Table 1. Relevant quantities of influenza virus and parameters in multi-strain SIR model.

Symbol	Definition	Typical values for influenza	Range in simulations
$I_a$	Fraction of population infected with strain $a$
$S_a$	Population average susceptibility to strain $a$	∼0.5
$I_{tot}={\sum }_a{I}_i$	Total prevalence
$\overline{I}$	Average total prevalence	0.005
$d$	Cross-immunity range		[50, 200]
$\beta =\nu R_0$	Transmission rate	∼0.5/day	2
$\nu$	Recovery rate	∼0.2/day	1 (sets unit of time)
$\gamma$	Host birth/death rate	∼0.01/year	0
$K_{ab}=e^{-|b-a|/d}$	Cross-immunity of strains $a$, $b$
${\tau }_{\mathrm{sw}}$	Coalescent time scale/sweep time	∼2-6 years
$T_{MRCA}$	Time to most recent common ancestor	∼2-10 years
$\delta T$	Fluctuations of $T_{MRCA}$	∼2-6 years
$s$	Selection coefficient	∼0.03/week	[0.003, 0.05]
$m$	Beneficial mutation rate per genome	10-3/week	[10-7,10-3]
$N_h$	Host population	1010	[106, 1012]