Another Stunner: Asymptomatic People Can’t Transmit COVID?
I’ve been blogging on COVID lately because we’re just starting to see large, high-quality studies published. The one I’ll cover this morning is yet another stunner that upends everything we think we know about how COVID-19 is transmitted. It also has massive public health implications. Let’s dig in.
What We Know About How COVID-19 Is Transmitted
What know about COVID-19 transmission comes from small studies or contact tracing. As I have said in the past, contact tracing has serious room for error. Meaning, even in our limited almost locked down COVID world of today, if you leave your house to do some limited holiday shopping this weekend or go to an outdoor restaurant or even Target, you’ll still come in contact with a massive number of people. If you get COVID and have a contact tracer assigned to you, how will you know which of those people gave you COVID-19? From a scientific standpoint, it’s a mess multiplied by a big mess which equals a massive mess. Meaning, we don’t know much with certainty about how this disease is transmitted.Request a Regenexx Appointment
Is Asymptomatic Transmission a Thing?
Asymptomatic means no symptoms. The information on whether you can be asymptomatic and transmit this disease is all over the place. That’s why a very large study out of Wuhan, China may help be the tiebreaker (1). This new study was just published in Nature, which is a top tier journal. The title here tells you that this study represents an immense amount of work:
“Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China”
Yes, you read that right, this was a study based on the lab test results of ten million people. So the mantra of this new research is “Go big or go home”.
This research consisted of a city-wide SARS-CoV-2 screening program between May 14 and June 1, 2020 in Wuhan, China. They tested 9,899,828 people, which was a 93% participation rate! There’s nothing quite like a totalitarian society when you’re collecting clinical research data!
They detected no new symptomatic cases at this point after their lockdown. They did find 300 asymptomatic cases. Of note, there were no positive tests among the 1,174 close contacts of asymptomatic cases. This is really important, that they found no transmission from an asymptomatic person to a close contact.
Why should we trust this contact tracing? This type only tried to determine if the “close contacts” (usually people living together) could transmit the disease to each other, which would be much more accurate than “all contacts”. Hence, this data is more likely to be sound.
Was this Testing Good?
While the Chinese authors used the same crazy number of amplification cycles (about 37) for their PCR test, they did take the time to grow out the virus from asymptomatic positives. Meaning they did a better job than most in trying to make sure these patients actually had a living virus in their nose that was capable of replicating itself.
What Does this Study Tell Us?
This study, which is the largest of its kind to date, tells us that locking down asymptomatic people because they have a positive COVID-19 test is futile. Until a better study comes along, this is the one we should be using to drive US public policy. So unless you have symptoms, there is no current scientific rationale for a quarantine.
A Summary of What We Know Based on this Trio of Studies
I’ve covered three large COVID-19 studies in the past week and here’s what they tell us (these studies based on their size and quality supersede all of the other studies we have):
- COVID-19 spread works through close contact disease transmission. Meaning if you’re not living or working closely with someone who has the disease, you are unlikely to get it. Meaning, you’re unlikely to get this disease at the local store or restaurant or on a plane or in an airport. You’re more likely to get it at home.
- Our US PCR testing is seriously screwed up. We’re simply running too many cycles to amplify the viral RNA, making our tests have a ridiculously high false-positive rate. This means that based on the published data we have, that most people who have had a positive PCR test don’t have enough virus in their nose to actually infect anyone as the virus can’t survive to replicate itself.
- Asymptomatic people can’t transmit this disease, even to close contacts. Hence, quarantining healthy people because they have a positive test is no longer supported by the research we have right now.
The upshot? It’s great to see new larger studies being published that can answer these tough questions. Now we just need to make sure the folks making public health decisions have the courage to follow the evolving science rather than creating knee-jerk measures.
(1) Cao, S., Gan, Y., Wang, C. et al. Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China. Nat Commun 11, 5917 (2020). https://doi.org/10.1038/s41467-020-19802-w