Symptom Combos are special combinations of symptoms (and in some cases infections) that can affect plague stats, such as slowing Cure processing with the Walking Dead, or increasing infectivity with the Projectile Vomiting. All combos have an achievement associated with them.
To achieve a combo, one must evolve two or more different symptoms. They range from two tier 1 symptoms to eight symptoms and two infections, so using them is a legitimate strategy for new players and advanced players alike.
|Projectile Vomiting||Increases Infectivity|
|Walking Dead||Decreases Cure Production|
|Profuse Bleeding||Slightly increases lethality, greatly increases infectivity|
Lowers productivity but draws attention to the plague.
|Public Defecation||Increases infectivity and cure research speed|
|Swine Flu||Slight increase in work needed for a cure||
|--------||All combos above are standard, the ones below are exclusive to the Necroa Virus.||------------------|
|Increases Severity, Infectivity, and Lethality.|
|Tank||Slight Severity boost|
|Spitter||Slight Severity boost|
|Boomer||Slight Severity boost|
|Walking Contradiction||Slight Severity decline||Photophobia, Cathemeral Shift|
|Runner||Slight Severity boost|
|Bath Time||Infectivity Boost|
- The Boomer, Tank, and Spitter combos may be based on zombie types from Valve's Left 4 Dead franchise.