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.