How does vaccination create a firewall?

A grid of people. Some are vaccinated (blue). An infection starts in the center. Watch how vaccination coverage determines whether disease spreads or is contained.

Dark = susceptible. Blue = vaccinated. Red = infected. Green = recovered.

What you're seeing

A grid of people. Some are vaccinated (blue), most are susceptible (dark). An infection starts in the center and tries to spread to adjacent people. Vaccinated cells are permanent barriers it cannot pass through.

How to read the graph

Dark cells can be infected. Blue cells are vaccinated and permanently immune — the disease bounces off them. Red cells are currently infected (they glow). Green cells have recovered. Watch how blue cells create walls that block the spread, even protecting unvaccinated people behind them.

The key lesson

You don't need to vaccinate everyone — just enough to break the transmission chains. This is herd immunity. The blue cells create a 'firewall' that protects even those who aren't vaccinated, because the virus simply can't reach them. The threshold depends on how contagious the disease is — typically 60-90%.

Susceptible1224

Vaccinated0

Infected1

Recovered0

Total Affected0.1%

Vaccination Coverage0%

No one is vaccinated. Press play and watch the infection spread freely through the entire grid. Then try increasing the vaccination rate to see the firewall effect.