Effectiveness of mRNA and viral-vector vaccines in epidemic period led by different SARS-CoV-2 variants: A systematic review and meta-analysis.

We assessed the effectiveness of mRNA and viral-vector vaccines in epidemic period led by different SARS-CoV-2 variants. Systematic search of PubMed, EMBASE, and CNKI (China National Knowledge Infrastructure) databases without language restriction for studies published before September 19, 2022. The review was registered with PROSPERO (CRD42022335430) and reported according to PRISMA guidelines. Forty studies met the inclusion criteria for this study, with 62 954 861 participants. The overall vaccine effectiveness (VE) to prevent COVID-19 infection was 0.76 (95% confidence interval [CI] 0.73-0.78), symptomatic infection was 0.87 (95% CI 0.83-0.91), hospital admissions was 0.82 (95% CI 0.75-0.87), and mortality was 0.76 (95% CI 0.48-0.89). Subgroup analysis were performed to characterize the effectiveness of different vaccines. When SARS-CoV-2 variants are taking account, the VE decreased along with the variation of the virus by clinical outcomes and vaccine types. The findings of this systematic review provide the best available evidence that BNT162b2, mRNA-1273, ChAdOx1, and Ad26. COV2.S seems to be approximately effective from predelta to omicron, but only modestly effective in participants aged 65 or older. When SARS-CoV-2 variants are taking account, VE decreased along with the variation of the virus for all mRNA and viral-vector vaccines.