CDC Nowcast - May 24th
#16,787
Although cases around the world are increasingly under-reported due to the reductions in lab testing, it is clear that the United States is seeing a resurgence of COVID due to the Omicron BA.2.12.1 variant, which has slowly been gaining ground on - and recently surpassed - BA.2 (see CDC map above).
Elsewhere in the world, we are seeing the dominance of BA.2 eroded by the rise of new Omicron variants, particularly BA.4 and BA.5.
While it isn't known whether these three variants produce any greater severity of illness than BA.2, anecdotal reports suggest reinfection following BA.1 or BA.2 infection is common, and vaccine protection against symptomatic infection appears even lower than with earlier Omicron variants.
Unless a new, even more biologically `fit' COVID virus emerges in the near-term, it appears that our pandemic's immediate future will be determined by the global spread, and success, of BA.2.12.1, BA.4, and BA.5.
Researchers around the world are using a variety of techniques to quantify the risks of these emerging variants, including the Kei Seto Lab at the University of Tokyo. Last February, when BA.1.1 was still dominant, we looked at the Seto Lab's analysis of the COVID heir apparent (see Preprint: Virological characteristics of SARS-CoV-2 BA.2 variant).
Yesterday they published a new preprint, this time on BA.2.12.1, BA.4, and BA.5
Since isolates of these substrains were not readily available, they substituted lab-created chimeric recombinant SARS-CoV-2 viruses to approximate each subvariant, in order to conduct animal experiments. While infected hamsters (or mice, or ferrets) can provide valuable information, they aren't an exact analog for humans, and so that data must be viewed with a certain degree of caution.
With those caveats in mind, we have the link, abstract, and some excerpts from the Sato Lab's preprint.
Virological characteristics of the novel SARS-CoV-2 Omicron variants including BA.2.12.1, BA.4 and BA.5Izumi Kimura, Daichi Yamasoba, Tomokazu Tamura, Naganori Nao, Yoshitaka Oda, Shuya Mitoma, Jumpei Ito, Hesham Nasser, Jiri Zahradnik, Keiya Uriu, Shigeru Fujita, Yusuke Kosugi, Lei Wang, Masumi Tsuda, Mai Kishimoto, Hayato Ito, Rigel Suzuki, Ryo Shimizu, MST Monira Begum, Kumiko Yoshimatsu, Jiei Sasaki, Kaori Sasaki-Tabata, Yuki Yamamoto, Tetsuharu Nagamoto, Jun Kanamune, Kouji Kobiyama, Hiroyuki Asakura, Mami Nagashima, Kenji Sadamasu, Kazuhisa Yoshimura, Jin Kuramochi, Gideon Schreiber, Ken J Ishii, Takao Hashiguchi, The Genotype to Phenotype Japan (G2P-Japan) Consortium, Terumasa Ikeda, Akatsuki Saito, Takasuke Fukuhara, Shinya Tanaka, Keita Matsuno, Kei Satodoi: https://doi.org/10.1101/2022.05.26.493539
Abstract
After the global spread of SARS-CoV-2 Omicron BA.2 lineage, some BA.2-related variants that acquire mutations in the L452 residue of spike protein, such as BA.2.9.1 and BA.2.13 (L452M), BA.2.12.1 (L452Q), and BA.2.11, BA.4 and BA.5 (L452R), emerged in multiple countries.
Our statistical analysis showed that the effective reproduction numbers of these L452R/M/Q-bearing BA.2-related Omicron variants are greater than that of the original BA.2.
Neutralization experiments revealed that the immunity induced by BA.1 and BA.2 infections is less effective against BA.4/5. Cell culture experiments showed that BA.2.12.1 and BA.4/5 replicate more efficiently in human alveolar epithelial cells than BA.2, and particularly, BA.4/5 is more fusogenic than BA.2.
Furthermore, infection experiments using hamsters indicated that BA.4/5 is more pathogenic than BA.2. Altogether, our multiscale investigations suggest that the risk of L452R/M/Q-bearing BA.2-related Omicron variants, particularly BA.4 and BA.5, to global health is potentially greater than that of original BA.2.
Those interested can find the Sato Lab's twitter announcement, and analysis (in Japanese), in the following Threadreader capture.
How well this study's increased pathogenicity findings in hamsters will translate to humans remains to be seen, but this study suggests that with three legitimate rising threats, we may have a long, and active, COVID summer ahead.
