This is an excerpt from NHK Easy article: https://www3.nhk.or.jp/news/easy/k10012806691000/k10012806691000.html
My literal translation would be:
今年の６月までに６０００万人に使うことができるワクチンを買います [The government] will purchase the vaccine that can be used on 60 million people by the end of June this year.
The only way I can see this translated in more natural English would be:
[The government] will purchase enough vaccine for 60 million people by the end of June this year.
The grammar I am struggling with here is the relative clause 使うことができるワクチン - vaccine that can be used? Is my problem that I am trying to translate too literally, when I should just accept that this relative clause is approximately the same as saying "enough vaccine for..."?