Review Article

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).

Conclusions: 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.

1. Liu H, Zhang J, Cai J, Deng X, Peng C, Chen X, et al. Herd immunity induced by COVID-19 vaccination programs to suppress epidemics caused by SARS-CoV-2 wild type and variants in China. 2021.
2. Sheikh A, McMenamin J, Taylor B,Robertson CJTL. SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital
admission, and vaccine effectiveness. 2021.
3. Zhang M, Xiao J, Deng A, Zhang Y, Zhuang Y, Hu T, et al. Transmission Dynamics of an Outbreak of the COVID-19 Delta Variant B. 1.617. 2—Guangdong Province, China,May–June 2021. 2021;3(27):584-6.
4. Heesterbeek J, Dietz KJSn. The concept of Ro in epidemic theory. 1996;50(1):89-110.
5. Viceconte G, Petrosillo N. COVID-19 R0: Magic number or conundrum? : Multidisciplinary Digital Publishing Institute;
6. Ahammed T, Anjum A, Rahman MM, Haider N, Kock R, Uddin MJ. Estimation of novel coronavirus (COVID‐19) reproduction number and case fatality rate: A systematic review and meta‐analysis. Health science reports. 2021;4(2):e274.
7. Jackson D, Bowden J, Baker R. How does the DerSimonian and Laird procedure for random effects meta-analysis compare with its more efficient but harder to compute counterparts? Journal of Statistical Planning and Inference. 2010;140(4):961-70.
8. Higgins JP, Thompson SG. Quantifying heterogeneity in a meta‐analysis. Statistics in medicine. 2002;21(11):1539-58.
9. Higgins JP, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, et al. Cochrane handbook for systematic reviews of
interventions: John Wiley & Sons; 2019.
10. DerSimonian R, Laird N. Meta-analysis in clinical trials. Controlled clinical trials. 1986;7(3):177-88.
11. Chang SL, Cliff OM, Prokopenko MJapa. Nowcasting transmission and suppression of the Delta variant of SARSCoV-
2 in Australia. 2021.
12. Kang M, Xin H, Yuan J, Ali ST, Liang Z, Zhang J, et al. Transmission dynamics and epidemiological characteristics of Delta variant infections in China. 2021.
13. Qingfeng Shi XG, Bijie Hu. Research progress on characteristics, epidemiology and control measure of SARS-CoV-2 Delta VOC. Chin J Nosocomiol. 2021;31.
14. Head JR, Andrejko KL, Remais JVJm. Model-based assessment of SARS-CoV-2 Delta variant transmission dynamics within partially vaccinated K-12 school populations. 2021.
15. Pandemic Influenza Group on Modelling Os-g. SPI-M-O: Summary of further modelling of easing restrictions – Roadmap Step 4 [updated 9 june 2021]. 21:[Available from: publications/spi-m-o-summary-of-furthermodelling- of-easing-restrictions-roadmapstep- 4-9-june-2021.
16. Bae HW, Lee SY, Kim SJ, Shin HK,Choi BT, Baek JU. Selecting effective herbal medicines for attention-deficit/hyperactivity disorder via text mining of donguibogam. Evidence-Based Complementary and Alternative Medicine. 2019;2019.
17. Alimohamadi Y, Taghdir M, Sepandi MJJoPM, Health P. Estimate of the basic reproduction number for COVID-19: a
systematic review and meta-analysis. 2020;53(3):151.
18. Liu Y, Gayle AA, Wilder-Smith A, Rocklöv JJJotm. The reproductive number of COVID-19 is higher compared to SARS
coronavirus. 2020.
19. Liu Y, Rocklöv JJJoTM. The reproductive number of the Delta variant of SARS-CoV-2 is far higher compared to the
ancestral SARS-CoV-2 virus. 2021.
20. Fisman D, Tuite AJm. Progressive Increase in Virulence of Novel SARS-CoV-2 Variants in Ontario, Canada, February to June, 2021. 2021.
21. Abu-Raddad LJ, Chemaitelly H, Yassine HM, Benslimane FM, Al Khatib HA, Tang P, et al. Pfizer-BioNTech mRNA BNT162b2 Covid-19 vaccine protection against variants of concern after one versus two doses. 2021;28.
22. Bernal JL, Andrews N, Gower C, Gallagher E, Simmons R, Thelwall S, et al. Effectiveness of Covid-19 vaccines against the B. 1.617. 2 (Delta) variant. 2021.
23. Shim E. Projecting the impact of SARS-CoV-2 variants and the vaccination program on the fourth wave of the COVID-19 pandemic in South Korea. International Journal of Environmental Research and PublicHealth.2021;18(14):7578.
24. Ryu S, Kim D, Lim J-S, Ali ST, Cowling BJ. Serial interval and transmission dynamics during the SARS-CoV-2 Delta variant predominance in South Korea. medRxiv. 2021:2021.08. 18.21262166.
25. Delamater PL, Street EJ, Leslie TF, Yang YT, Jacobsen KHJEid. Complexity of the basic reproduction number (R0). 2019;25(1):1.
26. Ridenhour B, Kowalik JM, Shay DKJAjoph. Unraveling r 0: Considerations for public health applications.
IssueVol 8 No 1 (2022) QRcode
SectionReview Article(s)
Basic Reproduction Number Delta variant SARS-CoV-2 Covid‐19

Rights and permissions
Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
How to Cite
Sepandi M, Alimohamadi Y, Esmaeilzadeh F. Estimate of the Basic Reproduction Number for Delta variant of SARS-CoV-2: A Systematic Review and Meta-analysis. JBE. 2022;8(1):1-7.