Does Home COVID-19 Testing Bias COVID-19 Vaccine Effectiveness Estimates?

Area of Science:

• Epidemiology
• Public Health
• Infectious Disease

Background:

• COVID-19 home testing became prevalent in early 2021.
• Home testing may impact care-seeking behaviors for acute respiratory illness.
• It can also influence the accuracy of COVID-19 vaccine effectiveness estimates.

Purpose of the Study:

• To assess the association between home COVID-19 testing and care-seeking behavior.
• To evaluate the impact of home testing on COVID-19 vaccine effectiveness estimates.
• To understand demographic and clinical factors associated with home testing.

Main Methods:

• A test-negative case-control study was conducted from January to May 2022.
• Outpatients with acute respiratory illness were surveyed about home COVID-19 testing and tested for SARS-CoV-2.
• Multivariable logistic regression analyzed associations between home testing, care seeking, and vaccine effectiveness.

Main Results:

• Home testing was associated with current vaccination, cough, higher education, and not having a prior positive test.
• COVID-19 illness correlated with cough, contact with a case, and home testing.
• Adjusted vaccine effectiveness was 35% (95% CI=22%, 45%), slightly increasing to 37% (95% CI=13%, 46%) when home testing was included. Effectiveness was lower in those who home tested (31%) versus those who did not (43%).

Conclusions:

• Patients utilizing home COVID-19 tests before seeking care differ from non-users.
• These differences can potentially bias estimates of COVID-19 vaccine effectiveness.
• Further research is needed to understand and account for these variations in specific populations.