Ebola & "The Hot Zone"

[Bill P. Robinson]

I just finished reading "The Hot Zone" and I wondered if someone could
answer a question for me.

At the end of the book it is revealed that four workers at the Reston
facility has contracted the ebola virus.  However, the virus had
mutated into a new form that was not fatal.  Would these four
individuals now have any immunity to usually fatal form of Ebola (Ebola
Zaire) because their immune systems had presumably adapted to the non
fatal form of the virus (Ebola Reston)?

Is this possible?  

Any thoughts would be appreciated.

Thanks,
Bill