Coronavirus: Prevent Seeding and Spreading
By: Tomas Pueyo
Tags: Health, Coronavirus, Politics, Covid 19, Economics

Countries are reopening. They want to imitate the success of countries like South Korea or Taiwan. We now know they can do that with great testing and contact tracing, isolations and quarantines, by mandating home-made masks, with hygiene, physical distancing and public education.

These measures are all extremely cheap compared to closing the economy, but are they enough? Do we also need to keep schools shut? Businesses? Music festivals? Tourism? Are there other measures that are expensive for the economy but necessary to keep the virus under control?

The bad news first:

We will likely need to heavily slow down national and international tourism for months

Big events like business fairs or music concerts will need to remain closed for now

The good news:

We should still be able to travel for one-way or very long trips

There are ways we can accelerate the reopening of tourism

We can probably reopen schools

A clear order is emerging for which businesses should reopen. The most important to keep open are likely banks, grocery, and general stores, and the least important are likely cafés, dessert parlors, and gyms

Ok, let’s do this.

Imagine that your country has applied the Hammer reasonably well and now it’s getting ready to Dance. Some areas are still in quarantine, but the rest of the economy is slowly opening. Authorities are careful: mask-wearing is strongly enforced, all contacts are traced, all sick people are isolated in hotel rooms, and quarantines are enforced by tracking mobile phone movements.

Your country now has two goals:

Protect safe areas from infections coming from outbreak areas. I’ll call that “prevent seeding” of new cases. Prevent these seeds from developing into outbreaks. We can call that “prevent spreading”.

Countries must prevent seeding and spreading.

To prevent seeding, you need travel restrictions.

To prevent spreading, you need social gathering restrictions.

Since most countries are opening their countries and starting to allow social gatherings, it’s more urgent to talk about spreading. We’ll cover that first, and then we’ll explore seeding through travel.

The Coronavirus’ Favorite Events

Super-Spreaders

As I’ve already covered, you’ve probably heard of the superspreader from South Korea:

A single person, Patient 31, caused over 5,000 cases. That was the vast majority of cases in South Korea at the time. As of the middle of May, this figure still represents over 40% of the cases in the country — not counting all the spreading that might have come from it since. If this person hadn’t caused this outbreak, maybe South Korea would never have had one, like Taiwan.

You might have heard that this was caused by Patient 31 going to a megachurch twice. What you might not know is what such a service might look like.

Service at a Shincheonji church. Source.

At this church, thousands of people sit close to each other for long periods of time, forbidden to wear eyeglasses or masks, singing and praying loudly. The church doesn’t allow them to miss the service, even if they’re sick. That’s why patient 31 went two Sundays in a row to a service while sick.

In Part 2 of this article series, I explained how the virus spreads, via droplets and droplet clouds, expelled by coughing but also singing, or even talking. We also discussed how the virus prefers confined spaces shared for long periods by people who interact closely with each other.

This megachurch environment met all the requirements that increase the rate of transmission — talking, singing, and being in confined spaces for long periods of time — especially since nobody was allowed to wear masks or glasses.

As we have also seen in Part 1, something similar happened in Singapore’s dormitories.

As a reminder, this is a picture from the main dormitory, taken after the lockdown in that country.

Same thing: These are places with lots of people in close quarters having heavy social interactions that likely include lots of talking.

Migrant workers in their room at the WestLite Toh Guan dormitory in Singapore. Photo: EPA. Source: South China Morning Post. As you can see, the spread might not have been their fault, but rather an unavoidable consequence of their living conditions.

The brutal spread of coronavirus at social gatherings includes many other such examples. One is a choir in Washington State, where people sing loudly, close together, for a long period of time. 45 out of 60 people fell sick.

Over 4,000 people were infected across Europe through what might be a bartender in Ischgl, where apres-ski events are common.

Trofana Alm, an après-ski at Ischgl

The German area around Gangelt suffered 1,500 infections after a carnival, where people commingled, talked, sang, and kissed each other on the cheek.

This is an image of the event:

Source. Photo: Heinz Eschweiler

The other biggest outbreak in Germany was also due to a festivity. The German district of Tirschenreuth, with 600 cases, has the most cases per capita in the country after festivities to celebrate beer.

The list keeps going:

At Bondi beach in Sydney, at least 30 people became infected after attending a crowded dance party the night before gatherings of 500 people or more were banned.

In France, a four-day celebration at the Porte Ouverte Christian church gathered 2,500 worshippers, infected many, and seeded outbreaks across the country, including 250 people working at the Strasbourg University hospital or 263 cases in Corsica.

A soccer game in February between Italy’s Atalanta team, from Bergamo, and Valencia, from Spain, seeded what later became Bergamo’s outbreak, one of the biggest in Italy.

Even in Seoul, South Korea’s capital, which has some of the best coronavirus management in the world, 2,100 bars and clubs closed in the middle of May after a single infected person visited five clubs over a long weekend, infecting at least 100 so far. Over 1,900 contacts are currently being traced.

This is not limited to massive celebrations.

