It’s been a couple months since I did a post explicitly about COVID-19, or SARS-COV2, or coronavirus, and since the pandemic is still happening and is on everyone’s mind, I’m going to do another one today. This time, I’m going to do a big picture look at where we stand on transmission risks, reinfections, immunity, and what I think we need to keep in mind as we go forward.
Where do we stand with coronavirus?
How is it transmitted—and how can we avoid it?
What’s the deal with herd immunity?
What are my thoughts on the biggest challenges yet to come?
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What’s the riskiest place to be?
Indoor areas with low air circulation. Things seem to be spiking in hot areas where everyone stays indoors blasting the air conditioning and breathing in recycled air because it’s so damn hot outside. In regions where people get out into hot weather, like Hawaii, the virus is virtually non-existent. There are certainly other factors at play—Hawaii is an island protected by thousands of miles of water, for one, and they have a strict quarantine protocol for visitors—but many transmissions have been linked to indoor areas with AC.
Furthermore, all indications are that it’s harder to get infected from a “glancing blow.” Viral load—the number of viral particles you actually take in — is a big factor. If the initial load is small enough, your immune system has a better chance of fighting it off. If the load is too big, your immune system can get overwhelmed. What’s “too big” a load is different for everyone, but all else being equal, a larger viral load is worse. That’s why health care workers who spend a lot of time around infected patients are at a greater risk. But if you’re passing someone on the street? It’s going to be a much lower risk.
Is coronavirus easy to transmit outdoors?
I asked about this on Twitter the other day , wondering if anyone had good evidence of outdoor transmission. There were many responses. Some of the more notable ones.
- A 4th of July beach party in Michigan. Hundreds of people standing close together in knee high water, lots of house boats, “several” cases of coronavirus . There was also a house party a couple hundred miles away the same weekend that produced 40 cases. The indoor house party was much more virulent than the outdoor beach party.
- A Memorial Day party at the Lake of the Ozarks in Missouri. Very crowded, looked iffy. One attendee ended up with coronavirus, but officials haven’t identified any other positive cases linked to the party . I wasn’t able to find any recent updates to the contrary. The outdoor lake party didn’t seem very dangerous in this instance.
- No cases detected after the July 4th speech at Mount  Rushmore. They could still pop up, given the potential lag time between exposure and symptoms, but it looks good so far.
- There were also transmission cases after an outdoor graduation event and indoor prom on the same weekend. 19 students tested positive . All students attended both events, so it’s hard to determine if the cases occurred at the graduation event (which probably had indoor parties afterward) or at the prom (or both).
An earlier Chinese study found that out of 7,300 instances of person-to-person transmission, only one occurred outdoors.1  It happened during an extended conversation.
Overall, the most recent study I could find on the subject came to a similar conclusion.2  Researchers searched through PubMed, media stories, and any other legitimate reports on transmission events and found that the vast majority of transmissions occurred indoors.
This is good news, if it holds. It means people can feel a little safer about going outside, getting sunshine, getting physical activity, and living their lives. Avoid crowds and wear a mask when you’re around people, but I’m cautiously optimistic that being outdoors is the safest place to be.
Does COVID-19 spread through breathing?
This has always been the great fear. Does the virus spread through aerosol from simple breathing, talking, or are sneezes, coughs, and yelling required? Are aerosolized viral particles enough? Or do we need larger droplets?
A new pre-print just came out that has people worried. They took breath samples from symptomatic COVID-19 patients, found live viral particles in the aerosolized droplets, and found they could replicate on isolated human cells.3 
However, before you freak out, the story is more complicated than that.
Not all the samples grew; some subjects’ breath samples “didn’t take.” Some samples actually saw their viral particles decline in number. The smallest particles were the most successful at replicating, but the smallest particles also contained the lowest viral load.
The rate of growth was fairly low compared to how actual infections play out. The most successful samples only grew by 400% after six days. And that’s in an isolated human cell. When an entire human gets infected with COVID-19, the virus grows by thousands of percentage points every 8 hours or so.
That said, the virus is aerosolized, some of that aerosol contains replicable viral particles, and if you breathe enough of them in—probably by staying indoors with an infected person or people for an extended period of time — it’s possible to be infected. It’s pretty clear that larger droplets remain the big risk, though.
Can you be reinfected with COVID-19?
A pretty convincing thread  of anecdotes out of Iran (one of the earliest and hardest-hit countries) claims that reinfections are occurring. This would suggest that immunity wanes, at least in some people.
Some experts have floated the idea that COVID-19 may be the type of virus that stays with you and cycles through active and dormant periods, like Epstein-Barr or herpes does. It hasn’t been around long enough to know yet whether or not that is the case.
Can we reach herd immunity for coronavirus without a vaccine?
At first, the antibody immunity data wasn’t very encouraging: antibody levels in the population weren’t anything close to crossing the herd immunity threshold, and the antibody response to COVID-19 seemed to diminish and wane after a few months.
But more recently, scientists are finding evidence of robust and widespread T-cell immunity. T-cells from other coronaviruses, like SARS, various animal coronaviruses, and perhaps even the common cold may work on COVID-19. This cross-immunity is long-lasting, too; even though SARS hit 17 years ago, many of the subjects in the study still had T-cell immunity against it.4  In another study, between 20-50% of unexposed people showed t-cell activity against COVID-19.5 
From what I’m reading and hearing from experts, this has the potential to be a hugely positive development. My hope is that the huge death numbers are behind us, or at least trending that way. I hope those T-cell cross-immunity numbers persist in subsequent reports. I hope we start looking at T-cell immunity and not just antibody immunity.
Where I Stand
We’ll beat this thing. Of that there’s no doubt. We’ve made it to the other side of epidemics with much more primitive knowledge, tools, and technology. But here’s what I really worry about, other than the deaths, potential long-term health ramifications, and anything “physical.”
I’m seeing a lot of fear. I’m seeing people lose their appreciation for the rest of humanity. I’m seeing people use dehumanizing language to describe people who have different views on the seriousness of the virus. Neighbor doesn’t wear a mask? Don’t assume they’re evil or callous. Neighbor wants people to shelter in place? Don’t assume they’re authoritarians-in-waiting.
I worry about people who are too scared, too paralyzed to do the kinds of activities that are actually quite low-risk and would probably increase health and resistance, like going outside for hikes (even, gasp, with friends and family), getting sun and fresh air and exercise, moving through space and time rather than sitting hunched over your smartphone, scrolling through your echo chamber of choice.
Relax. Stay cautious and vigilant, yes. Stay safe. Don’t put yourself or anyone else at risk. No flippancy. But don’t forget to have fun and loosen up where you can. Low- to no-risk activities are out there. Do those.
If you have kids, they’re stressing out too. Believe me, they’re like sponges. They reflect what you’re giving off. Do it for them, if nothing else.
Lose the vitriol and the fear, more than anything. That stuff doesn’t go away so easily. Those divisions we’re building up between neighbors and family members and citizens may persist long after the pandemic has ended. Don’t let that happen!
We can do this.
Anyway, that’s how I’m viewing this whole coronavirus thing right now. Cautious but optimistic. What about you? How are you handling everything? Where do you see things going in the next few weeks?