The COVID-19 pandemic, caused by SARS-CoV-2, profoundly impacted global health systems and economies. Vaccination and diagnostic advancements were pivotal in managing the pandemic. This systematic review evaluates antibody levels in adults following complete COVID-19 vaccination and examines the prevalence of infections in vaccinated populations. A systematic review adhering to PRISMA guidelines was conducted, focusing on studies analyzing antibody levels at least 14 days after full vaccination with FDA- or EMA-approved vaccines. Five European studies meeting the inclusion criteria were selected. Data were extracted and synthesized from studies involving 6280 participants aged 19 to 105, with an average of 11% having prior exposure to SARS-CoV-2. Antibody levels were analyzed over time, and the incidence of post-vaccination COVID-19 cases was recorded. The reviewed studies demonstrated that antibody levels peaked shortly after vaccination but gradually declined over time. Individuals with prior SARS-CoV-2 infection exhibited higher antibody titers than those without prior exposure. After the first dose, the Pfizer-BioNTech vaccine led to significantly higher antibody levels than the Oxford-AstraZeneca vaccine, especially in those without prior infection. Across all studies, the incidence of COVID-19 among vaccinated individuals was low (0.1-3.8% for 144-302 days post-vaccination). Vaccination reduced severe outcomes despite decreasing antibody levels. The decline in new COVID-19 cases and related deaths is attributed to widespread vaccination, natural immunity, and virus mutations reducing severity. Further studies are warranted to explore antibody persistence and optimal vaccination strategies.