Objectives: The highly transmissible COVID-19 delta variant (DV) has contributed to the surge in cases and has now been exacerbated the worldwide public health crisis. Several COVID-19 vaccines play a significant role in a high degree of protection against DV. The primary purpose of this meta-analysis is to estimate the pooled effectiveness of the COVID-19 vaccines against 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 of COVID-19 vaccines against B.1.617.2 clinical perspective among fully COVID-19 vaccinated populations, compared to placebo (unvaccinated populations), published before September 30, 2021. Eleven studies containing 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 delta variant 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 peoples) were screened for the COVID-19 vaccines' effectiveness against delta variant. We found 61.13% of study population were fully vaccinated with 2-dose of COVID-19 vaccines. Weighted pooled incidence of COVID-19 infection was more than double (20.07%) among unvaccinated populations, compared to the fully vaccinated population (8.16%). Overall, the effectiveness of COVID-19 vaccine against 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. Conclusion: Effectiveness COVID-19 vaccines were noted to offer higher protection against delta variant among populations who received two vaccine doses compared with unvaccinated populations. 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 to have herd immunity to breat the chain of transmission and gain greater overall population protection more rapidly.
Effectiveness of COVID-19 vaccines against delta variant (B.1.617.2): A meta-analysis