Does home COVID-19 testing bias COVID-19 vaccine effectiveness estimates?

Publication date: Sep 11, 2025

COVID-19 home testing became widely available in early 2021. Care seeking for acute respiratory illness (ARI), and COVID-19 vaccine effectiveness (VE) estimates may be affected by home testing. In a test-negative case-control study, between January-May 2022, U. S. Flu VE Network outpatients were asked about their home COVID-19 testing before seeking care for ARI and were laboratory tested for SARS-CoV-2. Associations among home testing, care seeking and COVID-19 VE were assessed using multivariable logistic regression. Among 2,614 enrollees, home COVID-19 testing was significantly associated with current (≤6 months) COVID-19 vaccination (adjusted odds ratio (aOR=1. 70; 95%CI=1. 19-2. 42); cough (aOR=1. 69; 1. 22-2. 34) and having a college degree or higher (aOR=1. 67; 1. 37-2. 03) and negatively associated with a prior positive COVID-19 test. COVID-19 illness was associated with cough (aOR=3. 07; 2. 04-4. 61), contact with a COVID-19 case (aOR=2. 41; 1. 93-3. 0), home testing (aOR=1. 87; 1. 53-2. 29) and negatively associated with a prior positive COVID-19 test. In unadjusted modeling with only the association between current vaccination and COVID-19 infection, the OR was 0. 77 (95% CI=0. 66, 0. 92); adjusting for patient race/ethnicity, age, days from onset to enrollment, prior COVID-19 illness and study site, the aOR was 0. 65 (0. 55, 0. 78); estimated VE=35% (95%CI=22%-45%). Adding home testing to this adjusted model, VE was 37% (95%CI=13%-46%). Among patients who home tested, VE was 31% (13%-46%) versus 43% (24%-57%) among patients who did not. Patients reporting home testing for COVID-19 before seeking outpatient care for ARI differed from patients not using home tests, which could affect estimates of COVID-19 VE in some populations.

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