COVID-19 vaccine effectiveness in preventing severe outcomes and assessing the impact of prior SARS-CoV-2 infection among hospitalized adults in Albania, July 2022-July 2023.

The COVID-19 pandemic has significantly affected Albania, with over 319959 cases and 3625 deaths by December 2023. Despite a national vaccination campaign initiated in January 2021, only 44.1% of the eligible population had completed the full vaccination regimen by late 2023. In this study, we aim to estimate the effectiveness of COVID-19 vaccines in preventing severe outcomes and in assessing association of prior SARS-CoV-2 infection among adults hospitalized with COVID-19 in Albania. A test-negative case-control study was conducted using SARI sentinel surveillance data from July 2022 to July 2023. The study included 1858 hospitalized SARI patients aged 18 and older, with 410 testing positive for SARS-CoV-2 (cases) and 1448 testing negative (controls). Vaccine effectiveness was calculated using logistic regression, adjusting for age, sex, comorbidities, and hospital stay duration. The overall adjusted vaccine effectiveness (VE) for preventing hospitalization was 30.1% for those fully vaccinated with two doses and 31.4% for those with a booster. VE against severe outcomes was 30.6%, increasing to 37.8% after a booster. The highest VE was observed in patients aged 80 and above, reaching 52.5% after a booster. Prior SARS-CoV-2 infection combined with vaccination was associated with higher VE to 76.2%. However, many VE estimates had wide confidence intervals overlapping zero, indicating considerable uncertainty and lack of statistical significance in some subgroup results. This study provides real-world evidence of an association between COVID-19 vaccination, particularly with booster doses, and lower odds of severe outcomes. VE was highest among elderly patients and in those with prior SARS-CoV-2 infection, emphasizing the importance of booster campaigns in vulnerable populations.