5 January 2023 Episode 304 XBB.1.5 a new threat?

Thu, 01/05/2023 - 13:05

Episode 304: XBB.1.5 or “Kraken”, the “new kid in town” made in US, is the fastest spreading subvariant since Omicron BA.1   

Dear colleagues,

First an addition to Ep 303: also colleague Kristof Decoster was contributing.  Sorry for the omission; Kristof: I really appreciated our inspiring e-mail exchange…

The present Episode is largely based again on input from Patrick Smits.

While all media attention is now focused on hypothetical potential new variants from China, the truth is that the next wave in Europe most probably will be fueled by an “American” variant.

It is a descendant from the XBB recombinant that caused a wave in Singapore last October, but now has gained some additional mutations, such that it is both more immune evasive and has a higher affinity for the ACE-2 receptor (hence more transmissible).  The crucial mutation is F486P.

We do not know yet whether it will be more pathogenic but  hospitalizations are rising in the Nord-East of US, where this variant is most prevalent. 

A more hypothetical question on whether it will increase long COVID (because of a broader range of infected cells) has also been asked.

I will not discuss all papers (Ep 304-1 to -6) in detail, just highlight some of the most illustrative figures and facts



The origin of XBB


Its rise and fall in Singapore






XBB.1.5 has a clear relative growth advantage over the former champion BQ..1.1




Spread: The first reported XBB.1.5 sample has been traced back to the 22nd of October in New York. A week later the variant was detected in Rhode Island and Washington state.

Scattered detections were then traced in India and Indonesia in early November

By mid Nov a number of European countries were picking up the new variant.



The current Nowcast model by CDC estimates XBB.1.5 cases have doubled in the US over the past week, and in the northeast of the country account for more than 75% of all confirmed cases.



This may be reflected in a rise of hospitalization, especially amongst 70+, but the relationship has not been proven


It is escaping immunity: low neutralizing activity of sera from RNA vaccinated and BA.5 super-infected individuals


A WT-BA.5 bivalent booster induced higher neut levels against XBB (XBB.1.5 not evaluated)



Yesterday, Maria Van Kerkhove, technical lead of WHO, expressed concerns on XBB.1.5 (Ep 304-6)

It has been detected in 29 countries so far but it could be even more widespread, Van Kerkhove said. Tracking Covid variants has become difficult as genomic sequencing declines across the world, she said.

The WHO doesn’t have any data yet on the severity of XBB.1.5, but there’s no indication at the moment that it makes people sicker than previous versions of omicron, Van Kerkhove said. The WHO’s advisory group that tracks Covid variants is conducting a risk assessment on XBB.1.5 that it will publish in the coming days, she said.



For sure the new variant is spreading, but will it cause a new “overload” in our hospitals, which are already stressed by the flu epidemic? . 

Factor 1: Vaccination

  • On one hand, we are in a better position than US, because we have a higher and more recent booster rate than US, especially in the elderly.
  • BUT the bivalent vaccine used in Europe (WT-BA.1) may be less protective against advanced variants than the WT-BA.5 used in US.

Factor 2 Innate immunity

  • Theoretically, the circulating FLU and other viruses may increase our resistance to new viruses, by activating type 1 IFN and other immune factors.
  • BUT it is well known that this protective mechanisms wanes with ages and that dual viral infections (e.g. Flu + Corona) are more common in the elderly and have a bad prognosis.   

Factor 3: Non-pharmacological interventions: avoiding crowds, wearing face masks, ventilation… have largely been abandoned, even by elderly…. Unfortunately.


To be continued for sure….

Best wishes,