a new strain of omicron taking over in the U.S. NBC News; December 31, 2022. https://www.nbcnews.com/health/health-news/xbb15-subvariant-cdc-reports-new-omicron-strain-taking-rcna63512 (accessed January 3, 2023). 5. Reuters staff. Omicron subvariant XBB jumps to 18% of US COVID cases: CDC. December 27, 2022. https://www.medscape.com/viewarticle/986094?src=WNL_trdalrt_pos1_ous_221229&uac=30288CV&impID=5043039 (accessed January 3, 2023). 6. World Health Organization. Weekly epidemiological update on COVID-19. October 19, 2022. Available at https://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19---19-october-2022 (accessed January 4, 2023). 7. Davis-Gardner ME, Lai L, Wali B, et al. Neutralization against BA.2.75.2, BQ.1.1, and XBB from mRNA bivalent booster. NEJM 2022; published online December 21, 2022. https://www.nejm.org/doi/full/10.1056/NEJMc2214293 (accessed January 3, 2023).

Omicron subvariant XBB.1.5 jumps from 9.9% to 40.5% of U.S. COVID cases in two weeks

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