The Virus X is a germ warfare virus created by Baron Zemo in his plans to win the World War II over the Allies. But his plan was foiled in 1943 by Captain America, Bucky and the Howling Commandos in Italy.
When Baron Zemo tried to fire the Virus X sample from a nearby tank at Captain America, it backfired as Cap threw his shield at the tank and it spilled on Zemo causing his mask to stuck on him and suffered the effects of the Virus X he created.
Over the years, the effects of the Virus X is still on him and Zemo went to Arnim Zola for treatment and cure. But sadly, there was no cure for that virus and Zola's formula is the only thing to keep it from slowly killing him.
When the news of Captain America's return was rung, Zola had theorized that the Super Soldier Serum might reverse the effects of the virus and cure Zemo of his condition but he requires the DNA sample from Captain America in order to make the cure for the Virus X.But since Zemo had failed to get the DNA sample from Captain America, it means no cure for him, only be treated with Zola's formula for all time until he dies.
- Baron Zemo (being kept alive by Arnim Zola's formula)
Virus X is based on Adhesive X.