Question: There’s one thing I don’t have a good handle on….. isn’t it possible that ANYONE could transmit the virus, regardless of their history (testing positive, negative, symptomatic, asymptotic, had it but recovered, etc.)? In other words, is everyone a potential transmitter at any given time?

Answer: One of the great challenges of COVID is that viral shedding begins before people exhibit symptoms, which means that people can be spreading the infection before they know they are sick with it (see Q&A of 6/9). A new systematic review on SARS-CoV-2 viral load and infectivity published in the Journal of Infection yesterday found “little to no difference in viral load between pre-symptomatic, asymptomatic and symptomatic patients.” Furthermore, the study authors conclude that “viral load of SARS-CoV-2 peaks around symptom onset or a few days thereafter, and becomes undetectable about two weeks after symptom onset…however the duration of infectivity remains uncertain.” The ability to unknowingly spread the virus makes common public health interventions — like telling people to stay home when sick or monitoring an individual’s temperature as they enter establishments — less effective at slowing the spread of the virus. Because of pre-/asymptomatic transmission risk, it is generally safest if each of us considers ourselves a potential risk to others and takes action to protect others — it makes wearing a face mask and keeping at least 6 feet apart all the more important and relevant. A couple of additional notes —

• Thus far, we have no evidence that people who have recovered from COVID can transmit the virus, even people who go on to test positive after having recovered (see Q&A from 5/19). We’re still learning as we go, so this is not definitive, but it is nonetheless positive. On this front, it’s important to do our utmost to avoid stigmatizing those who have been sick with COVID.
• When it comes to those who test positive for antibodies without having previously tested positive for COVID, we do not know whether: a) their antibody test result represents a true positive or false positive (see Q&A of 4/15); b) the antibodies they exhibit offer protection from the coronavirus; c) they can be (re)infected with coronavirus (see Q&A of 4/25). These folks should assume that they are at risk of becoming infected and infecting others.
• Status is not fixed. Just because a person tested negative several weeks ago does not mean that they remain negative. It is imperative that everyone, even those who have tested negative, practice behaviors that reduce risk, including and especially wearing a face mask, keeping 6+ feet apart, avoiding gatherings (especially indoors), washing hands, etc.