Wards (and Bans)

By default Correspondence 2 can set Wards that inhibit or enhance the actions of targets within the ward (difficulty modifiers, slowing the ability to cross a distance, etc) and Correspondence 4 can actually Bar (completely disallow) entry or exit. Because this does affect the relevant patterns it requires the Spheres at the appropriate level to cast the effect being added to the ward. SEP fields (Somebody Else's Problem) require Mind 2, for instance, and fire attacks require Forces 2 and an appropriate source of fire, or Forces 3, Prime 2.

Wards and their Triggers can be confusing because the concept of a 'Trigger' isn't really used elsewhere in Mage. Trigger spells need to be able to determine when the trigger conditions for the Ward/Ban happen. Your ward needs to understand what a Vampire is before it knows to Ward the space against them.

This always takes the relevant spheres at rank 2. Setting triggers does not involve transmuting, altering, or in any way affecting a pattern so the rank doesn't vary with the target. Instead it functions like sensory magic (although it requires Rank 2 of the Pattern Sphere). Setting triggers against iron is Matter 2, against cats is Life 2, and against Vampires is Life 2, Matter 2.

So your Ward that sets all Vampires who step within it on fire is Corr 2 (for the ward), Life 2, Matter 2 (to set it for Vampires), and Forces 2 or Forces 3/Prime 2.