How should I poll a db table for a 'live' view in an MVVM scenario?

I have a log db table that I'd like to display in a GridView. I already have a view model that polls the db and updates the whole ObservableCollection if the table has changed. I do nothing else with this data, so I thought a further back model would be unnecessary.

However, now I'm starting to think it's improper that the viewmodel does any work with anything but the view and the model, and that I should introduce a model to observe the database and provide the viewmodel with any changes. The updated ObservableCollection in the view model then communicates the new data to the DataGrid in the view.