Question: It seems like a lot of COVID-19 transmission may be from asymptomatic carriers. How do we know that we’re not already all infected? Wouldn’t we just be locked down for nothing? Why can’t we reopen?

Answer: First, you’re right on the transmission front. There is increasing data showing that the virus is highly transmissible during the initial, asymptomatic/pre-symptomatic period. We also have recent findings from testing on the USS Roosevelt that ~350 of 600 sailors who test positive did not have symptoms. Given these findings, a person would do well to ask whether the coronavirus is far more contagious and far less deadly than originally thought — with most folks serving as unknowing viral hosts and only a small proportion of folks having serious symptoms and outcomes. We’ll that’s where it’s important to have time-trend data — like a prospective or retrospective study. Here we’d want to follow people who are asymptomatic when tested positive and examine whether symptoms come later (and how much later). Happily, we do have a few such datasets now. And what they are showing is that about 70%-80% who originally test positive while asymptomatic go on to develop symptoms (for more data/discussion, see Q&A of 4/3). So, based on what we know now, it’s very unlikely that most of us have already unknowingly had the virus. We would have had some symptoms. We also would have seen far higher numbers of deaths across the country, especially in non-epicenter areas. So while we still don’t know the true R0 or case fatality of COVID-19, nothing that we currently know would suggest that we’ve all already been exposed — that we’re already safe — and that we can simply reopen.

And this brings us back to why it’s so important to practice social distancing until we have widespread testing — if folks who feel fine are walking around spreading the virus, then simply telling sick people to stay home is NOT going to stop the pandemic. It also brings us back to why widespread testing is so important — if transmission occurs during a/pre-symptomatic period, then waiting to test someone until they have symptoms is too late! Because our country has not yet brought widespread testing to the fore and does not have the requisite contract tracers, if we reopened now, we’d basically be back in the same position we were in during February. It’s exceptionally infuriating that these necessary components of the response — testing, contact tracing — remain unfilled, especially recognizing the toll social distancing is taking.