World AIDS Day – The Mathematics of Epidemics

The HIV/AIDS pandemic has killed over 40 million people. Mathematical models (SIR, SEIR) guide treatment and prevention. The basic reproduction number R₀ for HIV is around 2–5 in high‑risk groups. Pre‑exposure prophylaxis (PrEP) reduces transmission by 99% – a probability model. Antiretroviral therapy reduces viral load, modelled by pharmacodynamics (differential equations). The number 336 reminds us that mathematics can save lives – by predicting spread, optimising drug allocation, and measuring the impact of interventions.