  One-dimensional systems proximity-coupled to a superconductor can be driven
into a topological superconducting phase by an external magnetic field. Here,
we investigate the effect of vortices created by the magnetic field in a
type-II superconductor providing the proximity effect. We identify different
ways in which the topological protection of Majorana modes can be compromised
and discuss strategies to circumvent these detrimental effects. Our findings
are also relevant to topological phases of proximitized quantum Hall edge
states.
