Mole rat disease

Mole rat disease is a potentially permanent effect the player character obtains if bitten by an infected mole rat in Vault 81 during the quest Hole in the Wall. The effect is -10 Max HP. During the quest, the Sole Survivor will obtain the only dose of the cure available. If the player character has contracted the disease then there is a choice to either save the life of Austin Engill, a young boy who was bitten by an infected mole rat himself, or use the cure on him or herself. If the Sole Survivor cures Austin of Mole rat disease, they will gain the favor of the vault as well as a room to stay in.

For tips on how to prevent contracting the disease, see the Notes section of the quest page.

Bugs
Tell the doctor the Sole Survivor is keeping the cure for themselves. Then, while the dialogue option to say "You're Right" is available, simply use the cure before choosing it. The Sole Survivor will be cured and everyone will react as if chosen to cure Austin.

It is possible to contract the virus without being bitten by a molerat. Probable causes are being near a live molerat or being near one when it burrows out of the dirt.