// Create a zombie. Make sure the model is already precached
local hZombie = SpawnEntityFromTable("npc_nmrih_shamblerzombie",
{
    origin = Vector(0,0,0),
});

local hScope = hZombie.GetOrCreatePrivateScriptScope();
hScope.QuerySeeEntity <- function()
{
    // Zombie can't see players that are infected
    return !entity.IsInfected();
}