New COVID-19 Subvariant XBB: Part of Omicron’s ‘New Class’

A new COVID-19 subvariant, XBB or Gryphon, has emerged and is gaining attention due to its ability to spread rapidly and evade immunity from previous COVID-19 infections or vaccinations. XBB is a hybrid version of two strains of the BA.2 form of Omicron and is part of a new class of Omicron variants that include BQ.1.1, BQ.1, BQ.1.3, BA.2.3.20, and XBB. XBB was first detected in India in August 2022 and has since been found in over 17 countries, including the US. A pre-print study from researchers in China suggests that XBB is the most antibody-evasive strain tested, far exceeding BA.5 and approaching the level of the strain that causes SARS. The study also suggests that antibody drugs like Evusheld and bebtelovimab may not be very effective against XBB.

Symptoms of XBB are similar to those of COVID-19 in general, including fever or chills, cough, shortness of breath, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose, nausea or vomiting, and diarrhea. XBB is highly contagious, and the Singapore Ministry of Health notes that the subvariant now accounts for 54% of COVID-19 cases in the country, up from 22% the week before.

There is currently no information on when XBB will peak, but the US continues to see BA.4.6 and BA.5 as the dominant variants. However, XBB is likely to spread to some degree in the US, and it is uncertain whether it or another related variant will become dominant. While the bivalent booster is likely to be protective against severe disease with XBB, it may not prevent infection. Vaccines still offer protection against severe disease, even with immune-evasive variants. Further research is needed to understand the implications of XBB on the ongoing COVID-19 pandemic.