Table 1 Parameters of the infectiousness model.
NameSymbolDescriptionCentral valueUncertaintySource
Parameters directly calculated from data
Doubling timeT2The time taken for the epidemic
to double in size during the
early uncontrolled phase
of expansion
5.0 days95% CI: 4.2–6.4(20)
Incubation period
(two parameters)
s(τ)Lognormal meanlog
Lognormal sdlog
1.644
0.363
95% CI: 1.495–1.798
95% CI: 0.201–0.521
(21)
Generation time
(two parameters)
w(τ)Weibull shape
Weibull scale
2.826
5.665
95% CI: 1.75–4.7
95% CI: 4.7–6.9
This paper
Parameters with Bayesian priors informed by anecdotal reports or indirect evidence
Proportion
asymptomatic
PaThe proportion of infected
individuals who
are asymptomatic
0.4Prior = beta
(α = 1.5, β = 1.75)
Mode = 0.4
Mean = 0.46
Media reports
(Diamond Princess)
Relative
infectiousness of
asymptomatics
xaThe ratio of infectiousness of
asymptomatic individuals
to infectiousness
of symptomatic individuals
0.1Prior = beta (α = 1.5, β = 5.5)
Mode = 0.1
Mean = 0.21
Observation of few missing
links in Singapore outbreak to
date [suggestion from (19)]
Fraction of all
transmission
that is
environmentally
mediated
RE/R0Self-explanatory0.1Prior = beta (α = 1.5, β = 5.5)
Mode = 0.1
Mean = 0.21
Anecdotal observation that
many infections can be traced
to close contacts once detailed
tracing is completed
Environmental
infectiousness
E(l)Rate at which a contaminated
environment infects new
people after a time lag l
3Box function (0, n) days, prior
for n = gamma (shape = 4,
rate = 1)
Mode = 3
Mean = 4
(39); variety of values for many
different surfaces