This report addresses the most relevant data on COVID-19 vaccines literature as of 27 September 2021. The current report addresses vaccine effectiveness against the Delta (B.1.617.2) variant, methodological issues in assessing vaccine effectiveness, an in-depth overview of both mRNA vaccines (Pfizer-BioNTech and Moderna), protection of booster doses against COVID-19 infections, the effects of vaccination on transmissibility of SARS-CoV-2, the characteristics of breakthrough infections, and maternal vaccinations. To conclude, the report highlights the latest SARS-CoV-2 vaccine development information on COVID-19 vaccine candidates.