You're over-applying a rule. It is correct to use 'will' here, because the second half of the sentence is not actually a time clause. Try replacing the 'when' with other words, for example: No one can predict how the disease will strike again. No one can predict where the disease will strike again. As you can see, the second half of the sentence is not dependent on the word 'when'. This is a different construction from, for example, "We will be more prepared when the disease strikes again", which does contain a time clause.

"When..." doesn't give a time for the sentence, so it is not a time clause. The clause "when the disease will strike again" is the object of the verb, "to predict". The original sentence is perfectly correct.

It is correct, and you shouldn't change it.