You can disable the comments section. Simply press your edit hub button and then when you scroll down to the comments section, you can delete he capsule. You won't be able to see any comments at all on the hub any more but no one will be able to post on it either.
Another option is to change your comments settings for that specific hub - click on my account, then click on the comments section on the left side of your page. You will see at the top in green writing Global comments settings. Here you can disable any further comments but I do think that that disables further comments from all of your hubs which is something you do not want to do.
Oh I found out how, while messing around - click your edit hub button and then click the capsule that says comments. You will see the option to disable any further comments there. Click that and you should be set.