Go to the reference in your EndNote Library. In your EndNote record, add a comma at the end of the Corporate author:
| World Health Organization, |
When the corporate author name contains one or more internal commas, replace the first of those commas with two commas, and omit the comma at the end:
| School of Communication Studies,, AUT University |
Note: the same rule applies to complex names as well: Tom Bombadill of the Old Forest, if you want to keep it like that, put a comma behind the name.