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Review
. 2022 Feb 11;10(2):277.
doi: 10.3390/vaccines10020277.

Effectiveness of COVID-19 Vaccines against Delta Variant (B.1.617.2): A Meta-Analysis

Rashidul Alam Mahumud  1   2   3 , Mohammad Afshar Ali  2   4   5 , Satyajit Kundu  6   7 , Md Ashfikur Rahman  8 , Joseph Kihika Kamara  9   10 , Andre M N Renzaho  11   12
Affiliations
Review

Effectiveness of COVID-19 Vaccines against Delta Variant (B.1.617.2): A Meta-Analysis

Rashidul Alam Mahumud et al. Vaccines (Basel). .

Abstract

Objectives: The highly transmissible COVID-19 Delta variant (DV) has contributed to a surge in cases and exacerbated the worldwide public health crisis. Several COVID-19 vaccines play a significant role in a high degree of protection against the DV. The primary purpose of this meta-analysis is to estimate the pooled effectiveness of the COVID-19 vaccines against the DV in terms of risk ratio (RR) among fully vaccinated, compared to unvaccinated populations. Methods: We carried out a systematic review, with meta-analysis of original studies focused on COVID-19 vaccines effectiveness against a DV clinical perspective among fully COVID-19 vaccinated populations, compared to placebo (unvaccinated populations), published between 1 May 2021 and 30 September 2021. Eleven studies containing the data of 17.2 million participants were identified and included in our study. Pooled estimates of COVID-19 vaccines effectiveness (i.e., risk ratio, RR) against the DV with 95% confidence intervals were assessed using random-effect models. Publication bias was assessed using Egger's regression test and funnel plot to investigate potential sources of heterogeneity and identify any differences in study design. Results: A total population of 17.2 million (17,200,341 people) were screened for the COVID-19 vaccines' effectiveness against the DV. We found that 61.13% of the study population were fully vaccinated with two doses of COVID-19 vaccines. The weighted pooled incidence of COVID-19 infection was more than double (20.07%) among the unvaccinated population, compared to the fully vaccinated population (8.16%). Overall, the effectiveness of the COVID-19 vaccine against the DV was 85% (RR = 0.15, 95% CI: 0.07-0.31). The effectiveness of COVID-19 vaccines varied slidably by study designs, 87% (RR = 0.13, 95% CI: 0.06-0.30) and 84% (RR = 0.16, 95% CI: 0.02, 1.64) for cohort and case-control studies, respectively. Conclusions: The effectiveness of COVID-19 vaccines were noted to offer higher protection against the DV among populations who received two vaccine doses compared with the unvaccinated population. This finding would help efforts to maximise vaccine coverage (i.e., at least 60% to 70% of the population), with two doses among vulnerable populations, in order to have herd immunity to break the chain of transmission and gain greater overall population protection more rapidly.

Keywords: B.1.617.2; COVID-19 vaccines; delta variant; herd immunity; meta-analysis; vaccines effectiveness.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Steps of study selection procedures.
Figure 2
Figure 2
Effectiveness of the two-dose COVID-19 vaccines against the Delta variant.
Figure 3
Figure 3
Assessing publication bias.
See this image and copyright information in PMC

References

    1. Sheikh A., McMenamin J., Taylor B., Robertson C. SARS-CoV-2 Delta VOC in Scotland: Demographics, risk of hospital admission, and vaccine effectiveness. Lancet. 2021;397:2461–2462. doi: 10.1016/S0140-6736(21)01358-1. - DOI - PMC - PubMed
    1. GISAID Delta Variant Detected Across 185 Countries. Global Initiative on Sharing Avian Influenza Data (GIAID). Phylodynamics Pandemic Coronavirus Var. VOC Delta G/478K.V1 First Detect. India. 2021. [(accessed on 30 September 2021)]. Available online: https://www.gisaid.org/hcov19-variants/
    1. Gallagher J. COVID: Is There a Limit to How Much Worse Variants Can Get? How the R0 Numbers of COVID-19 Variants and Other Diseases Compare. 2021. [(accessed on 30 September 2021)]. Available online: https://www.bbc.com/news/health-57431420.
    1. Krause P.R., Fleming T.R., Peto R., Longini I.M., Figueroa J.P., Sterne J.A.C., Cravioto A., Rees H., Higgins J.P.T., Boutron I., et al. Considerations in boosting COVID-19 vaccine immune responses. Lancet. 2021;6736:21–24. doi: 10.1016/S0140-6736(21)02046-8. - DOI - PMC - PubMed
    1. Callaway E. COVID vaccine boosters: The most important questions. Nature. 2021;596:178–180. doi: 10.1038/d41586-021-02158-6. - DOI - PubMed

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