In a paper published on Jan. 3rd on the preprint platform bioRxiv, Yunlong Cao’s research team revealed the reasons for the increased transmission of the Omicron XBB.1.5 strain.
XBB.1.5 is a subvariant of the recombinant mutant strain XBB.
It is currently spreading rapidly in the United States.
Compared to XBB.1, BQ.1.1, and other strains under the XBB spectrum, XBB.1.5 has an additional mutation site (Ser486Pro) on the stinger protein.
Researchers collected recovery plasma samples from patients who developed breakthrough infection with BA.1, BA.5 or BF.7 after 3 doses of Coxin vaccine and assessed the 50% neutralization titer (NT50) of plasma against XBB.1 and XBB.1.5.
The study showed that compared to B.1, plasma samples from BA.5 breakthrough infections had 44-fold and 39-fold lower NT50 against XBB.1 and XBB.1.5, respectively, and plasma samples from BF.7 breakthrough infections had 31-fold and 27-fold lower NT50, respectively.
This also showed that XBB.1 and XBB.1.5 could significantly escape the neutralization of antibodies in plasma, with XBB.1.5 having a slightly weaker immune escape than XBB.1.
They also found that XBB.1.5 had a stronger affinity for hACE2 than the BQ.1.1 and XBB/XBB.1 strains.
In addition, the antibodies Evusheld and Bebtelovimab were unable to neutralize XBB.1/XBB.1.5, and Sotrovimab was less neutralizing, although SA55 remained effective.
It was shown that the increased affinity of XBB.1.5 and receptor binding does result in a greater infection advantage.