Infectivity is a plague statistic that dictates how infectious the plague is.
The more infectious a plague is, the faster it spreads.
Infectivity can be increased from all of the trait types, not just symptoms, but abilities and transmissions as well. Almost all symptoms can increase Infectivity somewhat. The Infectivity bar can (but will not do so when evolving Transmission) bring up the Severity or Lethality bar along with it, as some symptoms do have severe/lethal traits. However, governments can still detect your disease even without any severity or lethality. The chance of this happening increases as the difficulty increases. If a player wants to avoid their disease being detected, Coughing and Sneezing are probably their best bet for symptoms, while almost all transmissions and abilities do not raise anything but infectivity.
Players should note that although abilities do not appear to increase infectivity in the infectivity bar, they nevertheless increase your disease infectivity.
Transmissions do not increase Severity or Lethality.
Some Symptoms can increase the plague's Infectivity but are also likely to increase Severity and, in the case of high-tier symptoms, increase Lethality as well.
Abilities do not typically increase Severity or Lethality, although the Bioweapon has an exception: the Unlock Annihilate gene ability, which radically increases the lethality of the plague.
- It is displayed as a pink line on the Disease Graph, as it is a bar of the same color in the symptoms menu.
- If you have exactly 1.5 infectivity points, you are undetectable. This is why you get noticed on parasite after you evolve symbiosis.