Explanation:

- Option 1: "a recent survey" - This is a grammatically correct phrase. It simply refers to a survey conducted recently.

- Option 2: "under the age" - This phrase is correct. It is used to describe children who are below a certain age.

- Option 3: "according to" - This is a common phrase used to refer to a source of information, and it's correctly used here.

- Option 4: "has been immunise" - This segment contains the grammatical error. The verb should agree in number. It should be "have been immunized" to match the plural subject "60% of children."