Effectiveness of COVID-19 Vaccines against Delta (B.1.617.2) Variant: A Systematic Review and Meta-Analysis of Clinical Studies
Ali Pormohammad,
Mohammad Zarei,
Saied Ghorbani,
Mehdi Mohammadi,
Saeideh Aghayari Sheikh Neshin,
Alireza Khatami,
Diana L. Turner,
Shirin Djalalinia,
Seied Asadollah Mousavi,
Heydar Ali Mardani-Fard,
Amir Kasaeian,
Raymond J. Turner
Affiliations
Ali Pormohammad
Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
Mohammad Zarei
Renal Division, Brigham & Women’s Hospital, Harvard Medical School, Boston, MA 02115, USA
Saied Ghorbani
Department of Virology, Faculty of Medicine, Iran University of Medical Science, Tehran 1449614535, Iran
Mehdi Mohammadi
Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
Saeideh Aghayari Sheikh Neshin
Neuroscience Research Center, Guilan University of Medical Sciences, Rasht 4188794755, Iran
Alireza Khatami
Department of Virology, Faculty of Medicine, Iran University of Medical Science, Tehran 1449614535, Iran
Diana L. Turner
Department of Family Medicine, Cumming School of Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada
Shirin Djalalinia
Deputy of Research and Technology, Ministry of Health and Medical Education, Tehran 1467664961, Iran
Seied Asadollah Mousavi
Hematology, Oncology and Stem Cell Transplantation Research Center, Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran 1411713131, Iran
Heydar Ali Mardani-Fard
Department of Mathematics, Yasouj University, Yasouj 7493475918, Iran
Amir Kasaeian
Hematology, Oncology and Stem Cell Transplantation Research Center, Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran 1411713131, Iran
Raymond J. Turner
Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
The high transmissibility, mortality, and morbidity rate of the SARS-CoV-2 Delta (B.1.617.2) variant have raised concerns regarding vaccine effectiveness (VE). To address this issue, all publications relevant to the effectiveness of vaccines against the Delta variant were searched in the Web of Science, Scopus, EMBASE, and Medline (via PubMed) databases up to 15 October 2021. A total of 15 studies (36 datasets) were included in the meta-analysis. After the first dose, the VE against the Delta variant for each vaccine was 0.567 (95% CI 0.520–0.613) for Pfizer-BioNTech, 0.72 (95% CI 0.589–0.822) for Moderna, 0.44 (95% CI 0.301–0.588) for AstraZeneca, and 0.138 (95% CI 0.076–0.237) for CoronaVac. Meta-analysis of 2,375,957 vaccinated cases showed that the Pfizer-BioNTech vaccine had the highest VE against the infection after the second dose, at 0.837 (95% CI 0.672–0.928), and third dose, at 0.972 (95% CI 0.96–0.978), as well as the highest VE for the prevention of severe infection or death, at 0.985 (95% CI 0.95–0.99), amongst all COVID-19 vaccines. The short-term effectiveness of vaccines, especially mRNA-based vaccines, for the prevention of the Delta variant infection, hospitalization, severe infection, and death is supported by this study. Limitations include a lack of long-term efficacy data, and under-reporting of COVID-19 infection cases in observational studies, which has the potential to falsely skew VE rates. Overall, this study supports the decisions by public health decision makers to promote the population vaccination rate to control the Delta variant infection and the emergence of further variants.
