Just as Edward Jenner used the pustules from milkmaids to inoculate

Just as X, so too Y
Just as X, so Y

Both are correct.

Option A and C eliminated

in option B, "deriving the smallpox vaccine of a live virus" is incorrect
it should be "deriving the smallpox vaccine from a live virus"
Eliminate B

in option E, "obtained the live virus in the pustules" is incorrect
it should be "obtained the live virus from the pustules"
Eliminate E

Option D is the correct Answer

Just as Edward Jenner used the pustules from milkmaids to inoculate against smallpox, effectively removing the scepter of death that had hung over the population, the smallpox vaccine today is derived from a live virus, which immunologists have obtained from the pustules of infected organisms.

A) the smallpox vaccine today is derived from a live virus, which immunologists have obtained from the pustules of infected organisms

The correct idiom is "Just as X, so Y". Missing the word "so".

When using the above idiom both X and Y must be parallel and compared logically. X = Edward Jenner Y = the smallpox vaccine. These are not logical comparisons.

B) so too do today’s immunologists in deriving the smallpox vaccine of a live virus, which has been obtained from the pustules of infected organisms

Derive X from Y is the correct idiom. Not Derive X of Y.

C) the modern smallpox vaccine itself is derived from a live virus that immunologists have obtained, coming from the pustules of infected organisms

Same error as A.

D) so immunologists today use the pustules of infected organisms to obtain a live virus from which the modern smallpox vaccine is derived

Correct used the idiom Just as X, so Y.

E) so modern immunologists have obtained the live virus in the pustules of infected organisms, from which the smallpox vaccine is derived

Derive X from Y is the correct idiom. Not Derive X in Y.

There seems to be a small meaning error here. The live smallpox vaccine comes from the live virus but in this answer choice the small comes from the pustules of infected organisms.

A) the smallpox vaccine today is derived from a live virus, which immunologists have obtained from the pustules of infected organisms
B) so too do today’s immunologists in deriving the smallpox vaccine of a live virus, which has been obtained from the pustules of infected organisms
C) the modern smallpox vaccine itself is derived from a live virus that immunologists have obtained, coming from the pustules of infected organisms
D) so immunologists today use the pustules of infected organisms to obtain a live virus from which the modern smallpox vaccine is derived
E) so modern immunologists have obtained the live virus in the pustules of infected organisms, from which the smallpox vaccine is derived

AC out
BE out
D remains

between B and D, the latter is much better.
In B, meaning changes, "too" is still correct.
However, " in deriving " sounds weird;
"today’s " is a wrong possessive pronoun;
"so too do" suggests the same "milkmaids";
"vaccine of a live virus" sounds wrong;
", which has ..." indicates that the clause ins unimportant and redundant

D is clearly the winner.

Idiom used = "Just as,So"
Correct answer is D!

OE:
Knowing this not too uncommon idiom is helpful. “Just as” will be followed by an independent clause (putting together “just as” with the independent clause will make it a dependent clause). At the end of that clause, there will be a comma. Immediately following that comma should be a “so” (the “too” is optional).

What’s important is that the part after “just as” and the part after “so(too)” should be parallel.

We can eliminate answer choices (A) and (C) because they do not follow the idiom.

(A) See above. Otherwise, this answer is grammatically correct.

(B) This answer implies that today’s immunologists use the pustules from milkmaids. Remember, the parallelism of the two clauses in the “just as…so too”: Just as Jenner used pustules from milkmaids…so too do today’s immunologists. The parallelism, both grammatically and semantically, is between Edward Jenner using pustules from milkmaids and today’s immunologists using pustules from infected organisms.

(C) See above.

(D) The parallelism between Jenner and today’s immunologists is maintained. The arrangement of the sentence maintains the meaning of the original: “the live virus from which the modern smallpox vaccine is derived.”

(E) implies that the smallpox vaccine is derived from the pustules of infected organisms, because of the use of “which”. Technically, there are three noun subjects “organisms”, “pustules” and “live virus”. Based on the “touch rule”, which “which” adheres to, “which” should refer to the first subject in a prepositional phrase. But with one as long as this, it becomes a little confusing just what “which” refers to. The correct answer in the GMAT would find a clearly way of expressing the fact that it is the vaccine is obtained from the “live virus”. Finally, “obtained FROM”, not “obtained IN”, is the correct idiom.

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