So it’s definitively an issue of something being an integer when it should be a float. I bet the following will fix it: change
y0 = [S0, 0, I0, 0, 0, 0, 0]
to
y0 = zeros(eltype(I0), 7)
y0[1] = S0
y0[3] = I0
And maybe the time-interval to floats too, i.e. (1., 36.), though I didn’t think this was necessary? ![]()