  Rapid antigen tests detect proteins at the surface of virus particles,
identifying the disease during its infectious phase. In contrast, PCR tests
detect viral genomes; they can thus diagnose COVID-19 before the infectious
phase but also react to remnants of the virus genome, even weeks after live
virus ceases to be detectable in the respiratory tract. Furthermore, the
logistics for administering the tests are different, with rapid antigen tests
being much easier to administer at-scale. In this article, we discuss the
relative advantages of the different testing procedures and summarise evidence
that shows that using antigen tests 2-3 times per week could become a powerful
tool to suppress the COVID-19 pandemic. We also discuss the results of recent
large-scale rapid antigen testing in Austrian schools. While our report on
testing predates Delta, we have updated the review with recent data on viral
loads in breakthrough infections and more information about testing efficacy,
especially in children.
