Who should you be talking to?

3 lessons in interdisciplinary proble

Joanna Masel

Ecology & Evolutionary Biology, Univ

WeHealth PBC
3 lessons

1) Your area isn’t the only one with unsolved qu

2) Find an expert in the right subsubdiscipline:

– Good experts direct you to still more relev

– Bad experts propagate misconceptions ins

3) Math can be a common language
Contact tracing

41% of SARS‐CoV‐2 transmission is before

symptoms appear (Ferretti et al. medRxiv 2020.09.04.20188516)

– Isolating the symptomatic isn’t enough– Find and quarantine contacts before

they transmit to anyone else
For SARS‐CoV‐2, contact tracing 

infected symptoms

test 

infectious positive

0 3 5 7

infected infectious sym

3 6 8

• Infected individuals c

transmitted long bef

tracers find them

• Apps promise instan
Design spec for exposure n

Get the right people to quarantine in time, and 

back to living more normally
Design spec for exposure n

Get the right people to quarantine in time, and 

back to living more normally

– 6 feet 15 minutes from someone ‐2 to +9 d

symptom onset

– Infected

1) Your area isn’t the only one with unsolved qu
Proximity in public tr
What’s up with the 6 foot 

2) Find an expert in the right subsubdiscipline

– Good experts direct you to still more releva

– Bad experts propagate misconceptions inst

../public health/exposure science/aerosols/viral 

Not ../public health/epidemiology
Particles come in a range 

Journal of Applied Microbiology, Volume: 127, Issue: 6, Pages: 1596
Where did 15 minutes co

• Murky: some early case study of smallpox?

• Dose scales linearly over time, of course

• Another propagated misconception is the min

– Makes testable prediction that dose‐respo

– They don’t
Targeting notifications to t

1. infectiousness of primary case

– 10‐fold variation depending on timing relat

2. duration of exposure

– proportional (no magic about 15 minutes)

3. distance/BlueTooth signal

– limited information about infection, even f

3) Math can be a common language re importa

Wilson et al. (2021) “Quantifying SARS‐CoV‐2 infection risk within the Googl

to inform quarantine recommendations” accepted at Risk Analysis, medrxiv 
Distance is informative because of human 

• N

• Co

cl

in

Wilson et al. (2021) “Quantifying SARS‐CoV‐2 infection risk within the Googl

to inform quarantine recommendations” accepted at Risk Analysis, medrxiv 
BlueTooth weights don’t matter 

Sensit

• Beta test of daily life in

real workplace

• Ground truth from QR

code scans

Positive predictive value

Threshold does
3. Math can be a common 

• Not everyone in public health / biomedical sc

• Often argue for “conservative” intermediate a

= treating risk inconsistently

• Final risk threshold sets conservative vs perm
What risk should trigger q

• This is an economics question (with lots of m

• Hard to compare lives vs. livelihoods

• Exploit fact that R(t) tends to average to 1 in 

• R(t) reduction achieved either by

– selective quarantine/isolation– indiscriminate social distancing– same units: reduction in social contact per 

Petrie & Masel (2020) medRxiv 20
What risk should trigger q

• Optimal is to quarantine anyone who, on that 

Expected(transmissions) than those not in qu

– Will lead to larger number of mostly short

• More information on E(transmissions) means 

achieve same R(t)

– good assessment of infection risk

– negative test results

Petrie & Masel (2020) medRxiv 20
Design spec for exposure n

Get the right people to quarantine in time, and 

back to living more normally
Design spec for exposure n

Get the right people to quarantine in time, and 

back to living more normally
Targeting notifications to t

1. infectiousness of primary case

– 10‐fold variation depending on timing relat

– superspreader status (20% cases → 80% in

2. duration of exposure

– proportional (no magic about 15 minutes)

3. distance/BlueTooth signal

– limited information about infection, even f

3) Math can be a common language re importa

Wilson et al. (2021) “Quantifying SARS‐CoV‐2 infection risk within the Googl

to inform quarantine recommendations” accepted at Risk Analysis, medrxiv 
Broadcast‐only beacons (GAEN c

contact tracers can use to mark su
Targeting notifications to t

1. infectiousness of primary case

– 10‐fold variation depending on timing relat

– superspreader status (20% cases → 80% in

2. duration of exposure

– proportional (no magic about 15 minutes)

3. distance/BlueTooth signal

– limited information about infection, even f

– indoors vs outdoors (estimated 20‐fold risk 

3) Math can be a common language re importa

Wilson et al. (2021) “Quantifying SARS‐CoV‐2 infection risk within the Googl

to inform quarantine recommendations” accepted at Risk Analysis, medrxiv 
Tradeoffs

Epidemiological effectiveness vs.

– Enough metadata with TEK to

quantify infectiousness

– Ability to do backward contact

tracing from superspreader

events

Privacy/sec

– Actual t– Percep

uptake

What is the relevant discipline to consult?
Not everyone

agrees with choice
What helps fight Co

• Target notifications to the infectedDesign spec:Get the right people to quarantine in time,

and let everyone else go back to living

more normally
What helps fight Co

• Target notifications to the infected• Notify them fasterDesign spec:Get the right people to quarantine in time,and let everyone else go back to living

more normally
What helps fight Co

• Target notifications to the infected• Notify them faster• Solicit behavior change (quarantine/testing)

Design spec:Get the right people to quarantine in time,

and let everyone else go back to living morenormally
The final mile

• Messaging effectiveness

• ENX does not permit

embedding of date
3 lessons

1) Your area isn’t the only one with unsolved qu

2) Find an expert in the right subsubdiscipline:

– Good experts direct you to still more relev

– Bad experts propagate misconceptions ins

3) Math can be a common language
Let’s talk, to fight this p

Am I missing a

discipline I need

to know about?

Can you point me

to a good expert?
Thank

you!

Amanda Wilson

Too many others to list, at the University of Arizona, W

James Petrie