A new subvariant of the novel-coronavirus called XBB dramatically announced itself earlier this week, in Singapore. New COVID-19 cases more than doubled in a day, from 4,700 on Monday to 11,700 on Tuesday—and XBB is almost certainly why. The same subvariant just appeared in Hong Kong, too.
A highly mutated descendant of the Omicron variant of the SARS-CoV-2 virus that drove a record wave of infections starting around a year ago, XBB is in many ways the worst form of the virus so far. It’s more contagious than any previous variant or subvariant. It also evades the antibodies from monoclonal therapies, potentially rendering a whole category of drugs ineffective as COVID treatments.
“It is likely the most immune-evasive and poses problems for current monoclonal antibody-based treatments and prevention strategy,” Amesh Adalja, a public-health expert at the Johns Hopkins Center for Health Security, told The Daily Beast.
That’s the bad news. The good news is that the new “bivalent” vaccine boosters from Pfizer and Moderna seem to work just fine against XBB, even though the original vaccines are less effective against XBB. They won’t prevent all infections and reinfections, but they should significantly reduce the chance of severe infection potentially leading to hospitalization or death. “Even with immune-evasive variants, vaccine protection against what matters most—severe disease—remains intact,” Adalja said.
As the novel-coronavirus evolves to become more contagious and more resistant to certain types of drugs, keeping current on your boosters is “the most impactful thing you can do in preparation for what might come,” Peter Hotez, an expert in vaccine development at Baylor College, told The Daily Beast.
Scientists first identified XBB in August. It’s one of several major subvariants that have evolved from the basic Omicron variant, piling on more and more mutations on key parts of the virus—especially the spike protein, the part of the virus that helps it grab onto and infect our cells.
XBB has at least seven new mutations along the spike. Mutations that, taken together, make the subvariant harder for our immune systems to recognize—and thus more likely to evade our antibodies and enter our cells to cause infection.
This accumulation of mutations isn’t surprising. Changes along the spike protein have characterized most of the major new variants and subvariants of SARS-CoV-2 as the pandemic grinds toward its fourth year.
What is surprising is how much competition XBB has as it fights to become the next dominant form of the novel-coronavirus. Several other Omicron subvariants are also in circulation. All of them are highly evolved. Many of them actually share a subset of key mutations, especially on the spike.
So while XBB appears to be gaining traction in Asia, a close cousin of XBB called BQ.1.1 is spreading fast in Europe and some U.S. states. There are others in contention, too, including BA.2.75.2. Hotez calls these viral cousins the “Scrabble” subvariants, a nod to the classic word game and the jumble of scientific designations of closely related viruses.
The Scrabble variants are indicative of what scientists call “convergent evolution.” That is, separate viral sublineages that are picking up more and more of the same mutations. It’s as though Omicron’s children are all separately learning how to be a better virus than their parent, and becoming more like each other in the process.
Immune-escape is the common quality. At least two of the Scrabble subvariants—XBB and BQ.1.1—are pretty much unrecognizable to existing antibody therapies and somewhat less recognizable to the antibodies produced by the prime doses of the leading messenger-RNA vaccines.
In evading some of our therapies and, to a lesser extent, our original vaccines, XBB and its cousins are showing us where the novel-coronavirus is heading, genetically speaking. The current surge in infections in places like Singapore is a preview of a potential global surge, this coming winter or spring, as XBB or one of its relatives becomes dominant everywhere.
It’s possible to mitigate the worst outcomes. Natural antibodies from past infection are still the best and most durable antibodies. They don’t last forever. But while they do last—a few months or potentially a whole year—the chance of catching a bad case of COVID is pretty low.
So if you had an earlier form of Omicron—say, during the wave of infections that started last Thanksgiving and peaked around February—you might still have good antibodies for a few months. More than enough time to reinforce those fading natural antibodies with a dose of the latest mRNA boosters.
Pfizer and Moderna formulated these new boosters to include some genetic instructions specifically for attacking the BA.5 subvariant of Omicron, which is still the dominant form of SARS-CoV-2 but is disappearing fast as XBB and the other Scrabble subvariants outcompete it.
The bivalent boosters should work pretty well against forms of the virus that are closely related to BA.5, including the Scrabbles. “That is because one of the two components [in the boosters] induces an immune response to BA.5, and most of the new Scrabble variants look more BA.5 like than [the] original China lineage,” Hotez told The Daily Beast.
The implication, of course, is that we’re eventually going to need another new booster in order to keep pace with the fast-evolving virus. Sure, the bivalent boosters work against BA.5 and BA.5’s immediate descendants. But what about the next generation of Omicron subvariants, the one after XBB and its cousins?
More and more health officials are coming around to the idea of an annual COVID booster. U.S. president Joe Biden even endorsed the idea in a statement last month. “As the virus continues to change, we will now be able to update our vaccines annually to target the dominant variant,” Biden said. “Just like your annual flu shot, you should get it sometime between Labor Day and Halloween.”
But one booster a year might not be enough if, as some epidemiologists fear, natural antibodies fade faster and the novel-coronavirus mutates at an accelerating rate. One concern, if it turns out we need twice-a-year new boosters, is whether industry can develop fresh jabs fast enough and health agencies can swiftly approve them.
There’s an even bigger question, however. “The more important factor is just having folks get a more recent booster,” James Lawler, an infectious disease expert at the University of Nebraska Medical Center, told The Daily Beast.
Even if a new booster is available every six months or so, will enough people get it to make a difference in the overall rates of severe illness and death? Booster uptake is declining globally, but especially in the United States, where just 10 percent of people have gotten the bivalent booster since federal regulators approved them in August.
XBB is a nasty little subvariant. But it’s not the final word on COVID. The novel-coronavirus will keep mutating, and finding new ways to evade our antibodies, whether or not many people are paying attention.
The virus isn’t done with us. Which means we can’t be done with it. Get boosted. And be prepared to get boosted again in 2023.