Biohazards are awarded when completing a game of Plague Inc. One can earn a maximum of 5 in regular gameplay and the speedrun feature, or 3 in Scenario gamplay.
Achieving 3 biohazards in a scenario will unlock its "Complete" achievement. (i.e. the player will earn the "Complete Ice Age" achievement for getting 3 biohazards in the Ice Age scenario).
Biohazard rating depends on your final score. Speed and cure progress both play a role in all modes and an easier difficulty level allows for more lenient requirements.
In a scenario, the baseline for 3 biohazards is a score of 65,000. This translates to BOTH a cure at 45% or less and days since first infection at 365 or less on Mega Brutal before any custom score multiplier. When run, scenarios that allow for more than one plague reflect the best biohazard rating for each plague and count towards a "full 100%" completion bar if every single plague available in each scenario was completed.
In normal gameplay, the baseline for 5 biohazards seems to be a score of 100,000. Unlike scenarios, the requirements are not averaged out between two factors so there are plenty of ways to get the highest amount of biohazards even if the plague was very slow to reach a wincon.
Theories on how to earn a higher number of biohazards in normal gameplay are:
- an easier difficulty level
- a lower cure percentage
- how quickly the plague has reached one of its win conditions (days since first infection)
- the number of DNA points in a player's bank at the end of a game
- plague seriousness (Infectivity, Severity and Lethality), usually reflected by the total amount of DNA points spent
There are four different grades of biohazards that can be earned in the scenarios: bronze, silver, gold, and black surrounded by gold.
Cheat Plagues will not record the final score nor any biohazard obtained. The final score and biohazard rating will still be computed accordingly.