Contagiarse

[solfinker]

Convencido desde el principio de que se encontraba ante una importante obra, no se dejó contagiar por el escepticismo que algunos le demostraron

My attempt:

Certain as he was from the start of that he was before an important work, he did not allowed to get infected by the skepticism that some showed him

[gentle]

I would try some creative writing as follows,
"As convinced as he was, right from the start, that he was facing an/a (important task-masterpiece, etc.), he did not let himself be influenced by the skepticism that some showed him..." or "As convinced as he was, right from the start, that he was facing an/a (important task-masterpiece, etc.), he did not let himself be carried away by the skepticism that other/s (people, colleagues, etc.) showed him." I'm sorry, but infected sounds too literal to me!

[solfinker]

It IS too literal! Thanks a lot!