Learn Farsi: کسی با این واکسن بیماری را درمان خواهد کرد. - Someone will cure the disease with this vaccine.

To make the future tense of a compound verb, you keep the non-verbal part (درمان) as is, then add the conjugated future helper verb (خواهد for "he/she/it/someone"), and finally the short infinitive of the action verb (کرد). This gives us درمان خواهد کرد.

Why do we need را after بیماری?

را is the definite direct object marker. It tells us that بیماری (disease) is the specific thing receiving the action of being cured. Because of را, we know to translate it as "the disease" rather than just "a disease".

What does the ی at the end of کسی do?

The word کس means "person". Adding the indefinite ending ی turns it into کسی, which translates to "a person" or "someone".

Why are all three parts of the verb (درمان خواهد کرد) placed at the very end of the sentence?

In Farsi, the verb generally goes at the end of the sentence. Even though this is a long, three-part compound verb in the future tense, the entire phrase درمان خواهد کرد acts as the main verb, so it must all sit together at the very end.