Effectiveness of COVID-19 vaccines against SARS-CoV-2 variants of concern: a systematic review and meta-analysis

Zeng, B.; Gao, L.; Zhou, Q.; Yu, K.; Sun, F.

Background. It was urgent and necessary to synthesize the evidence for vaccine effectiveness (VE) against SARS-CoV-2 variants of concern (VOC). We conducted a systematic review and meta-analysis to provide a comprehensive overview of the effectiveness profile of COVID-19 vaccines against VOC. Methods. Published and preprinted randomized controlled trials (RCTs), cohort studies, and case-control studies that evaluated the VE against VOC (Alpha, Beta, Gamma, or Delta) were searched until 31 August 2021. Pooled estimates and 95% confidence intervals (CIs) were calculated using random-effects meta-analysis. VE was defined as (1-estimate). Results. Seven RCTs (51,169 participants), 10 cohort studies (14,385,909 participants) and 16 case-control studies (734,607 cases) were included. Eight COVID-19 vaccines (mRNA-1273, BNT162b2, ChAdOx1, Ad26.COV2.S, NVX-CoV2373, BBV152, CoronaVac, and BBIBP-CorV) were included in this analysis. Full vaccination was effective against Alpha, Beta/Gamma, and Delta variants, with VE of 88.3% (95% CI, 82.4-92.2), 70.7% (95% CI, 59.9-78.5), and 71.6% (95% CI, 64.1-77.4), respectively. But partial vaccination was less effective, with VE of 59.0% (95% CI, 51.3-65.5), 49.3% (95% CI, 33.0-61.6), and 52.6% (95% CI, 43.3-60.4), respectively. mRNA vaccines seemed to have higher VE against VOC over others, significant interactions (pinteraction < 0.10) were observed between VE and vaccine type (mRNA vaccines vs. non-mRNA vaccines). Conclusions. Full vaccination of COVID-19 vaccines is highly effective against Alpha variant, and moderate effective against Beta/Gamma and Delta variants. Partial vaccination has less VE against VOC. mRNA vaccines seem to have higher VE against Alpha, Beta/Gamma, and Delta variants over others.