The effectiveness of BNT162b2 mRNA vaccine against COVID-19 caused by Delta variant of SARS-CoV-2: a systematic review and meta-analysis.

Meta-analyses were utilized to determine the overall effectiveness of BNT162b2 mRNA vaccine (Pfizer vaccine) against COVID-19 caused by Delta variant from large real-world studies. A systematic literature search with no language restriction was performed in electronic databases to identify eligible observational studies that reported the effectiveness of the BNT162b2 mRNA vaccine to prevent reverse transcription-polymerase chain reaction (RT-PCR) confirmed COVID-19 caused by Delta variant of SARS-CoV-2 (B.1.617.2). Random-effects meta-analysis model was used to estimate the pooled odds ratio (OR) at a 95% confidence interval, and the vaccine effectiveness was indicated as (pooled OR - 1)/OR. Seven studies were included for this meta-analysis. The meta-analysis revealed that the administration of BNT162b2 mRNA vaccine protected against RT-PCR confirmed COVID-19 caused by Delta variant ≥ 21 days after the first dose, with vaccine effectiveness of 55% (95% confidence interval 46-63%), as well as ≥ 14 days after the second dose, with vaccine effectiveness of 81% (95% confidence interval 69-88%). In conclusion, the BNT162b2 mRNA vaccine offers a substantial protection rate against RT-PCR confirmed COVID-19 caused by the Delta variant upon full vaccination, albeit with slightly reduced effectiveness relative to other strains of SARS-CoV-2.