Weddings, funerals and birthdays generated 10% of early spreading events in the US. For example, this man from Chicago infected 16 other people at a funeral and 3 of them subsequently died. This makes sense, since people at these types of events often spend hours together, touching one another, hugging, talking. In this 50-person party, over half got infected, and these individuals then spread the virus across the US and the world.

These super-spreader events also happen in the business world.

At least 115 meat processing plants have had outbreaks in the US, affecting at least 5k workers.

Packing plant workers ( USDA ). Source.

A Biogen conference in Boston in early March caused around 100 infections and spread the virus to six states. At a fish factory in Ghana, one worker infected over 500.

And it’s not limited to blue-collar work. An call center worker infected around 100 coworkers (~45%) in South Korea.

Say goodbye to the open office.

All around the world — we see the same pattern time after time. Close proximity, social interaction, singing, talking, dancing, hugging, kissing, all for long periods of time in a confined environment… A pattern consistent with the model that most infections happen through droplets or droplet clouds while coughing, talking or singing. We have not heard of outbreaks coming from movie theaters, for example, where people are mostly silent and stay in one seat the entire time.

A scientific paper (pre-print) led by Dr. Carl Juneau, PhD — I’m a co-author — reviewed hundreds of other papers. For the flu, the evidence was mixed, but it looks like the type and timing of events mattered. What we found was that the flu is more likely to spread in events that are long, crowded, and indoors. Another study suggested that, for flu, limiting mass gatherings was only helpful just before or at the beginning of an outbreak (but would have little effect 20 days after the infection peak). Here are some relevant quotes from more recent publications:

“The best-available evidence suggests multiple-day events with crowded communal accommodations are most associated with increased risk. Mass gatherings are not homogenous and risk should be assessed on a case-by-case basis.” Nunan and Brassey (March 2020), Oxford University, not peer-reviewed. Results demonstrated that event cancellations can reduce COVID−19 infectiousness by 35%. Sugishita et al. (March 2020), not peer-reviewed.

Ferguson et. al. from the Imperial College believe the impact of limiting public events is a reduction in the transmission rate of around 12.5%.

With all this evidence, it’s clearer and clearer that the coronavirus loves social gatherings and crowded spaces. For those of us who love feeling part of a large group and meeting new people, we might be forced to say bye to them for the next few months. This is especially true if we are meeting lots of new people.

The Social Network

Another paper looked at how infectious diseases actually spread in social groups. The bigger the group, the faster the infection spread to the entire group.

Let’s look at the green line that says n=20, which represents a group with 20 people. This line shows that, as the transmission rate of a virus increases, so does the share of individuals in the group that become infected. And it does so faster than the normal population (the bottom dotted line). However, a group of 100 people will get most of them infected, even with a low infection rate.

Let’s compare a music concert with 10,000 people with a classroom of 20. In the concert, there’s a higher probability that at least one person is infected than in the classroom. On top of that, each person will interact with many more people, whereas in a classroom it’s capped at 20. And on top of that, the people in the music concert don’t know each other. They come from very different social groups, so the virus will then spread across all these groups, and these people will take the virus back to their groups, infecting them. Conversely, in the classroom, since it’s always the same group meeting, if somebody gets infected the infection largely remains contained in that group.

Big events are not just worse than small events. They are much, much worse.

Over the next few months, better research might shed light on exactly how much different social gathering events are impacting the spread of the coronavirus. In the meantime, what we can guess is:

Social gatherings should be avoided if a lot of people are close to each other, sing, talk a lot, or commingle.

Indoor, confined areas are much worse than outdoors activities.

Time matters. A short time is probably ok. Hours probably not.

Mixing different social groups is especially bad.

Conversely, small outdoors events where people don’t talk or interact are probably safe, especially if combined with measures such as masks, physical distancing and hygiene.

How can we use these insights to decide what types of events to allow?

Social Gathering Restrictions: Prevent Spreading

We can establish some rules of thumb. For example:

Cinemas or classical music concerts are probably much safer than rock concerts. In the first ones, a limited number of people are sitting close to each other but barely interact and don’t talk. They can also use masks if needed, and maybe seat 6 feet apart. In a massive rock concert, it’s hard to not sing, move about, or interact with lots of people around you.

Schools or small business meetings with the same people over and over are much safer than big fairs, travel for work, or big sports events. If somebody gets infected in the school network, many members might get infected too, but at least that doesn’t spread to many other places outside of that network.

If you have a wedding coming up, either cancel it, postpone it, or have a small ceremony in open air where people wear masks, don’t hug each other, and avoid talking as much as possible, especially from up close. Since doing all that would be very hard, it’s much safer to postpone it. In any case, if you do hold a wedding event, tell grandma or your diabetic cousin that you love them very much but that they really should not come physically. It’s a poor substitute, but under the circumstances a videoconference is their only safe option.

All of the above are early conclusions based on current — but scant — evidence. These conclusions will change. But with them, you can picture how risky an event is. What we’re trying to do is get to a place where we can estimate how many infections will happen at that event.