Swedish Institute for Infectious Disease Control, Karolinska Institutet, Stockholm University
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Transcript of Swedish Institute for Infectious Disease Control, Karolinska Institutet, Stockholm University
Swedish Institute for Infectious Disease Control,
Karolinska Institutet,
Stockholm University
Martin Camitz
A stochastic model of a moderately A stochastic model of a moderately contagious diseasecontagious disease11 in Sweden and in Sweden and the effect of restricting travel as a the effect of restricting travel as a
control strategycontrol strategy
1Read SARS
A stochastic model etc…A stochastic model etc…
• About the model– Hufnagel et al’s model1
• Results
1Hufnagel, L., D. Brockmann, and T. Geisel, Forecast and control of epidemics in a globalized world. Proceedings of the National Academy of Sciences of the United States of America, 2004. 101(42): p. 15124-15129.
I
Stochasticitics… what?Stochasticitics… what?• What happens?
• When does this happen?
+I
R
I
Very randomVery random
SLIR-modelSLIR-model
IS L R
3 events
•Number of infectious
•Infectiousness
•Incubation time •Recovery time
etc…
×289
SLIR-modelSLIR-model
IS L R
3 events
•Incubation time •Recovery time
in Solnain Solna
•Infectious in other municipalities
•Travel intensity
•Number of infectious
•Infectiousness
in Solna
IntensitiesIntensities
IS L R
•Incubation time •Recovery time
•Infectious in other municipalities
•Travel intensity
•Number of infectious
•Infectiousness
QL QI QR
in Solna
1. Pick an event
QL QR
QL QI QR
QL QI
2. Pick a time step t
3. Update intensities
QIStockholm
4. Repeat from 1.
Kalmar
Solna
Run it on a really big Run it on a really big PC…PC…
You might get something like thisYou might get something like this
Or thisOr this
Just for sports, let’s not stop this time.Just for sports, let’s not stop this time.
• 1000 runs
• 60 days
• Average it all out
Much later…Much later…
Two questionsTwo questions
1. What happens if we restrict travel?– Say longer journeys than 50 km or 20 km no
longer permitted.
2. What if traveling doesn’t spread SARS as much as we thought?
Restricting travelRestricting travel
Restricting travelRestricting travel
Fiddling with inter-municipal Fiddling with inter-municipal infectiousnessinfectiousness
• Things that probably affect – Total travel intensity– Medium of travel– Type of transmission
• Does it matter?
Fiddling Fiddling with with
ResultsResults
• It works!
• Travel restrictions slow the spread– Lower incidence after 60 days– Globally and locally
• Comparatative results independent of