Tajima D test accurately forecasts Omicron / COVID-19 outbreak

AbstractOn 26 November 2021, the World Health Organization designated the SARS-CoV-2 variant B.1.1.529, Omicron, a variant of concern. However, the phylogenetic and evolutionary dynamics of this variant remain unclear. An analysis of the 131 Omicron variant sequences from November 9 to November 28, 2021 reveals that variants have diverged into at least 6 major subgroups. 86.3% of the cases have an insertion at amino acid 214 (INS214EPE) of the spike protein. Neutrality analysis of DH (−2.814, p<0.001) and Zeng’s E (0.0583, p=1.0) tests suggested that directional selection was the major driving force of Omicron variant evolution. The synonymous (Dsyn) and nonsynonymous (Dnonsyn) polymorphisms of the Omicron variant spike gene were estimated with Tajima’s D statistic to eliminate homogenous effects. Both D ratio (Dnonsyn/Dsyn, 1.57) and ΔD (Dsyn-Dnonsyn, 0.63) indicate that purifying selection operates at present. The low nucleotide diversity (0.00008) and Tajima D value (−2.709, p<0.001) also confirms that Omicron variants had already spread in human population for more than the 6 weeks than has been reported. These results, along with our previous analysis of Delta and Lambda variants, also supports the validity of the Tajima’s D test score, with a threshold value as −2.50, as an accurate predictor of new COVID-19 outbreaks.