New variant modeling from the US Centers for Disease Control and Prevention (CDC) estimates emerging Omicron subvariants BQ.1 and BQ.1.1 now account for more than 10 percent of all infections in the United States. Scientists predict these rapidly spreading variants will drive a new wave of infections in the country over the coming months.
Late last week the CDC added several newly emerged SARS-CoV-2 variants to its weekly variant modeling report. Most significantly, two particular descendants of BA.5 were added to the model: BQ.1 and BQ.1.1.
Because of the slow pace of data collection across the United States, the CDC divides its variant surveillance report into two sections. The real empirical data, gathered by scores of commercial and academic laboratories around the country, usually trails real-time by two to three weeks.
Filling that gap is a prediction model developed by the CDC called Nowcast. The model offers projected growth estimates of certain circulating variants, and although Nowcast projections have proved relatively accurate in the past, it is important to remember they are speculative and not based on empirical data.
Important update of US genomic surveillance with noteworthy transition as BA.5 fades, BQ.1.1 quickly gains, along with other variants (BF.7, BA.2.75.2).https://t.co/jjl2AnwOWX pic.twitter.com/FuXdB42QuM
— Eric Topol (@EricTopol) October 14, 2022
According to a CDC spokesperson, BQ.1 and BQ.1.1 hadn't previously been added to the weekly variant report because empirical data had not shown them higher than 1% in prevalence around the country. Once the most recent collection data running up to the end of September revealed BQ.1 at 1.1% prevalence (and BQ.1.1 at 0.5%), the variants were added to the Nowcast report.
From this point the Nowcast modeling has estimated both variants to be spreading incredibly fast. As of October 15 they are projected to collectively account for over 11% of infections in the country.
These new subvariants were first detected less than two months ago, in late August, and designated with the BQ tag in early September. The detection came from a disparate community of variant trackers who are following the evolution of SARS-CoV-2 in granular detail.
Although these new BQ sublineages are suspected to already be driving new waves of infections in countries such as Germany and France, scientists tracking the virus's mutations suggest there are several independent lineages of Omicron that all seem to be converging on similar mutations. This phenomenon is known as convergent evolution, and it means different variants may become dominant and drive new waves in different countries, instead of one single variant taking over.
Looking at the data like this, we reduce the complexity behind numerous emerging variants into 4 buckets of increasing escape. This is not perfect as what's in a bucket is not totally the same, but it solves the problem of having to remember BQ.1.1, BA.2.75.2, XBB etc. 2/ pic.twitter.com/6KCwfbccN6
— Cornelius Roemer (@CorneliusRoemer) October 6, 2022
Viral evolution expert Cornelius Roemer suggests it is more helpful to group current subvariants by shared key mutations. From that perspective, Roemer classifies BQ.1 a Level 5 variant (carrying five key mutations from a list of about 20 genetic changes thought to generate significant immune escape properties).
Level 6 variants, according to Roemer, include BQ.1.1, BN.1, BM.1.1.1 and XBB. Interestingly, XBB is not currently listed in the CDC variant modeling, suggesting it is not at all prevalent in the United States. However, XBB is currently driving a significant new wave of infections in Singapore.
BQ.1* and XBB have different geographic foci
— Cornelius Roemer (@CorneliusRoemer) October 13, 2022
BQ.1* is mostly in Africa, Europe and North America
XBB in South (East) Asia
3 countries with similar levels worth watching for comparison and potential co-circulation are:
- Japan
- Australia
- South Koreahttps://t.co/YHzvfLgGOh 1/ pic.twitter.com/BiHKquBGxV
What isn't clear is where this is all heading. Tom Peacock, a virologist from Imperial College London, recently said the pace of mutations currently accumulating is akin to what would be expected from several years of influenza evolution, but here it has been "crammed into about three months."
Most experts are confident we will see a new wave of infections driven by these new variants over the coming months. But what isn't clear is whether these infections will translate into problematic levels of severe disease and hospitalizations.
Immunologist Menno van Helm says the virus won't necessarily always evolve in a direction leading to milder disease. Things certainly could become more challenging again in the future, but what he is confident of is that we won't completely return to that immunologically naive state we were in back in early 2020.
"It can get tricky again, and we can get a variant that could cause more issues that we have now," explained van Helm. "But I don't think we'll go back to 2020 where we're all naive and the prevalence of severe disease was much higher. I think even now treatment is much better. So once somebody gets severe disease, or somebody with underlying conditions gets infected, we are quick to add antivirals and add antibodies. So that will definitely help."
