Answer :
It seems that you have missed the given options for this question, but here is the answer based on my research. How it is likely if their mother is correct and what it means for Ana's chances of getting sick again is that Sam could not get sick with the same virus again since he has acquired immunity to it, so he must have a different virus which Ana could catch. Hope this answer helps.
Answer:
If Sam only had a mild infection of the virus he might not have acquired immunity to it and could catch it again, as could Ana if she had a mild infection.
Explanation: