RATs most sensitive four days after symptom-onset

Rapid antigen tests are most sensitive to positive cases of COVID-19 four days after symptom-onset, US researchers have found.

According to their study involving 225 children and adults, the sensitivity of home testing kits peaked at 77% at the four-day mark compared with a same-day PCR test.

The overall sensitivity of rapid antigen tests (RATs) during the infectious period was a “moderate” 50%, said the Centers for Disease Control and Prevention researchers.

However, the predictive value significantly