COVID Transmissions for 5-24-2021

A new coronavirus has appeared—but shows little pandemic potential

Greetings from an undisclosed location in my apartment. Welcome to COVID Transmissions.

It has been 554 days since the first documented human case of COVID-19. In 554, the Byzantine Empire reconquered Granada. The Empire recovered from a brutal plague pandemic to continue its quest to restore Rome. In the end it wasn’t to be, but the story of overcoming a pandemic resonates with me today.

As you may have noticed, I really decided to unplug during my vacation, and I really needed it. But now we’re back!

Today I want to talk about a new coronavirus, and then we’ll go through some reader questions that I think you’ll all be interested in.

Bolded terms are linked to the running newsletter glossary.

Keep COVID Transmissions growing by sharing it! Share the newsletter, not the virus. I love talking about science and explaining important concepts in human health, but I rely on all of you to grow the audience for this, which you can do by using this button here:

Now, let’s talk COVID.

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New zoonotic coronavirus detected in Malaysia

A story that caught my eye over the break is the discovery of a new coronavirus that has entered humans: https://www.npr.org/sections/goatsandsoda/2021/05/20/996515792/a-newly-identified-coronavirus-is-making-people-sick-and-it-s-coming-from-dogs

This isn’t something to fret over—we are not about to see a COVID-21 pandemic here—because the new virus does not seem to be capable of human-to-human transmission, at least not readily.

In this case, the animal vector that the virus spills over from into humans appears to be the domesticated dog. This is a classic story; the entry of a new virus into the human population from an animal that we closely associate with. Once of the human coronaviruses is believed to have originated in cows, for example.

I share this story to demonstrate that these events are relatively commonplace. Humans associate with animals on a regular basis, and we get exposed to the things that they are infected with. Sometimes, there is enough compatibility between those pathogens and human biology for an infection to occur—and in some of those cases, there can also be disease.

With the SARS-CoV species, we saw two major spillover events, with the first causing thousands of infections and very serious disease, and the second causing a global pandemic that has killed millions. While that outcome is very unusual, I think what is not widely appreciated is how many times we bought tickets in this particular lottery before we got to the COVID-19 pandemic. There is a selection bias in the zoonotic viruses that we know about, because generally, we only pick up on the ones that cause disease.

In fact, even this canine virus is only known to us because it caused limited disease in humans. I can’t put a number on how many abortive spillovers may happen somewhere in the world each week, but amount to nothing because there is no disease.

So, what this story reminds me of—and what I find most educational about it—is that SARS-CoV-2 and the pandemic it has caused is not a sudden catastrophe, but rather the eventual and possibly inevitable outcome of processes that go on in the world continually. Looked at this way, I think it is easier to understand how a virus of this kind can emerge. If a family of viruses has many opportunities to enter humans, eventually one branch in that family will be the right one that causes serious disease that is also readily transmissible between people.

In the world we’re in now I see a lot of people grasping for explanations for how such a virus might have emerged—and turning to exotic explanations with little if any supporting evidence in the process. To me, these explanations sound outlandish because I spent years studying emerging viruses and I know how often zoonotic events can happen. To others, not knowing that these spillover events can happen relatively frequently, the emergence of SARS-CoV-2 itself may seem so exotic and outlandish in itself that it demands such an explanation.

But really, it is more likely that it is just the outcome of a long game of Russian roulette that we’ve played as a species by continuing to encroach on bat habitats. If you give a virus species enough chances, eventually it’s going to find a way to cause trouble.

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What am I doing to cope with the pandemic? This:

Hiking in the woods

I’ll be sharing some vacation photos. This one is from a hike through a waterfall-filled ravine in Falls Village, CT. I took this hike with my wife, but by her request, I try to keep her face out of photos I share on public-facing social media, so unfortunately you get the worse half of the deal and can see only me:

Photo is me, in a sunny, forested environment, in front of a small brook.

As it turns out, I really needed a vacation. Getting out in the world and seeing things other than my neighborhood and apartment is a powerful thing.

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There were quite a few comments on the last issue before my break, but there are a couple that I want to highlight.

First, from a reader calling themselves “Just Another Bozo on the Bus”:

Hi John - THANK YOU so much for the great service you are doing. I notice that India now recommends hydroxychloroquine, which I thought was pretty much discredited. Any idea what is going on there? Is this just another example of India bungling the pandemic, or is there som e value there? 

https://www.mohfw.gov.in/pdf/RevisedguidelinesforHomeIsolationofmildasymptomaticCOVID19cases.pdf

This is an important point, because the Indian government is currently recommending a number of discredited treatments for COVID-19. HCQ isn’t the only one, but since I was asked specifically about it, here’s my reply:

Thank you for commenting!

I don't know what the Indian government is thinking with that recommendation. HCQ has been over-investigated for use in COVID-19, and has been shown to be essentially useless for treatment of the disease. In a prior issue--from the end of last summer, I believe--I covered the fact that it was time to leave HCQ behind. Scientists and physicians have largely done so, so I'm not sure why it has been proposed again by the Indian government.

Reader Sam left the following question, which is also an important one:

It does seem increasingly clear that vaccination largely prevents infection, not just symptomatic disease. But this seems to get conflated with the question of asymptomatic transmission. Obviously, no infection means no transmission. But how strong is the evidence that breakthrough infections, particularly asymptomatic breakthrough infections, are less transmissible?

If vaccination essentially eliminates, or at least greatly reduces, the risk of asymptomatic transmission, that's great. But does it?

And how do variants factor into all of this?

A great question, but here, the answer is a little less clear-cut. Here’s what I had to say:

Good question. I think it’s fairly obvious at this point that the vaccines limit transmission, but that’s at a population level. It is somewhat difficult to interrogate just how much of an effect vaccination may have on transmission from asymptomatic “breakthrough” cases. But I have to note here that I don’t really think of these as breakthrough cases. These aren’t really cases at all, in my opinion. They represent cases that have been prevented, because there was no disease. On the other hand, asking if they are transmission-competent is reasonable.

The overall feeling that I have from the literature is that there is a substantial reduction in both the frequency of asymptomatic infections in vaccinated people, as well as a substantial reduction in the frequency of asymptomatic infections that are competent for transmission of virus. Asymptomatic infections were already thought to be meaningfully less efficient at transmitting, even in the absence of vaccination. With vaccination, there is evidence that a meaningful reduction is achieved in transmission-competency of asymptomatic infections. The problem is that it is very early on in the study of this question, so I do not feel entirely confident putting numbers on it.

Much of what I’ve summarized here is found in this review paper, which I find to be a great resource on questions of whether the vaccines can impact transmission: https://academic.oup.com/ofid/advance-article/doi/10.1093/ofid/ofab259/6278371

On the whole, it’s clear to me that there is an effect of vaccination in both reducing the frequency of asymptomatic transmission as well as reducing the odds of transmission of asymptomatic infection. What I can’t tell you is the magnitude of those effects.

There were some other comments that I may need to address in days to come. Stay tuned!

You might have some questions or comments! Send them in. As several folks have figured out, you can also email me if you have a comment that you don’t want to share with the whole group.

Join the conversation, and what you say will impact what I talk about in the next issue.

Also, let me know any other thoughts you might have about the newsletter. I’d like to make sure you’re getting what you want out of this.

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Part of science is identifying and correcting errors. If you find a mistake, please tell me about it.

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