Immunity Gain Speed

Immunity Gain Speed is a stat: The speed at which this character gains immunity to diseases. If this is too slow, the character will die from the disease before developing immunity. Its default value is 100%. The value shown in-game is rounded to the nearest whole percent, while exact value is used in calculations.

While this stat can be seen in-game, the actual immunity gain speed, measured in percentage per day, is hidden but can be deduced from thorough observations. It is calculated as a product of:

Base immunity gain speed for the particular disease. For example, 23.88% per day for human Flu.
InfectionLuck, a pseudorandom factor ranging from 80% (Bad luck) to 120% (Good luck). It is set independently for each disease instance (when multiple pawns are affected by a disease outbreak, each of them gets their own disease instance). Wound infections in different organs of the same pawn are different instances, but only InfectionLuck of the oldest active infection comes into play (and only one infection immunity develops in organism, opposing all infection instances).

Technical details. InfectionLuck is not stored in save file. Instead, it is calculated as a pseudorandom value depending on the world's seed (seedString) and disease's hediff ID (loadID). For example, it is ≈81.7511% for seed "InfectionLuck" and ID of 1947.

Immunity Gain Speed stat.

Immunity gain speed is not affected by medical tend quality.

Stat factors

Immunity Gain Speed stat is determined by many factors multiplicatively.

Capacities

Blood Filtration: 50% importance. No allowed defect. No Max. So,

Blood filtration factor = Blood Filtration \div 2 + 50%

Notable facts:

Malaria progressively reduces Blood Filtration.
A missing Kidney reduces Blood Filtration by 50%. This alone results in a Blood filtration factor of 75%.
Cancer progressively reduces efficiency in the body part affected, potentially reducing Blood Filtration if it is in the Kidneys or Liver.
Luciferium adds 70% to Blood Filtration. This alone results in a Blood filtration factor of 135%.
Detoxifier kidneys each add 5% Blood Filtration each compared to a healthy kidney. This alone results in a blood filtration factor of 102.5% (105% with two).
- This is mutually exclusive with Immunoenhancers

Saturation

Hunger/Food:

100%: Fed or Hungry
90%: Urgently Hungry (corresponds to Ravenously Hungry)
70%: Starving (corresponds to Malnourished)

Rest

Rest need:

100%: Rested
96%: Tired (corresponds to Drowsy thought)
92%: Very tired (corresponds to Tired thought)
80%: Exhausted (corresponds to Exhausted thought)

In Bed:

95%: When resting/sleeping in an ancient bed .
100%: When not resting/sleeping or when resting/sleeping on the floor, ground or (animal / double / baby ) sleeping spot.
105%: When resting/sleeping in a (double) bedroll or animal sleeping box.
107%: When resting/sleeping in an animal bed, (double) bed, royal bed, (double) slab bed or deathrest casket .
111%: When resting/sleeping in a hospital bed.
113%: When resting/sleeping in a hospital bed with attached vitals monitor.

Note that quality of the bed only influences the rest effectiveness, not the immunity gain speed.

Resting:

100%: Not resting. Also, when downed, despite visually lying.
110%: Resting, sleeping or skygazing (cloudwatching, stargazing, etc).

Age

Generally, the multiplier for age follows a curve defined by 5 points.

Age	Multiplier
0.65 * Life Expectancy	100%
0.80 * Life Expectancy	95%
1.00 * Life Expectancy	90%
1.20 * Life Expectancy	80%
1.50 * Life Expectancy	50%

As life expectancy is 80 for Humans, the following are approximate values for them.

Age	Immunity Gain Speed
<54	100%
54	99%
56	98%
59	97%
61	96%
63	95%
66	94%
69	93%
72	92%
76	91%
79	90%
81	89%
83	88%
85	87%
86	86%
88	85%
89	84%
91	83%
93	82%
94	81%
96	80%
97	79%
98	78%
99	76%
100	75%

Past age 100, it continues to gradually decrease until it hits 50% at age 120 and stays at 50% thereafter.

Misc

Immunoenhancer: +8% per, +16% max
- This is mutually exclusive with Detoxifier kidneys
Super-immune trait: +30%
Moral guide's Preach Health ability : +25%
Strong immunity gene : ×110%
Super Immunity gene : ×150%
Perfect immunity gene : No effect, prevents most common disease but does not cure existing disease
Inbred gene : ×85%
Mild cell instability gene : ×96%, ×300% Cancer rate
Major cell instability gene : ×92%, ×500% Cancer rate