A new form of Covid-19 test which can produce results in just 15-30 minutes is set to be rolled out across the globe. Here, we look at some of the key questions surrounding the rapid antigen tests. The new tests work by detecting proteins found on the surface of the virus. The tests, which look similar to pregnancy tests and can yield results within 30 minutes, simply display two blue lines for a positive result. The WHO last week approved the tests for emergency use.