Exploring the effect of clinical case definitions on influenza vaccine effectiveness estimation at primary care level: Results from the end-of-season 2022–23 VEBIS multicentre study in Europe

• Published in: Vaccine Vol. 42; no. 16; pp. 3547 - 3554
• Main Authors: Maurel, Marine, Mazagatos, Clara, Goerlitz, Luise, Oroszi, Beatrix, Hooiveld, Mariette, Machado, Ausenda, Domegan, Lisa, Ilić, Maja, Popescu, Rodica, Sève, Noémie, Martínez-Baz, Iván, Larrauri, Amparo, Buda, Silke, Túri, Gergő, Meijer, Adam, Gomez, Verónica, O'Donnell, Joan, Mlinarić, Ivan, Timnea, Olivia, Diez, Ana Ordax, Dürrwald, Ralf, Horváth, Judit Krisztina, Dijkstra, Frederika, Rodrigues, Ana Paula, McKenna, Adele, Filipović, Sanja Kurečić, Lazar, Mihaela, Kaczmarek, Marlena, Bacci, Sabrina, Kissling, Esther
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 11-06-2024; Elsevier Limited; Elsevier Science
• Subjects: Adolescent; Adult; Age groups; Aged; Case-Control Studies; Child; Child, Preschool; Clinical case definition; COVID-19 vaccines; Effectiveness; Estimates; Europe - epidemiology; Female; Fever; Humans; Illnesses; Immunization; Infant; Infant, Newborn; Influenza; Influenza vaccine; Influenza Vaccines - administration & dosage; Influenza Vaccines - immunology; Influenza, Human - diagnosis; Influenza, Human - epidemiology; Influenza, Human - prevention & control; Male; Middle Aged; Multicenter study; Pandemics; Patients; Populations; Primary care; Primary Health Care - statistics & numerical data; Recruitment; Respiratory tract infection; Respiratory Tract Infections - diagnosis; Respiratory Tract Infections - epidemiology; Respiratory Tract Infections - prevention & control; Seasons; Surveillance; Test-negative design; Vaccination - statistics & numerical data; Vaccine effectiveness; Vaccine Efficacy; Vaccines; Young Adult; Europe; Sweden; Netherlands; Romania; Hungary; Ireland; France; Portugal; Germany; Croatia; Spain; EEA; VEBIS; I-MOVE; Multicenter study; ILI; GP; VE; EU; Test-negative design; Influenza; Vaccine effectiveness; Clinical case definition; ARI; Influenza vaccine; ECDC; WHO
• ISSN: 0264-410X; 1873-2518; 1873-2518
• DOI: 10.1016/j.vaccine.2024.04.060

Within influenza vaccine effectiveness (VE) studies at primary care level with a laboratory-confirmed outcome, clinical case definitions for recruitment of patients can vary. We used the 2022–23 VEBIS primary care European multicentre study end-of-season data to evaluate whether the clinical case definition affected IVE estimates.
We estimated VE using a multicentre test-negative case-control design. We measured VE against any influenza and influenza (sub)types, by age group (0–14, 15–64, ≥65 years) and by influenza vaccine target group, using logistic regression. We estimated IVE among patients meeting the European Union (EU) acute respiratory infection (ARI) case definition and among those meeting the EU influenza-like illness (ILI) case definition, including only sites providing information on specific symptoms and recruiting patients using an ARI case definition (as the EU ILI case definition is a subset of the EU ARI one).
We included 24 319 patients meeting the EU ARI case definition, of whom 21 804 patients (90 %) meet the EU ILI case definition, for the overall pooled VE analysis against any influenza. The overall and influenza (sub)type-specific VE varied by ≤2 % between EU ILI and EU ARI populations.
Among all analyses, we found similar VE estimates between the EU ILI and EU ARI populations, with few (10%) additional non-ILI ARI patients recruited. These results indicate that VE in the 2022–23 influenza season was not affected by use of a different clinical case definition for recruitment, although we recommend investigating whether this holds true for next seasons.