RESUMO
BACKGROUND AND IMPORTANCE: Rapid antigen point-of-care tests (antigen POC tests) are frequently used to detect COVID-19 infections. Based on clinical impressions, we suspected that the sensitivity of antigen POC tests might be lower in vaccinated patients. OBJECTIVE: To evaluate the sensitivity of antigen POC tests in vaccinated patients. DESIGN, SETTING AND PARTICIPANTS: We retrospectively evaluated all patients over 18 years of age that tested positive for severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) in November 2021 at our institution, whose antigen POC test result had been recorded. We considered patients who were either fully vaccinated or unvaccinated, as well as whether they were symptomatic. OUTCOME MEASURE AND ANALYSIS: We calculated the sensitivity of antigen POC tests in vaccinated and unvaccinated as well as in symptomatic and asymptomatic patients and compared the results. RESULTS: A total of 4080 reverse transcription PCR tests were performed in our institution in November 2021, of which 360 patients tested positive for SARS-CoV-2. Of those, 234 patients met inclusion criteria and were further evaluated. The sensitivity of the antigen POC test was only 39.4% [95% confidence interval (CI), 31.3-48.1%] in vaccinated patients and differed significantly from the sensitivity of 53.3% (95% CI, 43.9-62.4%) in unvaccinated patients (difference of sensitivities, 13.9%; 95% CI, 1.1-26.1%). In symptomatic patients, the sensitivity increased by only 11.8% from 45.7% in all patients (95% CI, 39.5-52.1%) to 57.5% in symptomatic patients (95% CI, 49.9-64.7%). In asymptomatic patients, the antigen POC test was only able to detect SARS-CoV-2 positive patients in 16.4% of the cases (95% CI, 9.4-27.1%). CONCLUSION: Point-of-care antigen tests are likely not useful for ruling out SARS-CoV-2 infection, especially in vaccinated and asymptomatic patients, potentially due to lower viral load. Moreover, the use of these tests might lead to a false sense of security, especially when used by the public as part of a public health testing strategy.
