Ultimate Christmas is a symptom combo exclusive to the Santa's Little Helper scenario. When this combo is active, Santa and Rudolph will come out of retirement and pose with children for pictures, making them very happy. It increases infectivity and happiness.
| Symptom Combos | |
|---|---|
| Standard Plagues | Red Rain ▪ Oops ▪ Projectile Vomiting ▪ Public Defecation ▪ Red Rain ▪ Swine Flu Walking Dead |
| Simian Flu | Assassin ▪ Blind Genius ▪ Discovery Channel ▪ Fly Magnet ▪ Red Ape Redemption ▪ Rude Awakening ▪ Zombie Panic |
| Necroa Virus | Bath Time ▪ Blood in the Air ▪ Boomer ▪ Cranial Dispersion ▪ Runner ▪ Spitter ▪ Tank ▪ Walking Contradiction ▪ Vampire Bat |
| Shadow Plague | Carpe Jugulum |
| Cure Mode | Report thy neighbour ▪ Rules are for losers ▪ We're here to help ▪ Happy Frogs ▪ Weapon X ▪ In it together ▪ Humans weren't meant to fly ▪ Shut down everything |
| Santa's Little Helper | On The Naughty List ▪ Ultimate Christmas |