The XBB.1.5 variant is the most contagious discovered to date, but is it also a champion of immune escape? A prepublication delivers the first elements of an answer.
XBB.1.5, or the “Kraken” as a Canadian biology professor dubbed it who would like to see SARS-CoV-2 variants renamed after monsters from Greek mythology, is highly contagious but does it escape our immune defenses? For each new variant detected, scientists must answer this crucial public health question.
Escape from the “Kraken” variant antibodies
The data available for XBB.1.5 is still very incomplete. A preprint on BioRvix tackled this question by studying the cellular and humoral immune response of 30 volunteers who received a booster dose of a bivalent RNA vaccine from Pfizer or Moderna, designed to fight Omicron variants. Their serum was collected and brought into contact with virus-like particles mimicking the XBB.1.5 variant to test the neutralizing properties of the antibodies and, in a second test, the effectiveness of the T cells.
Unsurprisingly, XBB.1.5 escapes neutralizing antibodies, but in similar proportions to what was observed for XBB.1. The F486P mutation located in protein S makes it highly contagious but does not increase its immune escape. The cross-reactive T lymphocytes remain always active against XBB.1.5. The preprint also points out that the booster dose is only effective for three months, after which the amounts of neutralizing antibodies fall back to their pre-booster level. Even if its effectiveness decreases quickly, the vaccine booster dose is the most effective and safe way to protect against the appearance of new variants of SARS-CoV-2.
