夏休みの間は

during summer vacation

→ 夏休み
phrase Rare #41,378
during summer vacation Means throughout or during the period of summer vacation. The は marks summer vacation as the topic or time being contrasted.
JA: 夏休みの間は、毎朝ジョギングをしていました。
EN: During summer vacation, I went jogging every morning.

夏休みの間はずっと家を留守にしていました

I was away from home for the entire summer vacation.

夏休みの間はずっとそこでキャンプしたんだよ

We camped there for the entire summer vacation.

夏休みの間はほぼ毎日泳ぎに行っていました

I went swimming almost every day during summer vacation.

夏休みの間は村に帰ったんだ

I went back to my village during summer vacation.