The communications professional was diagnosed with relapsing-remitting MS in 2013.
Ms Callaghan said: “Cladribine is a disease modifying therapy which essentially wipes out and rebuilds the immune system, therefore I can’t have both at the same time.
“This is a frustrating situation as due to the fact I am in the shielding category because of the treatment, I have been told I would be eligible for the vaccine in February.
“I am grateful for the ongoing support of my MS nurse who is always there to provide information – however the decision to protect against Covid or protect against MS progression ultimately falls on the patient.