COVID-19 Vaccine Effectiveness Against Hospitalizations and Severe Outcomes in Kosovo, 2022–2024: A Test-Negative Case–Control Study

Background

Few studies have evaluated COVID-19 vaccine effectiveness (VE) in middle-income countries, particularly in eastern Europe. We aimed to estimate COVID-19 VE against SARS-CoV-2-confirmed hospitalizations and severe outcomes in Kosovo.

Methods

We conducted a test-negative case–control study using data from Kosovo's severe acute respiratory infection (SARI) sentinel surveillance system from January 2022 to June 2024. We enrolled adult patients aged ≥ 18 years hospitalized with SARI. From all patients, we collected clinical data, vaccination history, and a nasopharyngeal specimen, which was tested for SARS-CoV-2 using RT-PCR. SARS-CoV-2-positive patients were cases; those testing negative were controls. We estimated VE overall and against severe outcomes (requiring oxygen, intensive care admission, or in-hospital death) using logistic regression, adjusting for age, sex, and comorbidities, calculating VE as (1–adjusted odds ratio) × 100.

Results

We included 564 SARI patients; 218 (39%) tested positive for SARS-CoV-2. Overall, 24% of SARI patients had received at least one COVID-19 vaccine dose in the previous 12 months. VE against SARS-CoV-2-confirmed SARI hospitalization among all adults was 72% (95% CI: 30%–89%) at 14–179-day postvaccination, and 26% (95% CI: −33%–59%) at 180–364 days. In adults ≥ 60 years, VE was 52% (95% CI:−31%–82%) at 14–179-day postvaccination, and −36% (95% CI: −190%–36%) at 180–364 days. VE against severe outcomes was 67% (95% CI: −14%–91%) at 14–179 days, and 17% (95% CI:−111%–67%) at 180–364 days.

Conclusions

Our findings suggest that COVID-19 vaccination in Kosovo offered substantial protection against hospitalization and severe outcomes within 6 months, though confidence intervals were wide for some subgroups. Effectiveness waned after 6 months, highlighting the need for periodic booster doses.