Wendy Barclay

So each respiratory virus transmits between people with a different efficiency.

And there are many, many different factors that play into that.

So from one side, it's the virus.

So it's about how stable is the virus in the environment and in the air.

Physically speaking, does it fall apart when it's warmer?

Does it sit in droplets which are falling more rapidly onto the ground, etc.

?

Also, what receptor does the virus utilise to bind and enter cells when it's received by the recipient?

So are those receptors abundantly expressed on the upper respiratory tract of the recipient, in which case we would expect very efficient nose-to-nose transmission?

Or are they only present in the deep lung, in which case the virus really has to be an aerosol to get down into the small airways and reach the receptors?

So that plays into it as well.

How does the virus fare with human mucus, which is an innate barrier which overlies many of the ciliated epithelium, which are the target?

Can the virus find its way through the mucus or is it rather rapidly expelled from the body?

So all of those physical features of the virus when it first emerges from an animal and finds its way into humans are going to determine the early R0.

But the R0, the number of people that one infected person infects, is also determined by all kinds of other things which are not really to do with the virus.

So the host, all right, how susceptible is the host?

Has the host ever seen anything like this virus before, which will modify how much shedding there is by one host in terms of passing virus on to another?

How dense are the hosts?

that are susceptible here.

Are they all living in very dense conditions or are they spread out?