Papers

Peter Cotton's papers and notes on epidemics. Shorter pieces are under Essays.

Preprints

• Cotton, P. (2020). Repeat Contacts and the Spread of Disease: An Agent Model with Compartmental Solution. Preprint. arXiv:2005.10311. SIR with transmission attenuated by the probability that a contact is new, derived from agents moving in the plane. How fast acquaintances go stale changes final sizes by an order of magnitude.
• Cotton, P. (2020). Addressing the Herd Immunity Paradox Using Symmetry, Convexity Adjustments and Bond Prices. Preprint. arXiv:2006.07341. The growth convexity from the moment generating function of the transmission rate, or Vasicek's bond formula for an Ornstein–Uhlenbeck rate, and the harmonic-mean convexity at the peak. Summarized on mixtures and convexity.

Working papers and notes

• Cotton, P. (2026). Where Epidemics Turn: The Immunity Factor from Contact Surveys, County Waves and Serology. Notes in preparation. Summary · code and log. The rule $1 - R^{-1/\lambda}$; closed forms for time-varying activity; $\lambda$ from contact surveys with nothing fitted; tests on US counties, Spain, Sweden, England, Geneva and Manaus.