β_{i} 
is the basic transmission
rate for strain i.

σ_{i} 
is the rate at which individual
move from the exposed to infectious class.

γ_{i} 
is the
recovery rate for strain i.

δ_{i} 
is the rate at which individuals
leave the quarantine class.

ν

is
the per captia birth rate

μ

is the per capita death rate.

ρ_{i} 
is
the probability of infectioninduced mortality 
φ_{i} 
is the
coinfection probability 
ξ_{i} 
is
the temporary immunosuppression/crossimmunity 
α_{i} 
is the permanent
immunosuppression/crossimmunity 
ψ_{i} 
is
the differential infectioninduced mortality 
N 
is
the population size, set equal to 1.

S(0)

is the initial proportion
susceptible to both strains.

E_{i}(0)

is the initial proportion
exposed to strain i, but no
history of the other strain

I_{i}(0)

is the initial proportion
infectious with strain i, but
no history of the other strain 
C_{i}(0)

is
the initial proportion
convalescing with strain i,
but no history of the other strain 
R_{i}(0)

is the initial proportion who
have previous experienced infection with strain i

R12(0)

is the initial proportion who
have previously been infected with both strains.

ε_{i}(0)

is
the initial proportion who are exposed to strain i, irrespective of their history
with the other strain.

λ_{i}(0)

is the initial force of
infections due to strain i.
