Full vaccination against COVID-19 suppresses SARS-CoV-2 delta variant and spike gene mutation frequencies and generates purifying selection pressure

COVID-19 vaccination resistance has become a major challenge to prevent global SARS-CoV-2 transmission. Here we report that the vaccination coverage rate is inversely correlated to the mutation frequency of the full genome (R2=0.878) and spike gene (R2=0.829) of SARS-CoV-2 delta variants in 16 countries, suggesting that full vaccination against COVID-19, with other mitigation strategies, is critical to suppress emergent mutations. Neutrality analysis of DH and Zeng E tests suggested that directional selection was the major driving force of delta variant evolution. To eliminate the homogenous effects (population expansion, selective sweep etc.), the synonymous (Dsyn) and nonsynonymous (Dnonsyn) polymorphisms of the delta variant spike gene were estimated with Tajima D statistic. Both D ratio (Dnonsyn/Dsyn) and deltaD (Dsyn-Dnonsyn) have positive correlation with the full vaccination rate (R2= 0.723 and 0.505, respectively) in 19 countries, indicating that purifying selection pressure of SARS-CoV-2 spike gene increased as the vaccination coverage rate increased. Taken together, our data suggests that vaccination plays an important role in the purifying selection force of spike protein of SARS-CoV-2 delta variants.