evidence: Vaccination against COVID-19 started on 27 December 2020 across the European Union. By 31 August 2021, the EU reached the important milestone of 70% of the EU adult population getting fully vaccinated (one or two doses). EU countries continue their COVID-19 vaccination campaigns with booster shots and adapted vaccines to COVID-19 variants. [...] Vaccines work by preparing a person's immune system (the body’s natural defences) to recognise and defend itself against a specific disease. [...] When the immune system gets in contact with the inactivated virus it responds by producing natural defences against infection by COVID-19.