Title Comparing two case definitions for including severe acute respiratory infection patients in influenza and COVID-19 vaccine effectiveness studies among older adults using the test-negative design: VEBIS hospital network, seven European countries, 2023/24
Authors Marques, Diogo F P ; Howard, Jennifer ; Álvarez, Marcos Lozano ; Machado, Ausenda ; Duffy, Róisín ; Túri, Gergő ; Kuliešė, Monika ; Popovici, Odette ; Petrović, Goranka ; Lajot, Adrien ; Dürrwald, Ralf ; Cauchi, John Paul ; Trobajo-Sanmartín, Camino ; Husa, Petr ; Pozo, Francisco ; Verdasca, Nuno ; Wagner, Eva Rivas ; Gómez, Verónica ; Fitzgerald, Margaret ; Oroszi, Beatrix ; Jančorienė, Ligita ; Lazar, Mihaela ; Tabain, Irena ; Genderini, Francesco G ; Hackmann, Carolin ; Džiugytė, Aušra ; Echeverria, Aitziber ; Součková, Lenka ; Nicolay, Nathalie ; Bacci, Sabrina ; Nunes, Baltazar ; Rose, Angela M C
DOI 10.1016/j.vaccine.2026.129234
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Is Part of Vaccine.. Oxford : Elsevier. 2026, vol. 94, art. no. 129234, p. [1-11].. ISSN 0264-410X. eISSN 1873-2518
Keywords [eng] Case definitions ; Multicentre study ; Severe acute respiratory infection (SARI) ; Test-negative design ; Vaccine effectiveness
Abstract [eng] INTRODUCTION: Two severe acute respiratory infection (SARI) case definitions (CDs) are often used in test-negative design (TND) hospital-based vaccine effectiveness (VE) studies. SARI-CD1 requires ≥1 symptom (cough, fever, shortness of breath, anosmia, ageusia, or dysgeusia); SARI-CD2 requires both fever and cough. Using VEBIS hospital network end-of-season 2023/24 data, we compared the effect of these CDs on influenza and COVID-19 VE estimates in Europe. METHODS: Using the TND, we restricted analysis to seven countries recruiting patients using SARI-CD1; we created a subset of SARI patients also meeting SARI-CD2. Cases were RT-PCR-positive for influenza A(H1N1)pdm09, A(H3N2), or SARS-CoV-2; controls were influenza or SARS-CoV-2 RT-PCR-negative. We estimated VE among patients ≥65 years using logistic regression adjusted for country, onset date, age, sex, and chronic conditions. We estimated VE overall, by age group (65-79, ≥80 years) and time since vaccination (14-59, 60-119, ≥120 days). Absolute VE differences ≥10% were considered relevant. RESULTS: Patient characteristics and outcomes were similar across CDs. SARI-CD1 had slightly more vaccinated cases, with little difference in controls between the two CDs. For influenza, the absolute VE difference between SARI-CD1 and SARI-CD2 was 10% for influenza A(H1N1)pdm09 (34% vs 44%), 19% among those aged ≥80 years (21% vs 40%) and 18% at 60-119 days post-vaccination (4% vs 22%). For SARS-CoV-2, absolute VE differences were 11% overall (29% vs 40%), 11% among ≥80 years (33% vs 44%), and 12% at 60-119 days (34% vs 46%). All other absolute VE differences were < 10%. CONCLUSIONS: VE was similar for influenza A(H3N2), adults 65-79 years and 14-60 days post-vaccination. We observed signals of higher VE with SARI-CD2 for influenza A(H1N1)pdm09 and SARS-CoV-2, particularly among adults ≥80 years and ≥ 60 days post-vaccination, although 95% CIs overlapped. These signals suggest CDs may contribute to VE variability and VE studies should clearly indicate CDs used.
Published Oxford : Elsevier
Type Journal article
Language English
Publication date 2026
CC license CC license description