The use and interpretation of rapid COVID-19 tests to reduce transmission is changing slightly with new variants and increased natural and vaccine-induced immunity in the population. A positive rapid test (even a very faint line) remains a good indicator of infectivity. However, some COVID-19 symptoms are now seen early in the disease course before the rapid test is positive. These are symptoms produced by the body’s immune response (something we now have due to natural or vaccine-induced immunity) to the virus – symptoms such as nasal congestion and runny nose, fever, sore throat. Symptoms produced by the virus damaging body cells (loss of taste or smell, diarrhea, shortness of breath) come later. Thus, if someone begins having scratchy throat and runny nose, rapid tests negative, and assumes they “just have a cold,” they may unwittingly build to a higher viral load in the next few days (that would turn a rapid test positive) and infect others with COVID-19. This is the reasoning behind recommendations for repeat testing 48 hours after an initial negative in symptomatic patients and for doing throat + nasal swabs to increase test sensitivity. For more info: and and follow Michael Mina @michaelmina_lab on Twitter.