Issue with this (and other antibody tests) is both that levels of antibody vary wildly from person to person and across time.<p>The same person can show positive for a swab test, and then negative for antibody tests at months one and 2 and only start to show at month 3.<p>Equally some cases will never be revealed by an antibody test as the patient fought the virus solely with their T-cells - not antibodies.<p>-<p>This obviously doesn't mean that a cheap and reliable test is not of use - just that it will no doubt reveal more issues and edge cases with our understanding of the virus.