HPV simulated.

What this shows

Risks can be hard to make sense of when they’re just numbers. This simulation makes the risk of HPV cancer tangible by following 1,000 people across a lifetime, showing who acquires HPV, who develops an HPV-caused cancer, and who dies of it. It then re-rolls the dice as if each had been vaccinated. The HPV vaccine prevents most of these cancers.

How it works

This is a Monte Carlo simulation, run year by year: for each person, each year, we roll dice weighted by likelihood.

Acquiring HPV. About 80% of people acquire HPV at some point, nearly everyone who is sexually active, per the CDC. Most infections clear on their own and cause no harm.

Which infections become cancer. Only certain high-risk strains cause cancer, and only a small fraction of those progress to cancer. The model splits infections across strain groups and gives each a progression rate calibrated to match observed cancer rates. These strain and progression figures are best-effort estimates from a synthesis of survey and registry data.

The HPV vaccine (Gardasil 9) blocks the high-risk strains it covers and prevents most HPV cancers. But the vaccinated re-roll may not yield zero cases; the cancers that remain come from strains the vaccine doesn’t cover.

Caveats. The vaccine also prevents genital warts, a significant benefit not depicted here. Individual risk varies by sex, screening, immune status, and other factors. Herd immunity benefits are not modeled. Late-in-life outcomes are less certain because the vaccine is relatively new.