Primary COVID-19 vaccine cycle and booster doses efficacy: analysis of Italian nationwide vaccination campaign.

We provide here an updated analysis of primary COVID-19 vaccination and vaccine booster doses efficacy, emerging from the ongoing Italian nationwide COVID-19 vaccination campaign. Primary COVID-19 vaccination efficacy was 76-92% within 6 months, decreasing to 34-80% after 6 months. Administration of vaccine booster doses decreased SARS-CoV-2 infections by 65%, COVID-19-related hospitalizations and deaths by 69% and 97% compared with vaccine efficacy after 6 months, but also decreased SARS-CoV-2 infections by 39% compared with vaccine efficacy within 6 months. These results suggest that COVID-19 vaccine booster doses are important for restoring vaccine efficacy and further limiting virus circulation.