Coronavirus: what we have learned about its transmission in the last year (and how it can change the way we fight it)

What was found? Much. From the identification of factors that dramatically increase the risk of infection, to the role of asymptomatic carriers. The analysis highlights key insights from the coronavirus, as well as misunderstandings.

Before a new variant of coronavirus emerged in the UK a few weeks ago, we spoke with Dr Cevik about what we can learn from this recent research.

What are the key findings from the analysis of the COVID-19 investigations?

Basically, we noticed that most of the infections occurred indoors.

Until maybe May or April, we thought that every interaction, every scenario carried a similar risk. But it is becoming much clearer that not all activities or environments are the same when we focus on transmission.

It is also becoming very clear that the duration of contact is important. The more time you spend with an infected person, and the larger the group, the greater the risk.

If you are in a closed environment and you are doing various activities – singing, shouting or eating – you will produce many more microdroplets. And if there is not enough ventilation in the room, those microdroplets remain suspended longer.

Studies have shown that opening a window reduces the risk of infection. For example [un estudio que examinó] an outbreak on a bus. And the people who were sitting near a window did not get infected.

[El estudio, realizado por la organización estadounidense sin ánimo de lucro MITRE, examinó la dispersión de aerosoles en autobuses con ventanas y ventiladores en 84 ensayos de prueba. No hubo pasajeros sentados en el autobús durante el estudio, si no que se utilizaron 28 sensores].

A lot of attention has been paid to hand washing, which is also important. But we must emphasize the fact that if you are spending a lot of time in a closed space, without the door or window open, the risk is still higher, even if you wash your hands.

Opening the windows is equally useful because we need six “air changes” per hour. If you open a window two or two inches in a small room, that could circulate the air for five people.

Another key factor is socioeconomic circumstances. The size of the home is quite important. For example, a study in France showed that if you live in very small places with many people, your risk of infection is three times greater than that of someone else who has more space.

How can these findings change your contact tracing strategy?

What we have learned in recent months is that the coronavirus tends to spread in clusters or clusters of people. But I think that this knowledge has not been fully assimilated into our way of thinking. And it has not been assimilated into our preventive practices either because we continue to focus on the dynamics of flu-like transmission, where each person frequently infects another person.

What we are seeing with the coronavirus is that most will not transmit the infection, but a small group of people can generate large clusters of infected.

So, knowing where transmission occurs and understanding high-risk environments can help us create a much more subtle and targeted strategy. And it could help us guide our contact tracing efforts. Because most people will have been infected by someone who also infected other people, often at the same time. That means we have to do a backtracking, find those people to identify the scene of the transmission.

As an example, South Korea found a small cluster linked to a nightclub and then tested everyone who had been to that club. That is not necessarily the type of contact tracing that we are doing at the moment in the UK because basically what we are following is the individual’s contacts.

Creating a strategy that focuses on clusters – identifying the places linked to high risk – could help us regain (a little) normalcy.

Could we avoid stricter containment measures by identifying these high-risk environments?

Exactly. That is what Japan has been doing. They basically advised avoiding crowds and close contact in closed spaces, especially if they involve talking or singing. That basically tells people where most of the infections are happening.

Right now, most public messages don’t make much sense.

Not just in the UK. For example, other countries mandate that the mask be worn outdoors. This may be useful if you are in an outdoor environment with a lot of people. But if you’re walking down an empty street with no social contact, you don’t necessarily have to wear a mask.

I think those messages are very damaging because people don’t really understand where the real risk is.

Many people still fear going to the supermarket, while they do sit in a restaurant for hours. The risk of transmission is very different.

People don’t stay long in a supermarket and it is also a huge space where you get little close to other people. But in restaurants, you are talking and eating in groups.

When in a group, people tend to feel more comfortable and do not follow the same measures as they do with people they do not know. That is where we are seeing the infection occur.

How problematic is asymptomatic transmission?

I think that asymptomatic people – who basically have no symptoms at all – are not contributing [al contagio] as much as someone who already has symptoms or will develop them later.

Asymptomatic people seem to be responsible for about 20% of all infections, and they are probably one third as infectious compared to those who already have or will develop symptoms.

That tells us we need to focus much more on symptomatic people – how to identify them early, how to test them early, how to make sure they isolate themselves during the most infectious period rather than trying to identify everyone.

There has been a lot of confusion around who to test. I believe that the asymptomatic contacts of any infected person have to be tested. But potentially, it’s not strictly necessary to test everyone. Japan, for example, is not testing everyone at the moment, they are targeting the big clusters and the places where there were infections.

An epidemiologist from Japan says his strategy is like looking at a forest and trying to find the clumps, not the trees. But he thinks the western world is getting distracted by trees and is a bit lost.

This interview has been edited for clarity and length.

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