How do outbreaks and chain reactions work in Pandemic?
When a city with 3 cubes of a color would get a 4th, it outbreaks instead: move the outbreak marker and put 1 cube of that color on every connected city. Any of those already at 3 outbreak too, but each city outbreaks only once per chain.
The rule:
In Pandemic, a city with 3 cubes of a color that would get a 4th outbreaks instead: move the outbreak marker and add 1 cube to every connected city. Any already at 3 outbreak in a chain reaction, but each city only once per chain.
A city never holds more than 3 cubes of one color. When it would get a 4th:
- Move the outbreaks marker forward 1 space.
- Put 1 cube of that color on every city connected to it.
- Any connected city that already had 3 cubes of that color outbreaks next, as a chain reaction: move the marker again and spread again.
During a chain, a city that has already outbreaked doesn’t get another cube from this card. A city can hold cubes of several colors, up to 3 of each.
During an Epidemic, a city that already has any cubes of that color is filled to 3, and then it outbreaks.
Role exceptions: no cubes or outbreaks happen in the Quarantine Specialist’s city or the cities connected to it, or in the Medic’s city for a cured disease.
If the outbreaks marker reaches the last space of the track, everyone loses.
Example:
A city with 3 black cubes is infected again. Instead of a 4th cube, it outbreaks, and every connected city gets 1 black cube. One neighbor already had 3 black cubes, so it outbreaks too. It can't send a cube back to the first city.
Why players argue about it:
Chain reactions are where groups go wrong: placing a 4th cube, or letting cities bounce outbreaks back and forth. Each city outbreaks at most once per Infection card.