Aerosol Research: How Much Security Does 2G Offer?

In Germany and also with you in Switzerland, the corona numbers are exploding.

Mr. Riediker, you are an occupational hygienist and are involved in aerosol research, did you expect this development?

I am not surprised.

We still have a high number of unvaccinated people and not a very high infection rate.

At the same time, many decision-makers have not yet understood what aerosol transfer means.

Politicians and citizens often do not understand how to protect themselves from aerosols.

In addition, the delta virus can be transmitted more easily than the wild type and the alpha variant.

You examined how delta viruses spread indoors in a study that has not yet been published.

Please explain to us.

In many infected people, Delta significantly increases the virus concentration in the respiratory tract and thus the number of viruses released into the air.

The highest concentrations that we measured have not become higher, but there are more people today who have very high concentrations in them.

With the earlier variants, and especially with the wild type from Wuhan, there were still very many people who only emitted traces of the virus.

The virus had not yet adapted well to humans and struggled to reproduce.

In many people, the immune response reduced the virus before it reached concentrations relevant to aerosol contamination.

How has Delta changed the distribution?

There are fewer people who only exhale low virus concentrations, but significantly more people who emit very high concentrations.

With the wild type I distinguished three types, an infected person with a high and a very high viral load and a superemitter with the highest viral load.

One in ten infected people had a high virus concentration in the original virus, now it is one in three.

This is a person who can infect another relatively easily if they sit in the office all day without a mask.

There was one infected person with a very high virus concentration in the wild type for every hundred infected, with Delta it is one in ten.

For example, this could be a school child who does not wear a mask and infects some classmates.

What about vaccinated people?

The well-known mechanism is that in freshly recovered and vaccinated people, the body activates various cell types that actively produce antibodies in order to recognize and fight the virus or viral proteins.

Over time, these antibodies disappear.

The cells that produce antibodies remain alive as memory cells.

As soon as the number of antibodies falls below a certain threshold, you can get infected again.

If a virus comes along, the memory cells quickly become active and produce antibodies again.

Often so quickly that we do not notice the renewed infection.

What about superspreaders?

I'm more likely to speak of super emitters because a person who breathes out a virus in the living room alone is not yet a spreader. In the past, out of a thousand infected people, there was only one who breathed out such an enormous virus load. With Delta, one in thirtieth is now a superemitter, our model calculations have shown. We know from contact tracing studies that numerous super emitters have infected over a hundred people. But how many people an emitter infects depends on the circumstances, for example the size of the room, the air exchange and the activity of the people. Speaking is particularly important: someone who shouts or sings loudly emits around a hundred times as many aerosols as a quiet person. At a yodel event in a hall, there can also be infections in the audience.

We Germans yodel less, but many sing in a choir.

Would you still join the choir in winter?