For the 3rd month running XBB.1.5 remains firmly in control across the United States (see chart above), but in India and a few other countries, a new up-and-coming XBB.1.16 variant is said to be spreading rapidly.
A few days ago Sato Lab in Japan released their own (preprint) analysis of XBB.1.16, which finds that this new variant to be even more transmissible, and immune evading, than its predecessors. So far, however, there is no indication that XBB.1.16 produces any more severe illness than previous Omicron variants.
Since Omicron variants have a history of remaining dominant for only 3 or 4 months, it is likely that XBB.1.5 will eventually be replaced, and right now XBB.1.16 appears to be leading candidate.
Virological characteristics of the SARS-CoV-2 Omicron XBB.1.16 variant
Daichi Yamasoba, Keiya Uriu, Arnon Plianchaisuk, Yusuke Kosugi, Lin Pan, Jiri Zahradnik, The Genotype to Phenotype Japan (G2P-Japan) Consortium, Jumpei Ito, Kei Sato
At the end of March 2023, XBB.1.16, a SARS-CoV-2 omicron XBB subvariant, emerged and was detected in various countries. Compared to XBB.1.5, XBB.1.16 has two substitutions in the S protein: E180V is in the N-terminal domain, and T478R in the receptor-binding domain (RBD).We first show that XBB.1.16 had an effective reproductive number (Re) that was 1.27- and 1.17-fold higher than the parental XBB.1 and XBB.1.5, respectively, suggesting that XBB.1.16 will spread worldwide in the near future. In fact, the WHO classified XBB.1.16 as a variant under monitoring on March 30, 2023.Neutralization assays demonstrated the robust resistance of XBB.1.16 to breakthrough infection sera of BA.2 (18-fold versus B.1.1) and BA.5 (37-fold versus B.1.1). We then used six clinically-available monoclonal antibodies and showed that only sotrovimab exhibits antiviral activity against XBB subvariants, including XBB.1.16. Our results suggest that, similar to XBB.1 and XBB.1.5, XBB.1.16 is robustly resistant to a variety of anti-SARS-CoV-2 antibodies.Our multiscale investigations suggest that XBB.1.16 has a greater growth advantage in the human population compared to XBB.1 and XBB.1.5, while the ability of XBB.1.16 to exhibit profound immune evasion is comparable to XBB.1 and XBB.1.5.The increased fitness of XBB.1.16 may be due to (1) different antigenicity than XBB.1.5; and/or (2) the mutations in the non-S viral protein(s) that may contribute to increased viral growth efficiency.
Altogether, our data suggest that XBB.1.16 has a greater growth advantage in the human population compared to XBB.1 and XBB.1.5, while the ability of XBB.1.16 to exhibit profound immune evasion is comparable to XBB.1 and XBB.1.5. The increased fitness of XBB.1.16 may be due to (1) different antigenicity from XBB.1.5; and/or (2) the mutations in the non-S viral protein(s) that may contribute to increased viral growth efficiency.