We estimated COVID-19 vaccine effectiveness (VE) against PCR-confirmed SARS-CoV-2 hospitalisation in patients ≥60 years with severe acute respiratory infection, using a multicentre, test-negative case-control study across six European countries between September 2024 and May 2025. We included 352 cases (115 vaccinated; 33%) and 9 980 controls (5 024 vaccinated; 50%). VE was 42% (95%CI:15;61) 14–59 days post-vaccination, 32% (95%CI: -1;54) at 60–119 days, and 36% (95%CI: 2;60) at 120–179 days, and no effect thereafter. Among adults aged 60–79 and ≥80 years, we observed moderate VE against COVID-19 hospitalisation for up to 2 and 4 months, respectively.

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 75% (95%CI:37–90%) at 14–179 days post-vaccination, and 24% (95% CI:-35–58%) at 180–364 days. In adults ≥60 years, VE was 59% (95%CI:-10–84%) at 14–179 days post-vaccination, and -37% (95%CI:-188–5%) at 180–364 days. VE against severe outcomes was 70% (95% CI:-2–91%) at 14–179 days, and 8% (95%CI:-128–63%) at 180–364 days. Conclusions: In Kosovo, COVID-19 vaccination offered significant protection against hospitalization and severe outcomes. Effectiveness waned after 6 months, highlighting the need for periodic booster doses.

We estimated the effectiveness of the adapted monovalent XBB.1.5 COVID-19 vaccines against PCR-confirmed SARS-CoV-2 hospitalisation during the BA.2.86/JN.1 lineage-predominant period using a multicentre test-negative case-control study in Europe. We included older adults (≥65 years) hospitalised with severe acute respiratory infection from November 2023 to May 2024. Vaccine effectiveness was 46% at 14–59 days, 34% at 60–119 days, with no effect thereafter. The XBB.1.5 COVID-19 vaccines conferred protection against BA.2.86 lineage hospitalisation in the first 4 months post vaccination.

We conducted a multicentre test-negative case-control study covering the period from October 2023 to January 2024 among adult patients aged ≥18 years hospitalised with severe acute respiratory infection in Europe. We provide early estimates of the effectiveness of the newly adapted XBB.1.5 COVID-19 vaccines against PCR-confirmed SARS-CoV-2 hospitalisation. Vaccine effectiveness was 48% overall, ranging between 68% at 14–29 days and 40% at 60–105 days post vaccination. The adapted XBB.1.5 COVID-19 vaccines conferred protection against COVID-19 hospitalisation in the first 3.5 months post vaccination, with VE >70% in older adults (≥65 years) up to 1 month post vaccination.

We conducted a multicentre hospital-based test-negative case–control study to measure vaccine effectiveness (VE) against PCR-confirmed influenza in adult patients with severe acute respiratory infection (SARI) during the 2022/23 influenza season in Europe. Among 5547 SARI patients ≥18 years, 2963 (53%) were vaccinated against influenza. Overall VE against influenza A(H1N1)pdm09 was 11% (95%CI: -23–36); 20% (95%CI: -4–39) against A(H3N2) and 56% (95%CI: 22–75) against B. During the 2022/23 season, while VE against hospitalisation with influenza B was >55%, it was ≤20% for influenza A subtypes. While influenza vaccination should be a priority for the upcoming season, improved vaccines against influenza are needed.