Meet the New COVID-19 Subvariant, XBB

For the past several months, Omicron subvariant BA.4 and BA.5 have dominated COVID-19 cases in the U.S. But now, there’s a class of novel COVID subvariant on the rise and one in particular is attracting much of attention. It’s called XBB—or Gryphon—and there’s a chance it may overwhelm everything else out there.

XBB is getting a lot of buzz because it spreads fast—and seems to be able to evade immunity that people have built up from having a previous COVID-19 infection or getting the vaccine, says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine. Still, Dr. Schaffner notes, “it’s early days and we have a lot to learn.”

What is the XBB COVID variant?

XBB is one of the “new class” of Omicron variations that are spreading fast right now, says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York. That covers BQ.1.1, BQ.1, BQ.1.3, BA.2.3.20, and XBB, he claims.

“XBB is a hybrid version of two strains of the BA.2 form of Omicron,” explains Amesh A. Adalja, M.D., a senior scholar at the Johns Hopkins Center for Health Security. It’s currently “spreading efficiently in Singapore,” he adds.

XBB is expected to have the strongest capacity to resist antibody defences of these newly found COVID variants, according to a pre-print study from researchers in China. That report noted that the new strains of Omicron, and XBB in particular, “are the most antibody-evasive strain examined, significantly exceeding BA.5 and nearing SARS-CoV-1 level.” (SARS-CoV-1, in case you’re not familiar with it, is the strain of coronavirus that causes SARS, a respiratory virus that can cause serious disease.)

Meaning, the vaccine and having previously had COVID-19 are not thought to confer the same amount of protection against XBB as they have with earlier strains of COVID-19. Antibody medicines like Evusheld and bebtelovimab may also not be very effective against XBB, the pre-print study says.

“These mutations are evolving to circumvent protection,” Dr. Russo explains. The bivalent booster is “likely going to be protective against severe disease” with XBB, but will be “imperfect at avoiding infection,” Dr. Russo says.

Don’t panic, though. “When it comes to evasion of vaccine protection, it’s crucial to remember that vaccination protection is not all or none,” Dr. Adalja explains. “Even with immune-evasive variations, vaccine protection against what matters most—severe disease—remains intact.”

XBB variant symptoms

So far, symptoms of XBB seem to be comparable to what they’ve been with COVID-19 in general. According to the Centers for Disease Control and Prevention (CDC), those can include:

  •  Fever or chills
  • · Cough
  • · Shortness of breath or difficulty breathing
  • · Fatigue
  • · Muscle or body aches
  • · Headache
  • · New loss of taste or smell
  • · Sore throat
  • · Congestion or runny nose
  • · Nausea or vomiting
  • · Diarrhea

How contagious is the XBB subvariant?

Singapore’s Ministry of Health notes that the variation currently makes up 54% of COVID-19 cases in the country, up from 22% the week before.

Singapore’s Ministry of health believes that XBB is “at least as transmissible as currently circulating variants” but adds that “there is no evidence that XBB causes more severe illness.”

When will the XBB subvariant peak?

There are a lot of unknowns about XBB right now.

Other varieties are also begun to spread at the same time, Dr. Adalja says, and it’s unknown which will displace BA.4.6 and BA.5 in the U.S., if they will at all. “It’s likely to spread to some degree in the U.S. but unknown if it—or some other related variety such as BQ.1.1—will become dominant,” he says.

Dr. Schaffner believes there is “some anxiety” about XBB and fellow variations on the rise. “Watching what occurs over the next several weeks is important,” he says.

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