How accurate are the three types of tests for Covid-19?

This image provided by the US National Institute of Allergy and Infectious Diseases shows the SARS-CoV-2 virus (orange) emerging from the surface of normal cells (green) cultured in the lab. An antigen test detects the proteins of the virus in a person’s blood, but needs to be followed up with a PCR test for a confirmed diagnosis. — Photos: AP

Although much is known about tests for the SARS-CoV-2 virus that causes Covid-19, there is much more that is still unknown.

Prior to discussing the accuracy of these tests, it is important to know about the sensitivity and specificity of all tests, the infectivity of the SARS-CoV-2 virus and the body’s antibody response.