COVID Transmissions for 8-6-2020
Greetings from an undisclosed location in my hotel room.
It has been 263 days since the first documented human case of COVID-19.
Housekeeping note:
I found a lot of interesting headlines today that led to long explanations; I’d like to hear if anyone wants to see an in-depth story about any of these, or if anyone has follow-up questions.
Glossary terms are bolded words with links to the running newsletter glossary.
If you like what you see—or what you might see in the future—tell others about it so the newsletter continues to grow:
Now, let’s talk COVID.
8 days of shedding
I am frequently asked how long a person who has had COVID-19 should wait before they are able to safely exit isolation. The answer I give is almost always 14 days after the resolution of symptoms, and I do still think this is a good answer.
However, it appears that shedding of virus may taper off as early as 8 days after symptom onset, as described in a paper in Emerging Infectious Diseases: https://wwwnc.cdc.gov/eid/article/26/11/20-3219_article
I wouldn’t make too much of the 8-day number; this paper has a small sample size that is geographically restricted to Hong Kong, so I think we should take it with a grain of salt.
What’s really interesting here though is that the researchers went to great effort to tell the difference between infectious virus and genomic RNA. Many stories have shown patients testing positive for viral genomic RNA for months after their infections have resolved; this is common with RNA virus infections and does not mean that these people are still infectious. What’s happening is that these patients are still clearing our debris from the contained infection, and so fragments may still be detectable.
Instead, to find out if someone is contagious, what we look for is a sign that the virus is actively replicating. This can be accomplished either by recovering virus and culturing it in cells to detect its presence, or by looking for the presence of transient products that are only made while the virus is replicating. In this paper, the authors looked at “subgenomic RNA,” which is a product of the virus’s active replication process. It is thought only to be present during an ongoing infection, making it a useful surrogate for understanding if infectious virus can be recovered.
However, the authors also rightly looked for infectious virus, which they found. Both infectious virus and subgenomic RNA were not recoverable beyond 8 days after symptom onset.
This is an important paper because of that last finding—since the subgenomic RNA and the virus culture essentially agreed with each other, this may suggest that testing for subgenomic RNA may be a way to test if a patient is still shedding infectious virus. Perhaps this finding will help us develop tests that tell us when it is safe for a patient to be discharged from the hospital or to exit quarantine.
Did lockdowns hurt economic activity?
This is not going to be an easy question to answer because of the complexity of active economies, but we do need to do our best in understanding the economic effects of lockdowns. A new paper in the Proceedings of the National Academy of Sciences attempts to compare economic activity in Denmark, which did have a lockdown, with activity in Sweden, which did not:
https://www.pnas.org/content/early/2020/07/31/2010068117
The researchers determined that negative economic impacts were minimal as a result of lockdowns, and that such impacts tended to balance out for high-risk individuals due to the prevention of disease in the long run. Overall the work appears to show that a small amount of pain inflicted to get the disease under control can prevent a great deal of damage to vulnerable parts of society.
Preexisting T-cell immunity
There has been some conversation about preexisting immunity to SARS-CoV-2; evidence from archived samples suggested that there were cross-reactive T-cells in samples going back several years before the pandemic. As mentioned earlier this week, this may be a start toward explaining why there are differences in severity of COVID-19 between different individuals. However, I still couldn’t tell you if having these T-cells helps you or hurts you.
That said, a paper published this week in Science has started the process of trying to understand these preexisting responses: https://science.sciencemag.org/content/early/2020/08/04/science.abd3871.full
The researchers here were able to determine what everyone suspected: that these T-cells were created as part of responses to existing, circulating human-adapted coronaviruses. This is interesting because antibodies against human coronaviruses do not appear to cross-react with SARS-CoV-2, but apparently the story is different from T-cells. I will keep tracking this story as it develops.
It’s worth noting that these cells aren’t providing a complete immunity; see this tweet thread for further reading as to why:
Testing and reopening colleges
A paper in JAMA shows some modeling work about how to safely reopen colleges: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2768923
This paper looked at 5000 hypothetical students and asked how frequently testing would need to be performed in order to minimize spread through the population if these students returned to campus.
The ultimate finding of this modeling was that to keep a campus outbreak under control, testing would need to be performed every 2 days, at an estimated cost of $470 per student per semester.
What am I doing to cope with the pandemic? This:
Vacation
The view from the Wagner brewery today was beautiful:
Remember to take time for yourselves, everyone, as you find the opportunity. It’s hard to run a disaster marathon without taking any breaks.
Join the conversation, and what you say will impact what I talk about in the next issue.
Also, I welcome any feedback on structure and content. I want this to be as useful as possible, and I can only make that happen with constructive comments.
This newsletter will contain mistakes. When you find them, tell me about them so that I can fix them. I would rather this newsletter be correct than protect my ego.
Though I can’t correct the emailed version after it has been sent, I do update the online post of the newsletter every time a mistake is brought to my attention.
No corrections since last issue.
See you all next time.
Always,
JS