Evaluating the role of self-collected home swab data in enhancing influenza vaccine effectiveness estimates in general practice

This study evaluated the feasibility of utilising general practitioner (GP)-initiated, laboratory-confirmed self-collected home swab data (iSwab) for estimating influenza vaccine effectiveness (VE), compared to traditional health practitioner-collected swabs for surveillance. Demographic, clinical, and vaccination profiles of iSwab patients were compared to patients whose swabs were collected by a practitioner in an established GP surveillance network (Australian Sentinel Practices REsearch Network, ASPREN). VE estimates for both groups were calculated using a test-negative design and logistic regression. ASPREN patients had a lower median age (37 years) compared to iSwab (42 years) and a lower vaccination rate (37 % vs. 47 %). iSwab patients were more likely to have missing data than the ASPREN cohort. Pathogen detection rates varied between the two sampling methods. ASPREN had higher influenza positivity compared to iSwab, especially in 2022. VE estimates varied between the two methods, with ASPREN demonstrating moderate effectiveness in both years. iSwab VE was unable to be calculated in 2022 due to small sample size, while in 2023 it was higher than the ASPREN estimates. Combining data from both methods provided more precise VE estimates. However, population differences in the iSwab cohort question the validity of the combined estimates. Self-collected home swabs, initiated by GPs, have the potential to complement traditional systems for VE estimation. Differences in demographics, vaccination rates, and data completeness between the two methods highlight the need for systematic sampling to prevent selection bias in the self-swabbing cohort to ensure accuracy of VE estimates before combining data from these two methods.