This article was originally published on Oct. 30, 2022, but has been updated with recent information.
Viruses change constantly as they circulate through a population, and these changes can sometimes create completely new variations of a virus. This is certainly true of SARS-CoV-2.
Since its initial appearance around three years ago, the virus that causes COVID-19 has splintered into several separate strains, including Alpha, Beta, Delta and Omicron. And these strains have only continued to separate into their own subvariants at an astonishing speed.
One of these subvariants, BA.5, prevailed throughout the summer season in 2022, contributing to the plurality of coronavirus cases in the U.S. throughout that time. That said, several newer strains have taken over since then, transforming into the country's top coronavirus culprits.
This is what you'll want to know about several of these new subvariants, including BQ.1, BQ.1.1 and XBB.1.5.
BQ.1 and BQ.1.1
In the year-or-so since scientists first found the Omicron variation of the virus, this variant has split into an assortment of over 500 separate subvariants, including this summer's BA.5 strain.
Overall, it's thought that the symptoms of the original variant and subsequent subvariants aren't any more serious than those associated with the initial SARS-CoV-2 virus (and are sometimes seen as more mild). That said, the science is nascent, and scientists still consider these viral varietals a concern, since they are all remarkably resistant to the internal immunities from previous infections and vaccinations.
Specialists say that this resistance allowed BA.5 to spread widely throughout the U.S., and at a whirlwind speed, some several weeks ago. But according to the Centers for Disease Control and Prevention, the strain is now subsiding, accounting for fewer than 3 percent of the current coronavirus cases in the country.
And taking its place as the most common (and most concerning) strains of SARS-CoV-2 are several new subvariants from the same family.
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Take, for instance, the two Omicron subvariants known as BQ.1 and BQ.1.1. Initially identified in July 2022, both strains are direct descendants of BA.5. Now, the combination of the two is causing approximately 45 percent of all coronavirus cases in the U.S., making them two of the most common strains in the country.
Though the BQ.1 and BQ.1.1 subvariants aren’t associated with any more severe symptoms than BA.5 or any other older variation of the SARS-CoV-2 virus, it's clear that the two are causing trouble and could continue to cause trouble throughout the upcoming weeks. In fact, preliminary studies show that an assortment of mutations to both BQ.1 and BQ.1.1 boost their ability to avoid antibodies to a stunning seven times above BA.5’s.
The ‘Kraken,’ XBB.1.5
BQ.1 and BQ.1.1 aren't the only Omicron subvariants to worry about, nor are they the only Omicron subvariants armed with an arsenal of mutations for sidestepping internal immunities. Some up-and-coming variations of the virus, including varietals from the XBB family, for instance, are not only as skilled as BQ.1 and BQ.1.1 at skirting around antibodies, but are also substantially better at invading cells, all thanks to their adaptations.
These XBB varietals, including XBB.1 and its direct descendant XBB.1.5, are amalgamations of several older subvariants of Omicron, though that doesn’t mean that they are any weaker than the Omicron strains that are wholly new. While XBB.1 appeared in the U.S. in September, XBB.1.5 arose in October and is already the top variant in terms of transmissibility, producing 43 percent of the country’s coronavirus cases.
Since the start of January, XBB.1.5 has supplanted both BQ.1 and BQ.1.1 as the top subvariant in the U.S. (though the combination of the two still sits slightly above the new strain). And that’s because XBB.1.5, despite sharing a similar array of adaptations with the older Omicron strains, also boasts several special traits, making it all the more transmissible.
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The surfaces of all Omicron subvariants are covered in a mutated, misshapen form of spike protein, which informs the way that these subvariants interact with the outside world. In particular, these mutated spike proteins allow Omicron strains to slip past antibodies better than all previous versions of the virus, and the same is still true for XBB.1.5.
It's these mutations that make Omicron subvariants so transmissible, though this increase in transmissibility tends to come at a cost, making it more challenging for these viruses to attach to the cells that they strive to infect. Yet preliminary papers on XBB.1.5 paint another picture, suggesting that the strain carries several additional mutations that allow it to cling tightly to cells once again.
Ultimately, whether BQ.1, BQ.1.1 or XBB.1.5, scientists say that these strains are all playing a part in increasing infections. Cases are climbing across the country, with weekly counts at around 410,000, and could continue to surge as the winter season stumbles on. As such, these scientists advise that people continue to stay cautious and continue to acquire their vaccinations to reduce their risk of coronavirus.
In fact, some studies — though not all — suggest that because BQ and XBB both descend from Omicron, the bivalent boosters that specifically target that family of viruses family could confer additional protection against BQ.1, BQ.1.1 and XBB.1.5, despite their shared skill at dodging antibodies.
The Bonus Boston Variant
The strains described above developed naturally, as an unavoidable by-product of viral reproduction and replication. That said, some scientists are also creating separate, artificial strains as a way to study SARS-CoV-2. Though these artificial variations aren't varietals that we necessarily need to worry about, one particular artificial variation recently received some attention this fall for its seemingly abnormal mortality rates.
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After noticing that Omicron strains seem to share similar spike protein mutations and similar mild symptoms, Boston University scientists decided to develop their own unique variant of the virus. This strain combined the spike protein mutations typical of Omicron variants with other traits typical of older, non-Omicron variants of SARS-CoV-2, all in an attempt to determine whether the structure of the spike protein is what determines the severity of the disease after an infection does occur.
The scientists tested their strain on mice. While their artificial varietal killed a shocking 80 percent of the mice on which it was tested, the older, non-Omicron variants of SARS-CoV-2 without altered spike proteins were much more deadly, killing 100 percent of the test organisms.
The mortality rate of the scientists' strain was relatively similar to the original SARS-CoV-2 variants without altered spike proteins. Therefore, the researchers concluded that the spike protein mutations do not determine the seriousness of COVID-19 symptoms whenever the disease does develop.
Ultimately, while they couldn't pinpoint what determines symptom severity, the silver lining is that the Boston University variant isn't in the mix of increasingly widespread strains like BQ.1, BQ.1.1 and XBB.1.5.