Are Ferguson using a convolution approach with exponentials in the compartmental model based on this statement:
> "Individual infectiousness is assumed to be variable, described by a gamma distribution with mean 1 and shape parameter ⍺=0.25. "
A multiple convolution of damped exponentials results in a gamma with each exponential narrowing the gamma. https://en.wikipedia.org/wiki/Gamma_distribution
Maybe not enough info to figure out the model? Probably more in these papers
> Ferguson NM, Cummings DAT, Fraser C, Cajka JC, Cooley PC, Burke DS. Strategies for mitigating an influenza pandemic. Nature 2006;442(7101):448–52.
> HalloranME, Ferguson NM, Eubank S, et al. Modeling targeted layered containment of an influenza pandemic in the United States. Proc Natl Acad Sci U S A 2008;105(12):4639–44.
Added 3/20 :The lead author Neil Ferguson apparently was infected https://twitter.com/leahmcelrath/status/1240848615255560193