Before revision:  Following a mean field approach that models individuals like particles in a well-mixed solution, I derive a modified SIR model in which the  contacts between susceptible and infected population are reduced based on the known infection levels  .
After revision:  Following a mean field approach that models individuals like molecules in a well-mixed solution, I derive a modified SIR model in which the contacts between susceptible and infected population are reduced based on the known infection levels .