The new strategy successfully prevents the virus from defeating the immune system.

defeating 是动词 defeat 的现在分词形式。defeat 由前缀 de-（表示"向下、去除"）和词根 feat（来自拉丁语 facere，意为"做、完成"）组成，本义是"使失败、击败"。在这里指病毒"战胜"或"破坏"免疫系统的过程。