Thread by @1goodtern

Very interesting new paper.
I hope this thread does it justice. 😬

"An integrated airborne transmission risk assessment model for respiratory viruses: short- and long-range contributions"

A new study from Royal Society Interface...

It's an update on the advanced airborne transmission model that shifts a little how we assess infection risks in indoor spaces.

TLDR: Short range spread is ten times as intense as long range spread.

This study builds on the CERN Airborne Model for Indoor Risk Assessment (CAiMIRA) but now integrates both short and long range airborne transmission into a single risk model.

Why does this matter...

Because most previous models assumed virus particles mix evenly in the air, but close range interactions don’t follow that rule.

Short-range airborne transmission (direct inhalation) = up to ten times the viral dose compared to long-range exposure (virus lingering in room air).

Now, that may sound like all the risk is therefore in close range interactions... but how long do you spend face to face and how much apart from each other?

Ten times the risk is exactly what I'd expect.

But if you're up close for only a tenth of the time... then how do the risks measure up against each other.

“In patient wards, the short-range viral dose is 10-fold higher than the long-range component, highlighting the critical role of close proximity interactions.”

But, again, you're still breathing the background air the whole of the rest of the time.

And if you mask up when close... but not when you're apart, where are you going to be exposed to the risk?

But... still... the dispersion rules are at work.
The closer you are to an infected person, the more concentrated the virus.

Masks and ventilation help... but if you're standing right in front of someone unmasked, you're getting a much bigger hit of virus.

And FFP2 (not even FFP3) masks reduce the risk by about 13x.

“Implementation of FFP2 respirators resulted in a remarkable 13-fold reduction in viral dose, underscoring the effectiveness of personal protective equipment (PPE).”

And... again... background exposure stacks up and up and up over time:
"An 8-hour exposure in a poorly ventilated office can equate to the risk of a 15-minute face-to-face, mask-less interaction."

Is the main problem sneezing and coughing?

No.
As I've been saying for years, the problem is simply breathing and talking.
“Vocalization activities have a big impact on emission rates, with speaking emitting two orders of magnitude more IRPs compared with tidal breathing.”

Loud, enclosed spaces like bars, gyms, and classrooms are prime transmission zones.

One of the most counterintuitive findings: individual “superspreaders” aren’t the main risk factor. Instead, secondary transmission is driven more by overall epidemic trends than by high emitters.

Some updated terminology:
Short range airborne transmission = inhaling virus from an infected person’s exhaled jet within a couple of metres.

Long range airborne transmission = breathing in lingering particles in room air over time.

Short-range is like standing in a smoky breath cloud.

Long-range is like being in a room where the smoke has already spread.

Both matter.
Short-range is where you get hit hardest over a short time, and long-range risk mounts up over time.

So how do we protect ourselves?

The study reinforces the classic old Hierarchy of Controls for infection prevention:

1️⃣ Eliminate the source (stay home if sick)

2️⃣ Engineering controls (ventilation, HEPA filters)

3️⃣ Administrative controls (reduced occupancy, distancing)

4️⃣ PPE (FFP2 masks for high-risk settings)

**Masks alone aren’t the most effective first-line strategy—cutting transmission at the source is.**

A quick snippet from a classroom study:

A teacher infects students mainly through short-range transmission. But over an 8-hour day, long-range risk also builds up.

🟠 Short-range risk (close to teacher): 70–100% chance of infection.

🔵 Long-range risk (further away, whole day exposure): 35% chance.

👉 If students wear FFP2 masks, long-range infections drop 5x.

👉 If the teacher wears a mask, short-range risk drops 6x.

Source control (infected people masking) is more effective than just protecting yourself.

Right... that had to be a quick one, I've missed a couple of bits... I'm off to take a funeral.

You can read the study yourself here...
royalsocietypublishing.org/eprint/IW3HQCN…