Plague Conductor

The cloaked figure wipes their blade, walking away from a horrid fiend who falls to the floor, blood bubbling from their throat as a result of a deadly poison. Meanwhile, a tall masked man, cloaked in heavy leather treats a poor beggars sickness, secretly taking a sample of his diseased flesh for later research. The Plague Conductors act as a medical group, masters of all diseases and poisons. They treat the poor and sick, then turn around and use their knowledge of disease to slay their foes with horrid poisons. As a result of their dangerous job, most Plague Conductors have hearty immune systems, resisting infection from even the most unknown illnesses.

Malicious Medicines

Training with diseases has given you an intense medical background. You gain proficiency with Alchemist's Supplies, and if you use said supplies to create either a poison or antidote/cure, you spend only half the gold requirement. 

Weaponized Plagues

Using their knowledge of plagues and poisons for combat, Plague Conductors know how to apply the deadliest poisons to the strongest immune systems. At 3rd level,  you treat immunity to poison damage as resistance.

Additionally, you may deal sneak attack damage to any creature afflicted with disease.

Preventative Medicine

At 9th level, your skill with cures advances to the point where you can mix medicines that act as vaccines, strengthening the user's immune system. Every long rest, you may create vaccines, medicines that allow the user to gain advantage when rolling to resist or end the following conditions. Blinded, Charmed, Paralyzed, Petrified, Poisoned, and Stunned. These wear off after a long rest, and the creator must expend 2 gold per vaccine created. (price maybe adjusted by your GM.)

Additionally, your time working with diseases and cures strengthens not only your body, but also your knowledge of the medical world. You gain expertise in the medicine skill, and gain immunity to disease.

Potent Poisons

At 13th level, your skill with diseases allow you to mix poisons that are far stronger than your typical sickness. Whenever rolling for poison damage, you may treat a 1 or 2 as a 3. 

Malady Mastery

At 17th level, you have become a master of both poison and cures, able to bring horrid diseases upon your enemies and cure your allies of even the most dangerous blights.

You gain immunity to poison damage, and unless a creature has resistance or immunity to poison damage, you may deal poison damage as if they have a vulnerability.