#17,663
With a new, and largely enigmatic BA.2.86 variant spreading globally, researchers around the world are feverishly working to quantify its risks, including the Kei Seto Lab at the University of Tokyo. Over the past few years we've looked at a number of their assessments of emerging variants (see here, here, and here).
While their findings were telegraphed yesterday by the authors on Twitter/X, the full preprint was published overnight.
They find that BA.2.86 appears substantially less infectious (in vitro, using surrogate pseudoviruses) than currently circulating XBB strains and EG.5, but that it seems to make up for this deficit by ramping up its immune evasion; stating that `. . . results suggest that BA.2.86 is one of the most highly immune evasive variants ever.'
How all of this plays out in the real world, where BA.2.86 is in direct competition of literally dozens of other well-established variants, remains to be seen.Based on very limited data, they calculate its Effective Reproduction number (Re) to 1.29-fold greater than that of XBB.1.5 and comparable to or even greater than that of EG.5.1.
But between this report, and the UK's announcement earlier today of community transmission of BA.2.86 within the UK, this variant deserves our continued attention.
Abstract
In September 2023, the SARS-CoV-2 XBB descendants, such as XBB.1.5 and EG.5.1 (originally XBB.1.9.2.5.1), are predominantly circulating worldwide. Unexpectedly, however, a lineage distinct from XBB was identified and named BA.2.86 on August 14, 2023. Notably, BA.2.86 bears more than 30 mutations in the spike (S) protein when compared to XBB and the parental BA.2, and many of them are assumed to be associated with immune evasion.Although the number of reported cases is low (68 sequences have been reported as of 7 September 2023), BA.2.86 has been detected in several continents (Europe, North America and Africa), suggesting that this variant may be spreading silently worldwide.On 17 August 2023, the WHO designated BA.2.86 as a variant under monitoring. Here we show evidence suggesting that BA.2.86 potentially has greater fitness than current circulating XBB variants including EG.5.1. The pseudovirus assay showed that the infectivity of BA.2.86 was significantly lower than that of B.1.1 and EG.5.1, suggesting that the increased fitness of BA.2.86 is not due to the increased infectivity.We then performed a neutralization assay using XBB breakthrough infection sera to address whether BA.2.86 evades the antiviral effect of the humoral immunity induced XBB subvariants. The 50% neutralization titer of XBB BTI sera against BA.2.86 was significantly (1.4-fold) lower than those against EG.5.1. The sera obtained from individuals vaccinated with 3rd-dose monovalent, 4th-dose monovalent, 4th-dose BA.1 bivalent, and 4th-dose BA.5 bivalent mRNA vaccines exhibited very little or no antiviral effects against BA.2.86.Moreover, the three monoclonal antibodies (Bebtelovimab, Sotrovimab and Tixagevimab), which worked against the parental BA.2, did not exhibit antiviral effects against BA.2.86. These results suggest that BA.2.86 is one of the most highly immune evasive variants ever.