Estimate of the Basic Reproduction Number for Delta variant of SARS-CoV-2: A Systematic Review and Meta-analysis

Introduction: An essential concept in assessing the extent to which an infectious outbreak spread is the concept of basic reproductive number (R0 ). The current systematic review and meta-analysis aimed to estimate the R0 of the Delta variant of SARS-CoV-2 based on studies published from 1 January 2021 to 23 September 2021. Methods: International databases (including Google Scholar, Science Direct, PubMed, and Scopus) were searched using keywords: "Basic reproduction number, R0 , COVID-19, SARS-COV-2, Severe Acute Respiratory Syndrome Coronavirus, NCOV, 2019 NCOV, coronavirus, Delta variant, B.1.617.2". Due to significant heterogeneity, DerSimonian-Laird random-effects model was used to estimate the pooled value of R0 . Results: A total of 245 reports were identified. After assessing the inclusion criteria, three studies were selected. The pooled R0 for the Delta variant was estimated as 5.10 (95% CI, 3.04 to 7.17), (I2 =86.77%, T2 :2.68, p-value from the chi-square test for heterogeneity was<0.001). Conclusion: Considering the estimated value of R0 for the Delta variant of SARS-CoV-2, the amount of vaccine coverage required to achieve herd immunity appears to be higher than previous variants of the virus.