Fig. 5.

These panels show the evolution of various modelled parameters for epidemics involving waning immunity. Waning immunity is described by a parameter ω representing the rate of loss of immunity (see Methods for details). For all epidemics ρ = 20 %, and the model is initialized with type O index cases comprising 1/1,000,000 of the population. Since type O transmits freely to all recipients, R(t) = R_max at time t = 0.

A: R_max = 4, ρ = 20 %, ω = 1/90 days⁻¹, “Western” population blood type distribution, 38 % A / 14 % B / 4 % AB / 44 % O.

B: R_max = 2, ρ = 20 %, ω = 1/90 days⁻¹, “Western” population blood type distribution as above.

C: R_max = 40, ρ = 20 %, ω = 1/90 days⁻¹, “Western” population blood type distribution as above. D: R_max = 4, ρ = 20 %, ω = 1/90 days⁻¹, “Indian” population blood type distribution, 21.4 % A / 39.9 % B / 9.4 % AB / 29.3 % O (Chandra and Gupta, 2012).

E: R_max = 4, ρ = 20 %, ω = 1/90 days⁻¹, “Peruvian” population blood type distribution, 18.9 % A / 8.1 % B / 1.6 % AB / 71.4 % O (Anon., 2021b).

For all sub-panels, X axis denotes days. Y axes: (first column) proportion of the population infected; (second column) R(t) as a fraction of R_max; (third column) distribution of blood types among currently infected individuals; (fourth column) cumulative risk of infection for each blood type relative to type O. The relative risks to different blood types during the final steady state depend on R_max (compare A,B,C) and on the background blood type distribution (compare A,D,E). The final case burden depends on all of R_max, ω, ρ and the background blood type distribution.