Here's why:
* It contains two independent clauses:
* "Laura and I have read many books"
* "during your summer vacation"
* The clauses are joined by a comma and a conjunction:
* The comma separates the two clauses.
* The conjunction "during" is used to join the two clauses.
Note: The sentence contains a grammatical error: "your" should be "our" because the sentence is referring to Laura and the speaker's shared vacation.