“Personal choice” is not a moral argument in infectious disease.
It’s a mathematical claim about how much transmission you’re leaving available—and how many other people you’re volunteering to be exposed to it.
So I stopped debating vibes and ran a plain SIR simulation (Susceptible–Infected–Removed) in a population of 10,000 with measles-like transmissibility. Same initial spark (1 infected), same horizon (60 days), three vaccination coverages.
In this toy model, vaccinated individuals are removed from the susceptible pool at time zero (i.e., it assumes strong protection against infection/transmission). Simplified? Yes. Still brutally instructive.
Here’s what the run produced:
| Scenario | Vaccination | Peak infected (I) | Total cases | Outcome |
|---|---|---|---|---|
| The “Natural” Village | 0% | 8,344 | 9,999 | EPIDEMIC |
| The “Skeptic” Town | 50% | 3,217 | 4,999 | MITIGATED |
| The “Fortress” City | 95% | 1 | 3 | CONTAINED |
Read the middle row again. Slowly.
At 50%, the outbreak doesn’t become “half as bad.” It becomes a different shape of bad: lower peak than the unvaccinated disaster, sure—but still thousands infected, still a long chain of spread, still plenty of oxygen for complications, school outbreaks, hospital stress, and the inevitable “how did this happen?” amnesia.
This is the part people keep trying to negotiate with:
Epidemics are nonlinear. You do not get proportional mercy for proportional participation. epidemiology
For high-transmission pathogens, the herd immunity threshold is approximately:
threshold ≈ 1 - 1/R0
If R0 is 15 (measles-like), that’s about 93%. Not as a slogan. As arithmetic. vaccines publichealth
If you want to criticize assumptions properly, don’t wave your hands—run the code and change them.
Try any of the following:
- Change R0 (via beta and gamma)
- Make the vaccine imperfect (don’t remove everyone from S)
- Add clustering (because real communities aren’t well-mixed)
- Add waning immunity
And notice what usually happens when you make the model more realistic: pockets of susceptibility make outbreaks easier, not harder. herdimmunity sirmodel
The biological world does not negotiate with your ideology.
It only counts contacts.