Pre-Existing Population Immunity and severe acute respiratory syndrome coronavirus 2 Variant Establishment and Dominance Dynamics in the United States: An Ecological Study.

We conducted an ecological analysis of the dynamics of Delta and Omicron establishment and dominance in US states. Omicron became the dominant circulating variant later in states with higher population-level immunity. By contrast, population immunity did not impact the maximum rate of takeover by Delta or Omicron from prior variants.

The SARS-CoV-2 Delta-Omicron Recombinant Lineage (XD) Exhibits Immune-Escape Properties Similar to the Omicron (BA.1) Variant.

Recently, a recombinant SARS-CoV-2 lineage, XD, emerged that harbors a spike gene that is largely derived from the Omicron variant BA.1 in the genetic background of the Delta variant. This finding raised concerns that the recombinant virus might exhibit altered biological properties as compared to the parental viruses and might pose an elevated threat to human health. Here, using pseudotyped particles, we show that ACE2 binding and cell tropism of XD mimics that of BA.1. Further, XD and BA.1 displayed comparable sensitivity to neutralization by antibodies induced upon vaccination with BNT162b2/Comirnaty (BNT) or BNT vaccination followed by breakthrough infection. Our findings reveal important biological commonalities between XD and Omicron BA.1 host cell entry and its inhibition by antibodies.

Potential intervariant and intravariant recombination of Delta and Omicron variants.

Among numerous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concerns, Omicron is more infectious and immune-escaping, while Delta is more pathogenic. Here, we provide evidence for both intervariant and intravariant recombination of the rapidly evolving new SARS-CoV-2 genomes, including XD/XE/XF and BA.3, raising concerns of potential more infectious, immune-escaping, and disease-causing Omicron and Delta-Omicron variants.